Historical solution for implicit encoder delay
Implicit encoder delay uses the most common delay of 2112 audio samples.
Overview
In the original AAC implementations, as stated above the common practice was to propagate the encoder delay in the provided AAC bitstream. With these original implementations, the most common delay used was 2112 audio samples. An AAC bitstream would therefore generally be 3 AAC packets larger than what was theoretically required by the original signal.
A playback implementation would then need to discard these first 2112 silent samples from the decoded output since they contain none of the original source audio data; these samples are an artifact of the encoding/decoding process.
Because there was no explicit way to represent the extent of the priming or remainder samples with the first implementations of an AAC bitstream, QuickTime assumed that the AAC bitstream always contained an encoding delay with a fixed number of samples. A fixed encoder delay of 2112 samples was chosen because at that time this was the common encoding delay used, for various reasons, by most of the shipping implementations of AAC encoders (commercial and otherwise).
In summary, the historical technique to handle the timing and synchronization problem is to assume an implicit 2112 sample standard encoder delay in AAC data streams and indicate start time—the first media sample or AAC packet—in the sound track edit list (see Edit list atom ('elst')) at the start of encoder delay.