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• Why MP4 generated through FFmpeg API can't be played in the Windows Media Player ?

  2 septembre 2021, par James

  I encoded some frames into a MP4 using FFmpeg API, but the MP4 could't be played in the Windows Media Player.

  


  By comparison with the normal MP4 using ffprobe, I found that the FOURCC of the problematic MP4 is 'H264' while the normal MP4 is 'AVC1'.
According to H.264 Video Types, 'AVC1' has start codes but 'H264' hasn't.I also learned that we shoud manually add sps and pps before H.264 stream when demuxing a MP4.

  


  Now I don't know how to add start code or sps/pps to my MP4, please give me a hand.
How I should do to generate a MP4 which can be played in the Windows Media Player ?

  


  I have tried to add h264 bitstream filter but it didn't work. The code below :

  


   AVBitStreamFilterContext *bsfc = NULL;
bsfc = av_bitstream_filter_init("h264_mp4toannexb");
if (bsfc == NULL) {
            printf("bsfc is NULL\n");
}
        
av_bitstream_filter_filter(bsfc, codec_ctx, NULL, &(pkt->data), &(pkt->size), pkt->data, pkt->size, 0);

av_bitstream_filter_close(bsfc);


  


  After a lot of trying, I found that manually adding sps and pps to codec_ctx->extradata effective :

  


  unsigned char sps_pps[23] = { 0x00, 0x00, 0x00, 0x01, 0x67, 0x64, 0x00, 0x29, 0xac, 0x1b, 0x1a, 0x12, 0xe0, 0x51, 0x90,
                              0x00, 0x00, 0x00, 0x01, 0x68, 0xea, 0x43, 0xcb };
codec_ctx->extradata_size = 23;
codec_ctx->extradata = (uint8_t*)av_malloc(23 + AV_INPUT_BUFFER_PADDING_SIZE);
if (codec_ctx->extradata == NULL) {
    printf("could not av_malloc the video params extradata!\n");
    ERR_NULL_EXIT
    }
memcpy(codec_ctx->extradata, sps_pps, 23);


  


  The code above refered to an answer of @szatmary

  


  Now generated MP4 can be played in Windows Media Player. But a new question emerges because I don't konw what correct value of sps/pps is. It cause that the width and height of frame presented in the Windows Explorer is incorrect. So I need to set the correct sps/pps. I also read the document of sps/pps but get confused because some parameters have variable bits. So can anybody tell me how to set the sps/pps correctly ?

  


• Retrieving stdout from subprocess in Windows

  6 août 2017, par Cryptite

  I can call FFmpeg with subprocess.Popen and retrieve the data I need, as it occurs (to get progress), but only in console. I’ve looked around and seen that you can’t get the data "live" when running with pythonw. Yet, waiting until the process finishes to retrieve the data is moot, since I’m trying to wrap a PyQT GUI around FFmpeg so I can have pretty progress bars and whatnot. So the question is, can you retrieve "live" data from a subprocess call when using pythonw ?

  I haven’t tried simply compiling the application with py2exe yet as a windows application, would that fix the problem ?

• FFmpeg libraries on Windows - Undefined References

  26 novembre 2018, par Gomes

  I am trying to use FFmpeg libraries available from here under Windows 10 (64 bits). I downloaded version=20181126-90ac0e5, architecture=Windows-64, Linking=Dev. There are 3 folders inside that FFmpeg folder : examples, lib and include.
  To use these libraries I copied the contents of the "include" folder to the "include" folder of my MinGW installation. I also copied the contents of the "lib" folder to the "lib" folder of MinGW.
  I try to compile the decode_video.c example that comes inside the examples folder with the following way :

   gcc decode_video.c -o decode_video.exe -lavcodec -lavutil -lavformat -lm

  The compiler gives me these undefined references :

   undefined reference to `avcodec_send_packet'
  
   undefined reference to `avcodec_receive_frame'
  
   undefined reference to `av_packet_alloc'
  
   undefined reference to `avcodec_find_decoder'
  
   undefined reference to `av_parser_init'
  
   undefined reference to `avcodec_alloc_context3'
  
   undefined reference to `avcodec_open2'
  
   undefined reference to `av_frame_alloc'
  
   undefined reference to `av_parser_parse2'
  
   undefined reference to `av_parser_close'
  
   undefined reference to `avcodec_free_context'
  
   undefined reference to `av_frame_free'
  
   undefined reference to `av_packet_free'

  I would like to know what I am doing wrong here. Any guidance is very welcome.