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• Demuxing and decoding raw RTP with libavformat

  8 février 2023, par kevmo314

  I'm implementing a pipeline where I receive inbound RTP packets in memory but I'm having trouble figuring out how to set up libavformat to handle/unwrap the RTP packets.

  


  I have all relevant information about the underlying codec necessary but since it's h264 I cannot simply strip the RTP header trivially. I create the input context with goInputFunction writing one packet per invocation.

  


  void *readbuf = av_malloc(1500);
AVIOContext *avioreadctx = avio_alloc_context(readbuf, 1500, 0, transcoder, &goInputFunction, NULL, NULL);
AVFormatContext *inputctx = avformat_alloc_context();
inputctx->pb = avioreadctx;
inputctx->flags |= AVFMT_FLAG_CUSTOM_IO;


  


  When I open it with avformat_open_input(&inputctx, NULL, NULL, NULL) it repeatedly calls the read function but doesn't actually progress. I suspect because the RTP stream itself does not have enough information to fully describe the codec ? If I leave this open out, then av_read_frame(inputctx, input_packet) down the road segfaults, I'm guessing because the input context is uninitialized.

  


  So to my question, is it possible to set the codec details that the SDP would typically set, but manually ?

  


  I'm looking for an example of how to manually configure the AVFormatContext to consume RTP packets without an SDP and setting up a UDP port listener.

  


• “Hook” libMMS to FFmpeg for iPhone Streaming

  8 novembre 2011, par Xie Xingwei

  These days, I was researching the software architechture for iPhone Streaming (Base on MMS protocol).

  As we know, in order to playback MMS audio stream, we should call libMMS to read wma stream data from remote media server, and then call FFmpeg to decode the stream data from wma format into PCM data buffer, and finally, enqueue the PCM data buffer into iPhone’s audioqueue to generate real sound.

  The introduction above just describe the working process of iPhone streaming. If we only need to implement this simple functionality, that is not difficult. Just follow the introduction above to call libMMS, FFMpeg and audioqueue step by step, we can achieve the streaming function. Actually, I have implemented the code last week.

  But, what I need is not only a simple streaming function ! I need a software architechture makes FFmpeg accessing libMMS just like accessing local filesystem !

  Does anybody know how to hook the libMMS interfaces like mms_read/mms_seek onto FFmpeg filesystem interfaces like av_read_frame/av_seek_frame ?

• FFMPEG + SDL : How To Show Multi Frames In Separate Region ?

  19 mai 2014, par user3051473

  I’m using ffmpeg and SDL to develop an camera monitor APP and I want to show four separate streams at the same time(via four rtsp source). As following figure out :

  Now I achieve this by setting the SDL display region, and I identify different display region by using the different SDL_Rect identifying by the variable i(from 1 - 4).

  But this cause the efficient problem. For every region, I need to scale to the whole screen and lock/unlock screen, then display.

  I’m wondering that, Can I merge 4 different AVFrame(come from REG1 - REG4) into the whole picture and then show this picture ?

  Hope that the describe about is detail enough for you to konw my problem.
  Also thanks for your help.

  -------------------
  
  -        -        -
  
  -  REG1  -  REG2  -
  
  -        -        -
  
  -------------------
  
  -        -        -
  
  -  REG3  -  REG4  -
  
  -        -        -
  
  -------------------
  
  
  
  public void ShowFrame(AVFrame *pFrame, AVCodecContext *pCodecContext)
  
  {
  
      SDL_LockYUVOverlay(pBmp);
  
      AVPicture pict;
  
  
  
      // TODO scale pFrame to pict
  
      // ...
  
  
  
      SDL_UnlockYUVOverlay(pBmp);
  
  
  
      // WIDTH and HEIGHT represent the whole screen size
  
      SDL_Rect rect;
  
      rect.x = (WIDTH / 2) * (i % 2);
  
      rect.y = (HEIGHT / 2) * (i > 1 ? 1: 0);
  
      rect.w = WIDTH / 2;
  
      rect.h = HEIGHT / 2;
  
      SDL_DisplayYUVOverlay(pBmp, &rect);
  
  }