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EssenceDescriptor and EssenceData for embedded audio

Developers
pieterb
2013-08-09
2013-08-09
  • pieterb
    pieterb
    2013-08-09

    Hello everyone,

    I have some questions about embedding audio essence into AAF.
    Suppose, I have an audio file (WAV or BWF) and I want to put the essence data in the AAF file.

    1) Which EssenceDescriptor do I use? The only difference between a WAV file and a BWF file is an extra "bext" chunk. According to AAF documentation, I should use PCM Descriptor for BWF's, and WAVEDescriptor for WAV. However, there are applications that use WAVEDescriptor for BWF.
    2) Which data has to be present in the EssenceData object? Only the raw sample data (so the content of the "data" chunk) or the complete RIFF data?
    3) The WAVEDescriptor must contain a copy of the WAV header. Does this mean:
    * All RIFF chunks before the data chunk, with or without the data chunk ID and data chunk size, or
    * All RIFF chunks before and after the data chunk, with or without the data chunk ID and data chunk size, or
    * Only the RIFF and fmt chunk, with or without the data chunk ID and data chunk size
    In practice, I've seen that usually the EssenceData contains only raw sample data for PCMDescriptor, but the complete WAV information for WAVEDescriptor.

    Furthermore, I don't quite understand why there's so much difference between the WAVEDescriptor object and the PCMDescriptor object. The only difference is the extra "bext" information, which aren't even properties of the PCMDescriptor itself.

    Thanks in advance,

    Pieter