---
title: WWDC2003 Session 711
framework: wwdc
role: article
path: wwdc/wwdc2003-711
---

# WWDC2003 Session 711

## Transcript

Kind: captions Language: en morning everyone welcome to the audio in QuickTime session I hope you enjoyed that slight demo that we had of some of the things that we're going to be showing you today as well so this session is covering changes to the quicktime audio foundation basically the big changes were using Core Audio natively we're removing the code that's depending on sound manager this is bringing a lot of new capabilities to quick times audio infrastructure and as well we're going to talk a little bit about audio codec news so we're going to be focusing today on playback export some changes to DV audio that we made and as well news from the audio codec team and the technology frameworks that were covering today are quicktime and core audio and without any further pause i'm going to introduce greg chapman who's going to be talking about audio playback so we've been having a lot of fun as you might imagine so the main thing we wanted to do with this revision of quicktime was to remove all those restrictions that the sound manner manager put on us we wanted to have more than two channels per track you've been listening to some five dot one the linkin park and the bugs bunny was all five dot one so you can hear center right and left right and left surround and into the subs we wanted to have high sample rates Sal manager limited us to basically a 16-bit number for the sample rate we're talking to core audio now so we're doing much better on this front we wanted more than 16 bits per integer sample we could support playback of 24 and 32 bit integer but we would always bring it back down to 16-bit to play it out so you'd lose all that nice depth I we also wanted to support floating-point samples we used to be able to do this again we convert to 16-bit you lose all that nice deb the other thing we wanted to do was to be able to do multi tracks around where you could have for example four five dot one you could have six mono tracks each one labeled as being left right center whatever and then have them mixed together sample accurate come out all the appropriate speakers so let me go to demo two and let's show you what we've got I'm gonna play this whole trailer template part of it in the quicktime state of the union we want to see the whole thing since five dot one [Music] here we go [Music] he doesn't think that we perceive you [Music] all of our line we involve tonight I believe we can mr. Anderson [Music] please agree employment services [Music] and for fall [Music] good on you [Music] so you might ask what do you have to do to be able to play such content in your app and the answer is absolutely nothing your app can play this as soon as we shift this version of quicktime let me show you iTunes itunes doesn't know about quicktime support for multi-channel iTunes will play itunes does not use quicktime to play mp3s or the new music store content but if you handed a movie that doesn't know how to play it'll it'll use quicktime to play it here's an example of this is a linkin park song i think it's the same one we played when you came in takes a little bit so I'm not gonna play that whole song again as fun as it was so that's an example of an app that you know we just installed a different QuickTime underneath it plays back this movie it gets surround sound no worries okay let's go back to slides so how did we do that there's a couple of things there's some file format things we have to do there's a new version of the sound description that's in the tracks in the soundtrack I've described sample rate as a 64-bit float for example there's a new optional sound description extension that tells you what the channel layout is for the track is this left and right is it you know five dot one is it just left this is we've rewritten the sound media handler so that it can understand these things and it talks to core audio instead of the sound manager as you might imagine and the new multitrack mixture that i mentioned that does sample accurate mix between sound tracks so that you can have your surround between tracks we talked a little bit about channel mapping and how that works historically movies can I have one or more soundtracks usually they're alternates but you could have more than one soundtrack playing at the same time each track could only have one or two channels and if you had to we would just assume that it was left followed by right and if you had a multitrack movie it would always mix two mono or stereo depending what your output device was so if you had three stereo tracks you'd end up with stereo out and make certain amount of sense but it's kind of limiting in this lovely new world tracks going to have any number of channels there are assigned two speakers using a sound description extension as I mentioned and each track can contribute to the movies channel layout for example five dot one could be one track with six channels in it could be six mono tracks labeled according to what speaker they should go to or it could be a 5-channel track and then a 1 channel LFE track or you know free stereo tracks or whatever just you have to mark them appropriately and then we'll play them back correctly the order of the track in the movie is not important as long as the channel assignments are labeled and your old movies that have unlabeled mono and stereo they behave as before as you would back and if you're playing to a stereo device if i took that matrix trailer and you played it back on your computer with no you know six channel device plugged in that would down mix the stereo and you would hear you know left all the left side and the left all the right side on the right use your Center in both sides so let me show you a little bit about that will go back to demo 2 i've got three movies here there these are actually quad let me show you what they look like so the one change we made to player was to this particular panel so that it could display what the layout was he doesn't need to know the layouts in order to play it but in order to display the name of the layout he has to be able to do that and we'll talk a little bit later about how you can do that too so this one here this has got one soundtrack and that soundtrack has four channels and they're labeled left right left surround right surround lobster on the Rights around all the back speakers that's cool let's play that now this is very boring content but you'll be able to hear let it right that's array right Sarang okay thank you Kevin here's this one this is one has four tracks let's take a look at each one of those this first track is a mono track it goes in right second ones left surround the strange order but rights around and then left that's kind of cool is that going to go in the right places the right then sir ring right sir ring there's always that little hesitation before that one comes in that makes me nervous and this one's just to be different it's also for tracks this one goes left right left around rights around as you might expect and this want to play by correctly too but right then there we go right Saran okay so you can see that we're actually following the labeling we're not just doing something in the order of the tracks go back to slides okay let me talk about a few interesting new API is in QuickTime now that we're talking to core audio there's some new things you may need to do the first one is QT converts sound description we now have three different versions of sound descriptions if you look at sound descriptions yourself this is starting to become a nightmare so we put in an API where you can take any version sound description convert it to any other version sound description we have a mode where you can convert it to the lowest possible version of sound description given the format let's describe so that you can get the best possible backward compatibility when you're creating movies so old versions of QuickTime can play them and you can go to and from an audio stream basic description which is core audios struck that describes a stream of audio so that's very useful for just taking a sound description you convert it to an ASB D and carry on with core audio these are the the obvious ones you might want to have to set a movie to play to a particular audio output device device you IDs are a core audio concept it's a CF string so unique identifier for the device we used to have mediaset sound output component where you could grab a sound manager sound output component and say please play to this device if you call the old API we will try underneath to determine what the actual core audio device is that that sound output component was going to talk to and then we'll play to that guy will try and do the right thing we have two levels of API here one is to set the movie to play and then Mediaset is for individual tracks so you can as before set individual tracks and movie to play two different devices extract movie audio this is something that people have asked for for a while have a way to take a movie and just get uncompressed audio out of it mix across track decompress the tracks that are necessary this is the one that's going to allow you to do this and it returns a core audio buffer list which means you can then take that put it in a queue for some au graph to you know have a ball with and play it out or whatever you want to do these api's begin and I'm not really going to go through these I'm just going to show you some sample code that will be posted you can take a look at let's go to demo too okay yes it's unix i wrote a hook excuse me i wrote a command line app and i'm going to show you the routine that I wrote it just takes a movie extracts the audio uncompressed and writes it to a pay iff file which is a boring thing to do but I could imagine that you guys might think of something more interesting to do with the audio buffer list you get out of the movie so it takes a movie and it takes the name of the FF file you want we come down you begin movie audio extraction you can ask the audio extraction session what if the default output format is going to be and that default is generally 32-bit float it's all the channels in the movie from all the soundtracks in the movie it does no mix down by default and I think it picks the highest sample rate in the movie if there are multiple sample rates otherwise it's B sample rate so but I that's not what I want I want to put it in an aiff file so I want 16-bit big-endian samples so that's what I say here I do that by hand core audio has much nicer c++ classes for dealing with audio stream basic descriptions you tell the extraction session what you want so I send in what I want I wanted 16 bits per channel when I wanted signed big Indian blah blah blah allocate your core audio buffer list minds real simple I've only got one buffer because it's all interleave but you could get the interleaved float32 buffers if you wanted set up my aiff file and I call extract movie audio this is the interesting loop you watch this flags word that comes out of extract movie audio for this bit to be set when that bit is set you're done and each buffer you pull you write it out to the file or pass it off to your au graph whatever you want to do and then we do that so let me just show you this running I wrote a little bad script to do it because the command line tool is really ugly but let's see I'm in the same folder here and you'll watch that show up do it and over here we have suddenly an aiff file this is an AAC movie which is actually people who have tried to get audio out of movies by themselves it's really hard when you're dealing with a BB r codec there are seeming issues between buffers and you get pops and it's just a pain in the bud but here we are we've got this and it plays beautifully and loudly now that interestingly enough with stereo and it is a stereo and you just heard what we do with stereo when we have a multi-channel output which is we put it in writing the left as you would expect alright that was fun go back to slides now I'm going to bring up Brad Ford and he's going to talk to you about exporting these new kinds of audio [Applause] thanks Greg and thank all of you for caring enough to get out of bed early Greg said that we've been having a lot of fun I would use a different word to describe it probably pain but that's the whole mantra of QuickTime we write the hard code so that you don't have to and a great deal of pain has gone into making these bits playback to the right place at the right time and I we would really hate it if all this work were wasted by not giving you a way to author this content so thus we needed to give you a way to export to these formats as well so the QuickTime that ships with panther is quicktime 6.4 so let me give you an overview of the world before quicktime 6.4 our exports were limited in the same manner as our playback we could only do what the sound manager could do we also had problems with standard sound compression you may have seen this you may have called it if you are a programmer or if you're a Content developer you may have seen it when you export to AIF or wave it's the dialogue that comes up and gives you a list of all the compressors and the sample rates and options that you can compress to that's the standard sound compression dialogue or component I've had some problems with it it requires displaying quick times own dialogue to work well and right it actually has some property calls so you can use it with your own UI and just sort of try to use it as your state machine underneath but it was really envisioned to be driven by the dialogue so we did some things wrong we didn't always keep track of our state correctly we sometimes gave you the wrong codec settings and so this required you to have an intimate understanding of what the codec was doing underneath that was a pain for you the dialogue also offered some strange choices for compression formats sample size choices for compressed audio which is just wrong and also sometimes would show you various flavors of uncompressed masquerading as codex which is also very weird and wrong so now in QuickTime 6.4 we have a new standard sound compression component I'm kind of loathe to say it's a new dialogue because it's oh so much more it's a dialogue in one case but it's also just a sound configurator it can export to and from all the new formats we can play it back we'll let you export to it standard sound works well with or without quick times default dialogue which makes it easy for you to put custom UI on top of it so any application you might develop that would need to export audio you can use your own beautiful UI and just use our standard sound component to drive it and let it keep track of all the state ask it questions and we make this possible with new property api's which i'll be talking about in a minute also the default dialogue is now a lot smarter we don't make the same mistakes that we made before it's easier for me to show this to you then to talk about it so let's go to demo to okay we've got the same lovely riveting Warner Brothers sound effects content that you heard earlier I'm just going to bring up the export dialog I'm going to export to a QuickTime movie and this is the new standard sound dialog this is what the UI looks like you'll notice a lot of changes from the old one first of all gone are 32-bit float floating-point 24 bit integer and all the other uncompressed formats pretending that they were really compressed formats now if your uncompressed your uncompressed all the time and you get two different flavors of yourself by going down to this codec specific settings area where you can set your sample size to be what it really is and you can tell us whether you're floating point or unsigned or little endian things like that also of note are and I expect some oohs and ahhs here ooh that's a lot more channel layouts than we ever supported before you want to do mono or stereo that's fine you can still do that but you can also tag the content in your movie we'll let you export to as many tracks or as many channels as you have in your input movie so if you've got six tracks or six channels of audio in your input movie will prevent you know all the 50 s all the five dot ones makes sense also here's another la moment wow sample rates that go up beyond 64 so we'll let you go to 24-bit 96 kilohertz audio no problem and as a first let's go back to AAC where for the first time will let you export multi-channel AAC which opens up a lot of really interesting possibilities for web content delivery you know you can export AAC in the range of say 192 to 320 kilobits per second that's low enough that you could transfer it over the Internet sound pretty interesting okay so let's go ahead and save this out to the desktop okay here we go and let's quickly look at the info now we've taken all the tracks and we've put the audio in each track down into one track but it's still got all the channels they're just all in one track so we can play this back you get the idea AAC 5 dot 1 you witness it first in public ok let's go back to slide sleep that actually was the first public demo of five dot one AAC export in QuickTime feel special so what application changes are necessary many of you probably use these old friends these at ap eyes convert movie to file or convert movie to data ref if you do you'll know that the it has a lot of parameters and the last parameter is a component instance which is the component instance of the exporter that you're going to use and there are three ways that you can do this you can pass in nil for the last parameter which tells quick time I don't care what exporter you use just do the right thing you can also pass in a component not a component instance which means you find the right component of the type and subtype that you want but you don't open it and you say i know i really want to use this component but i don't care about special settings so still do the right thing it's the end the third one that you can do is you can actually open that component yourself do some special configuration to it and then pass it as that last parameter if you if you do the first case pass nil or the second case passing just the component you don't have to make any changes your export will work with the new settings you'll get the new audio exporting by default now if you do open your own movie export directly you must opt-in you must be explicit otherwise we don't know if you're prepared to handle the new properties and the new settings that we're going to give you so the way that you opt-in is you call this lovely new called QT set component property I'll be talking about these component properties in more in a minute but you can see you just tap in the exporter that you're talking about the class and the property ID is K movie exported property ID enable 2003 audio features pretty long property name and it's a boolean and if you say yes then you are telling us that you're ready to handle these new settings now if you have opted-in you may just need to opt in and you're done you will only need to make further changes if you call movie export get settings as Adam container and parse the settings yourself if you do that so I don't want to tell you not to do that but it's kind of risky to do that because we might do things like we just did when we changed audio underneath you and give you all different settings so if you part if you have code to parse them you need to be ready because you're going to get different settings also if you open the standard sound compression dialogues so just as a sidebar here the old one was of type s CDI standard compression dialogue and of sub type f oun sound so because it use the sound manager the new one is also SCD I but the subtype is and no offense to the German automotive industry audi aud I because it uses core audio so if you open up this new standard sound component by yourself because you want to configure settings or you want to use our dialogue you also have to change your code because we don't use the same calls as the old standard sound component so now let's address the bigger issue of the properties problem we in QuickTime are very lazy people much like yourself and if we solve a problem we don't want to solve it once we want to solve it for many other problems we want to get software reuse so there was a general problem here that we have a lot of components and they expose their properties in different ways so wouldn't be nice if we had a standard way for all components to expose their properties getting them setting them finding out if they have such a property listening to properties and we didn't have a way to do this and standard was sort of one of the first test beds for such a facility because it had roughly 50 new properties and we needed to decide how we were going to do this so that they wouldn't conflict with the old properties so what were our options I'll give you three options that we could have gone with we could have gone with the old if you've used standard compression before you know this call well sv get info and FC set info so this is a lovely call it lets you take your component instance of the step of the sound standard sound compression components and pass in a for care code that is the property ID you care about and then the don't void star so you have to know exactly what that type is if you don't bad things will happen you might crash or worse you might think you got the right information but you actually got some garbage so there has to be a special understanding contract between you and the component implementer so that was a little bit scary here's another option we could have gone with this is something that sequence grabber does create new get set pairs and shinbe existing selectors so you'll see in sequence grabber there are a lot of these pairs of get this guy set this guy this is nice because you can have custom parameters for each call but the downside is that you have a lot of interfaces to learn and you make typing mistakes and it does not address listenable properties these are just get as and setters and some existing API is required different data types the other option was to adopt a core audio model we liked what karate 0 is doing a lot because they give they have actually three standard calls the get info get and set and if you're talking about the how hardware abstraction layer they also have property listeners this was very close to the kind of thing that we wanted to do as well the only drawback I can think of is that each property class requires its own suite of calls so you have a set of gettin set and get info properties for audio units and audio streams and audio hardware we were hoping that we could make it general enough that all components could use the same calls so here is our solution a suite of standard come at property api's these are being inherited by core services so it's not just a quick time thing this is new and Panther and it's a system-wide thing so these are going to be in the negative range if you've ever written a component you know what I'm talking about there are some required selectors that you have to put in open closed version and there are some optional ones but also in the negative range these are optional negative range property selectors there's a component get property info component get property component set property and then two for adding property listeners and removing property listeners they can be implemented by any component including yours and we would encourage you to use them now there is one thing to know about these the new to Panther calls are prefixed by call component so it looks like call component getcomponent property info these are going to be shipped in Panther and forward if however you want to ship these properties in Jaguar then we have also released cutie prefix versions of these which have the glue is in quick time so we can ship it in Jaguar as well the property type is specified by a class as well as an ID that means you get to for care codes or eight care care codes to work with instead of just one for care code just kind of good because it sort of gives you a little bit of a buffer in the area of namespace collision so if I'm a component your component and I have sample rate property and you have sample rate property but yours is a float64 and mines and unsigned fixed I can still protect myself if our property names are the same because i have a class or care code that puts mine in a different space than yours also all of the data is explicitly typed in the get info call so if you make a get info call and you don't have to know anything about me you can just query me what are your properties I have to tell you what the type of the property is and the size so it's very explicit even if you don't have the header file what the property is ok so the get info call also gives you some flags that tell you some important things this is a logical extension of what they were doing poor audio as well they have a great call and get info that lets you see if the property is settable so ours gives you a bitmap of flag field that lets you see if perhaps yes the property is settable but I can't set it now maybe my hardware is not ready so maybe it'll return can set later or can get later so you can get meta information about the property by getting these flags out including one of the most important ones will notify listeners and I should mention standard sound compression the new dialogue has like I said about 50 new properties and I think all of them but five are listenable so you can build a very sophisticated app that's very dumb underneath because it's all it has to do is listen for property changes what do they look like so here are the actual calls I've already talked about them so I won't stay on this long it has a class it has an ID has the type which is also a for care code it has a size and then it has that flag field that tells you can get now can get later here is how you would implement a property listener let's say you are listening for my available sample rate list my available samples sample rate may change based on whether or not the compressor changes so you would set up my listener proc and you typically have a big switch statement in it in which you would handle all of the property IDs that you'd registered for so I just did a simple little printf statement there and go and update my UI and then you would tell the component like standard compression you would first make a new component property listing or upp and then you would register for that notification by saying call component add component property listener or if you're using the QuickTime version for Jaguar you would say cutie add component property listener with the exact same parameters and once you do that you are listening for that property and you will continue listening for that property until you remove it there is one important thing I should mention about these property ap is due to a minor oversight the glue code got into Panther got into the feed CDs that you that you received on Monday but the header file didn't make it there in time wasn't promoted to public status so that was a little bit of a minor oversight but we are making it available to you via sample code so if you go to the ADC developer site and look under quicktime you will find it there it's called QT component properties dot H and there you can get all of the calls and start using them so let's bring up a demo and show you these audio properties and youth can we go to demo too okay here is a great little app that was written by Adrian bear Locker another member of the QuickTime engineering team and I'm very proud of this app because he wrote it very quickly and it's the most slick under thousand line code app that one could write because it keeps no state all of its state is managed by the standard sound compression dialogue so maybe you're like Adrian you think that the standard sound compression dialogue is swell but you really just you know can't get enough metal in your life you want more metal or maybe you wanted to have your own custom UI look like he did so you are able to use standard sound to do all of your configuration and put up your own UI on top of it so let's take the same content we heard before that has the left right left surround rights around and we'll use his you I now remember this is being driven entirely by the properties so every time I tweaked a setting here it's doing a set component property call or its listening for changes and updating the UI so let's go ahead and do this export I suppose I should select an output location and we'll export it was a pretty full featured app and it's under a thousand lines of code but right right so there we took a quad and we mixed it down to stereo and it still plays in the right places if you'd like to learn more about the component property api's or standard sound compression in general please come to our lab between 12 and two today where you'll hear more thanks and I'll bring back Tim so feature was really really good we worked really really hard we were a little bit confused we might have been drinking strange things so we want to show you a little bit but we are going through can we go back to demo two please lefts around gone again oh man wish I didn't have to work on audio [Music] that's not right that's better oh that's much better quick comes back to normal [Music] [Applause] thank you so that was that was a stupid movie that a lot of people on the quick 19 work really really hard to film and direct and dream up I guess that was probably the eyes are the easiest of the hardest so I'm going to talk a little bit about some DV audio changes back to you know real content so we made some changes in QuickTime 63 the issue of DV audio was it as two basic ways that you can store DV audio inside of a QuickTime movie the first way is you can store inside track as PCM audio and basically extracting it from the DV frames as you capture that's what final set pro does like what QuickTime sequence crabber does and there's been generally no problems with long-term ad sink in that case the other way you could do it is you could have the audio track index every frame of DV and reference to VV audio inside the DV frame and that's what I movies doing when it captures and that's what the QuickTime DV importer is doing and the issue there is that audio in that case is represented as a fixed number of samples for DV frame which is a problem because it isn't if you look at the duration of a frame in NTSC it's basically a variable number of audio samples per frame and when we represented as a fixed value which is basically the maximum number that could occur we're basically accumulating adrift in some cases so in playback is fine but in our export and our editing cases we were accumulating about a one frame of video error in the audio for about every two and a half minutes of export or or editing depending on the case we had a fairly large problem with some AV sink in some applications so the solution that we decided to do is represent DV frames having variable duration which is really the correct thing to do so we have a new type which is v dva and it's a variable duration DV and that's new and click x 63 it's also going to be in 64 and forever after that's the default when you're importing it a DV clip when you use a little bit QuickTime importer and in iMovie it's now going to be representing them as variables through so a couple of reminders when you're looking at tvs you're playing around and actually looking at TV audio in the tracks you're going to see the new type k variable duration TV audio format you may see the old type because files that were created the 463 will still have the old type and the important thing is if you're playing with sound descriptions and you're using the new type you must set the compression ID to variable compression and that's how we basically make this work and so we've actually achieves a really good audio video sink and I just wanted to point out a couple of things a lot of the support that you're seeing will be available when quicktime six warships on jaguar as well that's something that we're working on to make sure that the multi-channel support etc is going to be working on that platform we're using a mobile I Oh audience to drive the audio the six channel audio connected via firewire and of course we're using the core audio support and their drivers to make that happen and with that I'd like to introduce oh one more thing one more thing which is for those interested in AV startup sync issues we have a session this afternoon at two where we're going to be talking about some changes we're making for audio video startup saying we figured that's more advanced programming in audio so we put it in that session and now I'd like to introduce Eric Aldrich she's going to talk about audio codec development thank you Tim [Applause] this is wonderful quicktime 6.4 built on top of core audio but now we're going to take a little journey to core audio land and talk about audio codecs this is what is an audio codec essentially it's the business end of the QuickTime on the audio side it's going to actually handle your encoding your decoding of your audio format on audio codecs are going to replace your s cons and your ethics they're now called 8x an ax and right now in your feed CD we have AC mp3 and IMA and we've already shipped AAC before quick time since QuickTime six okay so how do you go about lighting and audio codec well we make a little bit easier for you there's a lot of code involved but we provide you an audio codec SDK it's available on the air on the connect on apple com site your core audio we provide you a framework basically just needed to implement a codec it's a fairly basic but you can do quite a bit with it we give you some sample codec which is IMA for one important point to note is you do not have to implement both an encoder and decoder you can implement one and not the other example this is that mp3 we've only implemented to decode we have not implemented the encode another thing that's important about audio codecs is we use a push and pull model you could push the data in and you pull the resulting transformation out and keep that in mind when I'm talking about this further here okay required files for writing an audio codec fairly straightforward big one is there is a sea-based codec which is pretty much the be a base class for everything you're going to use this in every codec you're right we put this basically all these files provide the framework for what you will need to implement handles all the dispatching all the nitty gritty dirty details of talking to the sound converter and like our excuse of the audio converter which was detailed in session 404 okay we have an optional file which is a AC simple codec and this implements a basic buffer for very basic sound codecs audio codecs we provide buffer the buffering implementation for you you don't have to do it but for things that are fairly elaborate you're going to want to use something else and then you're going to have to deal with codec specific files for instance you're going to want if you're doing AC or mp3 you're going to want an AAC codec file you can inherit directly from either base or simple codec then you have just set you have several methods you'll have to implement and these are analogous to a few things that were already in the sound codex of course you have your get your property management which is get property info get property setproperty you have your initialize an uninitialized which is basically locked down the codec and then unlock it you have a pen input data which is the push of the push/pull model where you push your data in then you'll produce output packets which is your pull on the push-pull model and that's where you're going to get your decoded or encoded data out of ok a few things you need to think about like before you had open a component now that is handled mostly in the constructor your input your default formats we handle the end instructor as well ok you need to handle the encoder and decoder separately a model that we have used as we create if you have a lot of common functionality and codecs with your encoding or decoding so a lot of that we put into a generic you know here we see my codec and then we inherit directly from that we create my decoder my encoder and that's the model you want to think about it allows us to add for instance on mp3 we have you know an mp3 codec then inherent the mp3 decoder inherence mp3 codec and if we later choose to implement a 10 color for instance will also inherit directly from the mp3 codec file okay when dealing with properties I can't stress enough that this is probably the most one of the most important features of what you'll be dealing with this is basically you're configuring your codex before you lock it all down so if you're get property info it tells you how much data is required for each property and more importantly it tells you whether or not you can set it there will be two cases of this a you cannot set it or B you can set it when it the codec is not initialized and get into that little bit get property not all that much to say you just have to realize that that at any time this could be called and it is alright to answer I don't know if someone asks you for your bit rate your bit rate hasn't been configured you could say you know zero say I don't know or you can say just report the default but it's important understand that this can be called at any time there are some properties that won't even be known until after run times so it's possible you can just say I don't know setproperty again is not always available depends if the Codex been initialized or not initialize an uninitialized again initialize is just basically walking down the codec at that point when someone calls initialize whatever they have set you take that and that's how you set up the audio codec if they have not set all the appropriate properties it is if you can use default values and if you can make something out of it you can initialize at whatever settings have been set or you can or you can fail that's perfectly legal they haven't provided you enough data you can fail and enough uninitialized just simply removes this lock basically a boolean that I'm i initialize or am I okay a pen input data fairly straightforward you basically take your input data and you put it in internal buffer important thing to note though is you have to deal with audio packet you know audio stream packet descriptions all vbr codecs should handle these very important for mp3 AAC and the like CBR codecs you don't have to it's nice you can you can handle them if you choose but it's not really required produce output packets does the actual encoding or decoding whatever you don't have to have the actual encode decode right there using your call separate function or a separate library whatever to do it that's where you actually handle it and again I'm an encode side if you're a vbr codec you have to fill out the audio stream packet descriptions another thing to note here this is where you're going to actually handle clearing your input buffer even though their pen input data you deal with you know handling handing the data in and produce output packets you're going to update all your buffers you have to remember to do that here and backward compatibility kind of an important thing there's a lot of very well there's a lot of quick times fix their copies a QuickTime sticks out there and Panther hasn't shipped yet we allow you so you can deal the old escala mess deck world we give you sound manager audio components which allows you to wrap an audio codec so two old versions of QuickTime it looks just like an old Sound Manager component as deckhand s calm and we're going to be providing an SDK that does this on our monocyte anyway you will need to implement this if you want that support it's kind of important but very straightforward and we've been shipping these for a while this is how we implemented AAC from the get-go so this is proven technology and it's been working for quite a while so this point one important thing some documentation on all this read this here core audio overview which you can get basically connect on apple com take a look at it provide any feedback we'd appreciate it thank you [Applause] the non-technical is still here for the roadmap these are the sessions on technical quicktime we have a bunch of sessions going on also for content developers on a quick time one thing that is not noted here is that if you really care deeply about audio there is a feedback form starting just after we finish this session across the aisle here so if you have any comments that you want to provide to the audio team this is the right place to go and provide that we have a quick country that formed tomorrow afternoon we will welcome you all there if you have any questions so if you have any comments that you want to make about quicktime does my name and my address that you can use if you have any further comments analytic questions after the conference is finished for more information you can go to the developer slide quicktime if you have any up you wanna see where quicktime is in general you can go to the Apple side quicktime and for information you can go to the documentation side there is a QuickTime section area that has been updated just for this conference as I see us being present here there is documentation there is sample code that is only available to you if you go to the ABC side download place and you go to the QuickTime stuff so it should be available right now for you also we have mentioned this many times this morning there is a quick timeline out going on downstairs so if you have any questions for instance today is the special day for any audio questions all the engineers from the audio team will be down there are they loud today all day you can go down there is in the first floor Sacramento room there is also some assistance for content development if that's what you're interested in you