---
title: MEVideoDecoder
framework: MediaExtension
role: symbol
role_heading: Protocol
platforms: [macOS 14.0+]
path: mediaextension/mevideodecoder
---

# MEVideoDecoder

A protocol that defines the requirements for a video decoder.

## Declaration

```swift
protocol MEVideoDecoder : NSObjectProtocol
```

## Overview

Overview This protocol provides an interface for Video Toolbox to create and interact with MediaExtension video decoders. MEVideoDecoder objects are always instantiated by Video Toolbox. note: Developers who wish to build MediaExtension video decoders using this API need to include a Video decoder entitlement, provisioning profile, and specialized dictionary in their Info.plist file when building their extensions. For more information, see Entitlements, Create a development provisioning profile, and Video decoder property list dictionary Once a user installs and runs the host app, embedded video decoder extensions become available to any app on the user’s system that opts in to using them by calling VTRegisterProfessionalVideoWorkflowVideoDecoders(). important: MEVideoDecoder objects run in a sandboxed process without access to the filesystem, network, and other kernel resources. The following sections explain the video decoder life cycle and performing decoding operations. Creating a video decoder The first time Video Toolbox opens a decoder in a process, it creates an instance of the MEVideoDecoderExtension factory object. It then calls its makeVideoDecoder(codecType:videoFormatDescription:videoDecoderSpecifications:pixelBufferManager:) method for each decoder instance it needs. A decoder can evaluate the CMVideoCodecType and CMVideoFormatDescription that the system provides and confirm whether it can decode the specified format. If the decoder can’t decode the format, the factory routine needs to return the error MEError.Code.unsupportedFeature. This sequence of events happens within VTDecompressionSessionCreate(allocator:formatDescription:decoderSpecification:imageBufferAttributes:outputCallback:decompressionSessionOut:). Configuring a pixel buffer Once instantiated, a decoder can call back to the provided MEVideoDecoderPixelBufferManager object to notify Video Toolbox of its output CVPixelBuffer requirements. It can make these calls multiple times if output requirements change in response to properties receiving new values or due to observed bitstream characteristics. Querying and setting properties Properties can receive queries or new values on the decoder at any time, before, during or after frame decode, unless otherwise noted. These calls generally correspond to VTSessionSetProperty(_:key:value:) and VTSessionCopyProperty(_:key:allocator:valueOut:) calls on the VTDecompressionSession which opened the decoder. There may be cases where Video Toolbox directly sets or queries properties as well. Decoding frames The framework serializes calls to decodeFrame(from:options:completionHandler:) and doesn’t send a new frame to the decoder until the last decodeFrame(from:options:completionHandler:) returns, unless decoding happens asynchronously. These calls correspond to VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:infoFlagsOut:outputHandler:) calls on the owning VTDecompressionSession. Video decoders need to write their output frames into CVPixelBuffer objects allocated by the MEVideoDecoderPixelBufferManager object’s makePixelBuffer() method. Obtaining pixel buffers from any other source may degrade performance or result in other issues. If the decoder’s internal decoding queue is full and it can’t decode more frames, its isReadyForMoreMediaData property value returns false. It returns true once the decoder can start accepting new frames again. This generally occurs after an earlier asynchronous frame completes. Handling format description changes If a change occurs in the format description on incoming CMSampleBuffer objects, Video Toolbox calls canAccept(_:) to confirm whether the decoder can transition to the new format description. If that method response is false, the system usually closes the decoder and creates a new instance for the changed format description. A call to VTDecompressionSessionCanAcceptFormatDescription(_:formatDescription:) can trigger a call of canAccept(_:), or Video Toolbox calls this method if it sees a format description change on incoming CMSampleBufferRef objects.

## Topics

### Inspecting a video decoder

- [contentHasInterframeDependencies](mediaextension/mevideodecoder/contenthasinterframedependencies.md)
- [recommendedThreadCount](mediaextension/mevideodecoder/recommendedthreadcount.md)
- [actualThreadCount](mediaextension/mevideodecoder/actualthreadcount.md)
- [supportedPixelFormatsOrderedByQuality](mediaextension/mevideodecoder/supportedpixelformatsorderedbyquality.md)
- [reducedResolution](mediaextension/mevideodecoder/reducedresolution.md)
- [pixelFormatsWithReducedResolutionDecodeSupport](mediaextension/mevideodecoder/pixelformatswithreducedresolutiondecodesupport.md)
- [producesRAWOutput](mediaextension/mevideodecoder/producesrawoutput.md)
- [isReadyForMoreMediaData](mediaextension/mevideodecoder/isreadyformoremediadata.md)

### Decoding frames

- [canAccept(_:)](mediaextension/mevideodecoder/canaccept(_:).md)
- [decodeFrame(from:options:completionHandler:)](mediaextension/mevideodecoder/decodeframe(from:options:completionhandler:).md)
- [MEDecodeFrameStatus](mediaextension/medecodeframestatus.md)

### Extension requirements

- [Video decoder property list dictionary](mediaextension/video-decoder-property-list-dictionary.md)
- [Video decoder entitlement](mediaextension/video-decoder-entitlement.md)

## Relationships

### Inherits From

- [NSObjectProtocol](objectivec/nsobjectprotocol.md)

## See Also

### Video decoders

- [Supporting custom media formats and decoders](mediaextension/supporting-custom-media-formats-and-decoders.md)
- [MEVideoDecoderExtension](mediaextension/mevideodecoderextension.md)
- [MEDecodeFrameOptions](mediaextension/medecodeframeoptions.md)
- [MEVideoDecoderPixelBufferManager](mediaextension/mevideodecoderpixelbuffermanager.md)
- [Video decoder property list dictionary](mediaextension/video-decoder-property-list-dictionary.md)
- [Video decoder entitlement](mediaextension/video-decoder-entitlement.md)