[gst-devel] Re： Re: re： Re: how to use qtdemux to demux h264 stream from MP4?

[zhangfei gao]

Hi, jp_liu 
   
  For avcC, the data struct is "len + data", no matter sps, pps or nal, so data could be parsed out from "len" information.
  
"codec_data" contains sps and pps.
qtdemux send h264 data by means of frame, which may contains several nals, they are all formated as "len + data".
They are translated as bitstreams.
  please check ffmpeg.
   
  Thanks 

jp_liu <jp_liu at astrocom.cn> 写道：
      zhangfei gao, Hello 
   
  My h264 decoder support say that:
  I believe MP4 uses the NAL format (Need to confirm) and hence doesn’t have the NAL Start codes. One needs to convert that to bytstream format because our decoders support only byte-stream format. Also one needs to do this while demuxing it from MP4 otherwise the information various slice positions would be lost. 
   
  So, How should I do?
   
  jp_liu, jp_liu at astrocom.cn">jp_liu at astrocom.cn
  2007-03-26 
    ----- Receiving the following content ----- 
  From: zhangfei gao 
  Receiver: gstreamer-devel 
  Time: 2007-03-22, 21:24:01
  Subject: [gst-devel]re： Re: how to use qtdemux to demux h264 stream from MP4?
  

  
  
    hi, jp_liu
   
  "h264.c" in ffmpeg has useful information of how to parse "codec_data" which get set_caps.
  "codec_data" has all the nal_length, sps data and pps data.
   
  Thanks
Jan Schmidt <thaytan at noraisin.net> 写道：
  jp_liu wrote:
> Hello, gstreamer-devel
> 
> How to use qtdemux to demux h264 stream from MP4?
> The demuxed h264 stream looks have no startcodes before every NAL
> Unit. So, Some key information ( such as: SPS PPS ....) is missed. It
> caused my H264 decoder can not decode the frame which demuxed by qtdemux .
> How can I solve this problem?
> 

I think the information your decoder is looking for is the stuff
provided by the 'codec_data' in the caps. This is the header information
that quicktime stores and provides separately from the actual data stream.

Regards,
Jan.

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