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• Need help on handling MPEG4V1 data

  31 janvier 2021, par Gediminas

  I'm in situation where I need to get a chunk of MPEG4V1 (Microsoft MPEG-4 VKI
Codec V1) data located in the beginning of a packet (that was sent by some DVR unit).

  



  Packet structure looks something like this :

  



  

  • Compressed MPEG4 data.

  


  • Long integer - Number of events and tripwires.

  


  • Long integer - Number of events.

  


  • Event - Event's sequence.

  


  • Long integer - Number of tripwires.

  


  • Tripwire - Tripwires sequence.

  


  • Long integer - Cyclical redundant code (CRC).

  


  



  So there is no indication of how to know where does the MPEG4 data ends (Or is there ?),
and from where should I start reading this additional data like "Number of events and tripwires" and etc...

  



  I uploaded two packet's so you could see how the actual data looks like :
recvData1.txt,
recvData2.txt.

  



  I've tried to decode those packets using FFmpeg library with avcodec_decode_video function and by removing byte by byte from the end of my recvData buffer in a hope for any results,
  
but FFmpeg just allways returned with an error messages like this :

  



  


  "[msmpeg4v1 @ 038865a0] invalid startcode",
 "[msmpeg4v1 @ 038865a0] header damaged".

  


  



  I'm not that good specialist on knowing of how does the MPEG4 works from the inside,
but judging by the error messages it's clearly seen that I'm missing some data for decoding at the start of the buffer.

  



  So I'm not sure of what part / kind of MPEG data I'm getting here..
  
Maybe it's some kind of MPEG's "frame" data with it's "end" indication or something ?

  



  I've even compared the start of my recvData buffer to some of MPEG4V1 encoded video files I found on the net "http://www.trekmania.net/clips/video_clips4.htm" to check if the start of my buffer really contains the MPEG data ..and not some kind of DVR vendor specific stuff..

  



  And I noticed that there are about 20bytes of data 
(at the start of my packet data, and in .avi files right after about 180bytes..) 
that looks like some kind of header or something..

  



  Please check this image : "http://ggodis.gamedev.lt/stackOverflow/recvData.jpg"

  



  Maybe someone knows what this part of MPEG4V1 data represents ?

  



  P.S. ..I've checked the CRC values for my received packets and they were correct..

  


• Need help on handling MPEG4V1 data

  14 septembre 2011, par Gediminas

  I'm in situation where I need to get a chunk of MPEG4V1 (Microsoft MPEG-4 VKI
  Codec V1) data located in the beginning of a packet (that was sent by some DVR unit).

  Packet structure looks something like this :

  • Compressed MPEG4 data.
  • Long integer - Number of events and tripwires.
  • Long integer - Number of events.
  • Event - Event's sequence.
  • Long integer - Number of tripwires.
  • Tripwire - Tripwires sequence.
  • Long integer - Cyclical redundant code (CRC).

  So there is no indication of how to know where does the MPEG4 data ends (Or is there ?),
  and from where should I start reading this additional data like "Number of events and tripwires" and etc...

  I uploaded two packet's so you could see how the actual data looks like :
  recvData1.txt,
  recvData2.txt.

  I've tried to decode those packets using FFmpeg library with avcodec_decode_video function and by removing byte by byte from the end of my recvData buffer in a hope for any results,
  but FFmpeg just allways returned with an error messages like this :

  "[msmpeg4v1 @ 038865a0] invalid startcode",
  "[msmpeg4v1 @ 038865a0] header damaged".

  I'm not that good specialist on knowing of how does the MPEG4 works from the inside,
  but judging by the error messages it's clearly seen that I'm missing some data for decoding at the start of the buffer.

  So I'm not sure of what part / kind of MPEG data I'm getting here..
  Maybe it's some kind of MPEG's "frame" data with it's "end" indication or something ?

  I've even compared the start of my recvData buffer to some of MPEG4V1 encoded video files I found on the net "http://www.trekmania.net/clips/video_clips4.htm" to check if the start of my buffer really contains the MPEG data ..and not some kind of DVR vendor specific stuff..

  And I noticed that there are about 20bytes of data
  (at the start of my packet data, and in .avi files right after about 180bytes..)
  that looks like some kind of header or something..

  Please check this image : "http://ggodis.gamedev.lt/stackOverflow/recvData.jpg"

  Maybe someone knows what this part of MPEG4V1 data represents ?

  P.S. ..I've checked the CRC values for my received packets and they were correct..

• aacdec : don’t return frames without data

  12 mai 2015, par Andreas Cadhalpun

  aacdec : don’t return frames without data
  Since commit 676a395a aac->frame->data is not necessarily allocated at
  
  the end of aac_decode_frame_int if avctx->channels is 0.
  In this case a bogus frame without any data, but non-zero nb_samples is
  
  returned.
  Signed-off-by : Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/aacdec.c