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• Why the source order matters on working with multiple media sources in a single AVFormatContext ?

  24 avril 2024, par Mehmet YILMAZ

  avformat_open_input() deletes the AVFormatContext* and returns -6 when the source order changes.

  


  I am trying to open multiple media sources dynamically with different(mixed) formats and codecs in a single context (AVFormatContext).

  


  My media sources are a BlackMagic DeckLink Duo SDI input as first source and an mp4 file or rtsp stream as second.

  


  When I order to open (avformat_open_input()) the source 2 (RTSP or MP4 file) at first and then open the BlackMagic DeckLink Duo, proceed as expected.

  


  But when I change the order, and first open the DeckLink and then try to open RTSP stream or MP4 file, as I inspected in the step debugger ; AVFormatContext* deleting in the av_open_input() function and it returns -6 as result.

  


  Please find the simple error reproduction code snappet below ;

  


  AVFormatContext* context{avformat_alloc_context()};
const char* url_source1{"DeckLink Duo (1)"};
const AVInputFormat* format_source1{av_find_input_format("decklink")};

const char* url_source2{"http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"};

// Open the first media input
int result = avformat_open_input(&context, url_source1, format_source1, NULL);

if(result < 0) {
  exit(1);
}

// Open the second media input
// This function in current order deletes the context and returns -6
result = avformat_open_input(&context, url_source2, NULL, NULL);
if(result < 0) {
  exit(1);
}

// Since the context has been deleted in previous step, segmentation fault accours here!
result = avformat_find_stream_info(context, NULL);
if(result < 0) {
  exit(1);
}

std::cout << "Total number of streams: " << context->nb_streams << std::endl;



  


  But When I change the order and call the avformat_open_input() first for the mp4 file and then the DeckLink device as following it proceed as expected, no error.

  


  AVFormatContext* context{avformat_alloc_context()};
const char* url_source1{"DeckLink Duo (1)"};
const AVInputFormat* format_source1{av_find_input_format("decklink")};

const char* url_source2{"http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"};


// Open the second media input
int result = avformat_open_input(&context, url_source2, NULL, NULL);
if(result < 0) {
  exit(1);
}


// Open the first media input
result = avformat_open_input(&context, url_source1, format_source1, NULL);

if(result < 0) {
  exit(1);
}


result = avformat_find_stream_info(context, NULL);
if(result < 0) {
  exit(1);
}

std::cout << "Total number of streams: " << context->nb_streams << std::endl;



  


• ffmpeg pipe to mediainfo

  16 octobre 2017, par Macheneso R.

  I need to get infos from the raw h264 track of a mkv file.

  Some times ago, I used to extract the h264 raw stream, and analyze it by itself.

  now, I would like to limit the disk usage, avoiding the extract process, so there are 2 choices :

  • use ffmpeg to pipe h264 to mediainfo

  • use a sort of ramdisk

  I tried

  ffmpeg -i original.mkv -map 0:v:0 -c copy -bsf:v h264_mp4toannexb -f h264 - | mediainfo -

  but it returns none

  where am I wrong ?

• How to encode a picture into H264 using x264 API ?

  23 novembre 2011, par cmm427

  I encode a picture following the link How to encode series of images into H264 using x264 API ? (C/C++), but every time x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out) returns 0.