Recherche avancée

Sur d’autres sites (11940)

• avformat/rtpdec_jpeg : fix low contrast image on low quality setting

  24 mars 2016, par Ico Doornekamp

  avformat/rtpdec_jpeg : fix low contrast image on low quality setting
  Original mail and my own followup on ffmpeg-user earlier today :
  I have a device sending out a MJPEG/RTP stream on a low quality setting.
  
  Decoding and displaying the video with libavformat results in a washed
  
  out, low contrast, greyish image. Playing the same stream with VLC results
  
  in proper color representation.
  Screenshots for comparison :
    http://zevv.nl/div/libav/shot-ffplay.jpg
  
    http://zevv.nl/div/libav/shot-vlc.jpg
  A pcap capture of a few seconds of video and SDP file for playing the
  
  stream are available at
    http://zevv.nl/div/libav/mjpeg.pcap
  
    http://zevv.nl/div/libav/mjpeg.sdp
  I believe the problem might be in the calculation of the quantization
  
  tables in the function create_default_qtables(), the attached patch
  
  solves the issue for me.
  The problem is that the argument ’q’ is of the type uint8_t. According to the
  
  JPEG standard, if 1 <= q <= 50, the scale factor ’S’ should be 5000 / Q.
  
  Because the create_default_qtables() reuses the variable ’q’ to store the
  
  result of this calculation, for small values of q < 19, q wil subsequently
  
  overflow and give wrong results in the calculated quantization tables. The
  
  patch below uses a new variable ’S’ (same name as in RFC2435) with the proper
  
  range to store the result of the division.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/rtpdec_jpeg.c

• Live TV Stream to Android

  8 mai 2016, par Hd Dream

  I am new user on stackoverflow.
  I wrote you today to get answer and solution to my problem.
  I have input stream come from vlc. I need that all android connected to my network can watch stream in live in the same time like an online channel tv.
  I saw for this channel

  Code : Select all
  www.canal2international.net/live.php

  there is a same ts file is generated for each 45 second.

  I need to do the same but with a mp4 file that I insered on html5 video tag.
  for that I tried to convert my input stream with this cmd on ffmpeg

  Code : Select all
  ffmpeg -i 192.168.1.10:8620 -c:v libx264 -profile:v baseline -c:a aac -ar 44100 -ac 2 -b:a 128k -f segment -segment_time 45 -segment_format_options movflags=+faststart -segment_list D :\live\play.m3u8 -segment_list_size 2 D :\live\watch%03d.mp4

  I’m not satisfied. I can’t insert m3u8 file in html5 video tag because android don’t read it and his content.

  I tried another code that I can say little similar that the result of this page

  Code : Select all
  www.canal2international.net/live.php

  Code : Select all
  ffmpeg -i 192.168.1.10:8620 -hls_flags single_file D :\live\play.m3u8

  It generated two files, a ts and a m3u8.
  I know that html5 video tag can read ts file. Maybe there is a solution somewhere.

  The second way I don’t like in this code is ts file don’t read in real time. When I read file it begin from the first encoding.

  All android connected to my network must watch in real time !

  I don’t know how to solve my problem that’s why I write in thie forum.

  Thank you in advance for all your help !

• FFMPEG API and cropping

  24 juin 2016, par Jguillot

  I learned how to use FFMPEG API with dranger’s tutorial, and I implemented a video reader using the library SDL to display the video.

  I have a HD video 1280*720 (i only worked with mp4) and i want to select a VGA-screen anywhere in the HD video (I mean cropping a VGA screen in a HD video), recuperate the data and display it on screen.

  In the FFMPEG API, we can use the function av_picture_crop (here). I get a "yellow" overlay on the cropped video and my application crashes after fews seconds. Before posting here, i read here that the function wasn’t finish yet. But when i reading the code, i don’t find a way to finish it.
  This is a part of my code :

  AVFrame *pFrame = NULL;
  
  AVFrame *pFrameCropped = NULL;
  
  bmp = SDL_CreateYUVOverlay(CODEC_WIDTH, // width
  
                            CODEC_HEIGHT, // height
  
                            SDL_YV12_OVERLAY, // format
  
                            screen); // SDL_Surface to display
  
  
  
  
  
  sws_ctx = sws_getContext(CODEC_WIDTH, // src width
  
                          CODEC_HEIGHT, // src height
  
                          pCodecCtx->pix_fmt, // src img format
  
                          STREAM_WIDTH, // dest width, 
  
                          STREAM_HEIGHT, // dest height
  
                          AV_PIX_FMT_YUV420P, // dest img format
  
                          SWS_BILINEAR, // option to rescalling
  
                          NULL, //
  
                          NULL, //
  
                          NULL //
  
                          );
  
  
  
  while(
  
  av_read_frame(pFormatCtx, 
  
                  &packet)>=0) 
  
  {
  
  if(packet.stream_index==videoStream) 
  
  {
  
    avcodec_decode_video2(pCodecCtx,
  
                           pFrame,
  
                           &frameFinished,
  
                           &packet);
  
  
  
    if(frameFinished) 
  
    {
  
      SDL_LockYUVOverlay(bmp);
  
  
  
      av_picture_crop((AVPicture*)pFrameCropped,
  
                       (AVPicture*)pFrame,
  
                       (AVPixelFormat)pFrame->format,
  
                       150,
  
                       300);
  
      pict.data[0] = pFrameCropped->data[0];// "X"
  
      pict.data[1] = pFrameCropped->data[1];
  
      pict.data[2] = pFrameCropped->data[2];
  
  
  
      // pict.linesize == number of bytes per line 
  
      pict.linesize[0] = pFrameCropped->linesize[0];
  
      pict.linesize[1] = pFrameCropped->linesize[2];
  
      pict.linesize[2] = pFrameCropped->linesize[1];
  
  
  
      sws_scale(sws_ctx, // the scaling context previously created with sws_getContext()
  
                  (uint8_t const * const *)pFrameCropped->data, // Pointers to the planes of the source slice 
  
                  pFrame->linesize, // the array containing the strides for each plane of the source image 
  
                  0, // position in src img processed slice.  
  
                     // It's number (counted starting from zero) 
  
                     // in the image of the first row of the slice  
  
                  CODEC_HEIGHT, // source slice height. Number of rows in the slice
  
                  pict.data, // pointers to the planes of the destination image 
  
                  pict.linesize); // strides for each plane of the destination image 
  
  
  
      // Unlock SDL_Overlay
  
      SDL_UnlockYUVOverlay(bmp);
  
  }

  Get the compilation error :

  *** glibc detected *** ./HDtoVGA: corrupted double-linked list: 0x08d74e30 ***

  In the FFMPEG command line tool, we can crop a video, using vf_crop (here) but I don’t find how to implement the same function in my code.

  Do you have any hint to help me ?