Recherche avancée

Sur d’autres sites (5898)

• quickdraw : Switch to greedy parsing

  18 avril 2015, par Vittorio Giovara

  quickdraw : Switch to greedy parsing
  Quickdraw packs data as a series of codes that the application is supposed
  
  to handle, but it does not define any order in which they might appear.
  
  Since it’s unfeasible to support *all* opcodes defined by the spec,
  
  only handle well-known blocks containing video data and ignore any unknown
  
  or unsupported ones.
  Move palette loading and rle decoding to separate functions to resue them
  
  in other blocks and drop format initialization in init since it can
  
  support more formats than pal8.
  Validate width and height.
  

  • [DBH] libavcodec/qdrw.c

• Different results in capturing a video, convert to frames then convert to the video again

  30 mai 2019, par Sam

  I’m working on an idea and in the first stage, I have one requirement which I capture a video and convert this video to a series of frames(pictures) and then convert frames to another video again.
  For reaching this goal I got three tasks :

  1. Capture a video :
     I have done this step by following ffmpeg command :

     ffmpeg -f gdigrab -framerate 10 -i desktop d:\video_1.avi

  2. Covert the generated video to images :

     ffmpeg -i d:\video_1.avi -vf fps=10  d:\frames\frame_%04d.bmp 

  3. Finally, convert images to another video again :

     ffmpeg -framerate 10 -i d:\frames\frame_%04d.bmp  d:\out_video_1.avi

  When I compared video_1.avi and out_video_1.avi I saw these videos had different size. The difference is about 30 kb in the six-second video.
  I compared two videos by Matlab and saw two videos are really different.

  I need to be sure that two videos are the same for continuing to work on other stages of my idea but I was stuck at this stage.

• Multiple frames lost if I use av_read_frame in FFmpeg

  12 juin 2015, par Krishna

  I have an HEVC sequence with 3500 frames and I am writing a decoder for reading it (read frame by frame and dump to yuv). In my main(), I have a for loop that calls a decoder() 3500 times (I am assuming at this stage that the main() knows how many frames there are).

  So, for every call to decoder(), I need a complete frame to be returned. This is what the decoder() looks like..

  bool decode(pFormatCtx, pCodecCtx)
  
  {
  
      int gotaFrame=0;
  
  
  
      while (gotaFrame==0) {
  
  
  
          printf("1\t");
  
  
  
          if ( !av_read_frame(pFormatCtx, &packet) ) { 
  
              if(packet.stream_index==videoStreamIndex) {
  
  
  
                  // try decoding
  
                  avcodec_decode_video2(pCodecCtx, pFrame, &gotaFrame, &packet);
  
  
  
                  if (gotaFrame) {  // decode success.
  
  
  
                      printf("2\t");
  
  
  
                      // dump to yuv ... not shown here. 
  
  
  
                      // cleanup
  
                      av_frame_unref(pFrame);
  
                      av_frame_free(&pFrame);
  
                      av_free_packet(&packet);
  
  
  
                      return true;
  
                  }
  
              }
  
          }
  
      }
  
  }

  The behavior is like this : 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 2 1 2 ...... it looks like it reads several frames before decoding one ? The first frame is an I-frame, so shouldn’t that be decoded right away ?

  With this code, I end up losing the several frames (indicated by the series of 1s). Can someone help me out here ? Is there something I am doing wrong in my code ?

  Update : the test clip is video-only. No audio.