[Matroska-devel] CodecSpecs

Santiago Jimeno sjimeno at ya.com
Thu Jan 6 00:01:45 CET 2011

I have not received any answer, so in accordance with my investigations I inform of that gotten for if this can help somebody. I to think that the data of CodecSpecs should be edited again with the purpose that they were more explicit.

AC3 and EAC3 in SymplyBlock (A3): follow ATSC a_52 - 2010 specifications. My error is that I waited that audio code was in the first track of the cluster, but it doesn't always happen this way.

Quicktime in Private data: follows MP4 specifications of stsd atom. But QDMC from AudioSampleEntry with size (4 bytes) and format (4 char) before, and QDM2 from frma box (52 bytes later).

DTS in SymplyBlock (A3): adds the whole header with included syncword (HD also).

New problem:  MLP and TrueHd
MLP: includes complete Header in SymplyBlock. But it doesn't add more data than the content in TrackEntry. 
TrueHd:  impossible for my to find the relationship between the data of SymplyBlock and the specifications.
Any suggestion about this?
Does somebody have an audio sample of TrueHd?

Regards. Santiago

  ----- Original Message ----- 
  From: Santiago Jimeno 
  To: matroska-devel at lists.matroska.org 
  Sent: Thursday, December 30, 2010 12:38 PM
  Subject: [Matroska-devel] CodecSpecs

  I am writing a program that reads information of audio files. Also it reads and writes the diverse Tags. It is centered specifically in the audio information. Now I am working with Matroska.

  As for audio information, specifications in CodecSpecs are quite clear in some cases (MPEG, Vorbis, MS/ACM, Flac, WavPack, etc)
  But in another cases it is not so well explained, although I have been able to write code:

  AAC-MP4: there it says that it is stripped from ADTS header. Really, in both cases of 2 or 5 bytes size it follows the specifications ISO-IEC 14496-1 Systems (AudioSpecificConfig). Another thing is that the first 2 bytes are common for ADTS and other formats.

  Real Audio: there is not information. Here, CodecPrivate follows the specifications of "MDPR" Media Properties -> Specific Data (audio/x-pn-realaudio or audio/x-pn-multirate-realaudio). Although in this case is contemplated the possibility of including "REAL/RALF" (Real Lossles), the specifications are possibly different: "audio/x-ralf-mpeg4-generic." But I have not been able to get the sample to study it with any program that encodes Matroska that I have been able to find.

  Maybe it would be interesting for other people to add this information in CodecSpecs

  Now the problems:
  AC3:  I have not been able to find in Block or CodecPrivate the mentioned Byte with fscod and frmsizecod data. 
  QuickTime:  In spite of their resemblance with AAC-MP4, I have not found the applied format to CodecPrivate data and CodecSpecs don't says anything about this.

  Can somebody inform me about these 2 problems?

  Now the suggestions:
  I miss the data of Bitrate and AudioSize. Apart of case when the codec specifies it (MPEG, MS/ACM) there is not bitrate information in any place. AudioSize can be easily calculated from bitrate. Also to the reverse, but then it would be necessary parsing all blocks.
  I know that it is not outstanding to decode the file but it is important for the information. There is not a place to write this information In the future? This can fill one byte or less inside of the big space filled for container Matroska 

  In a next message I will speak of my experience in Matroska Taging.

  Regards. Santiago


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