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• libvlc vs FFMPEG for export video frame by frame

  3 décembre 2014, par Alexander

  I trying to mixing different videos and save them to another. I play video frame by frame and wait each time for mixing with OpenGL and coding. First I used DirectShow for this and it was awfully. Then I tried to use VLC and I had the same problems. Do you know any other library that can help me ? Maybe FFMPEG ?

  I try to use two approach in VLC. First. 1) set position 2) play 3) pause 4) get frame

  All was ok for some format like AVI or MP4. But some videos like MPG cannot set correctly at the needed position. And some videos like MTS and M2TS had bad frame after pause. So all frames was bad if we stopped video each frame.

  Second approach. Start to play from beginning and try to convert frames. But I cannot make it so fast how is decoding video. So I need in RAM memory or disk memory for saving without stopping. But it is bad for big videos.

  Can FFMPEG or something different help me ?

• Revision c0e561d15e : Fix a crash in vpxdec If the codec fails to return a frame on the second frame

  7 juin 2013, par John Koleszar

  Changed Paths :
   Modify /vpxdec.c

  
  
  Fix a crash in vpxdec

  If the codec fails to return a frame on the second frame (as in a VP8 alt-ref,
  then img will be a null pointer and dereferencing it while trying to write
  the color format (again) will crash.

  Change-Id : Ie48710d4c5715f532d453c879c71c20ccdeb81cc

• How to read any frame while having frame number using ffmpeg av_seek_frame()

  29 octobre 2016, par P Akhtar

  int64_t timeBase;
  
  timeBase = (int64_t(pavStrm-> time_base.num) * AV_TIME_BASE) / int64_t(pavStrm->time_base.den);
  
  int64_t seekTarget = int64_t(iFrameNumber) * timeBase;
  
  av_seek_frame(fmt_ctx, -1, seekTarget, AVSEEK_FLAG_FRAME);

  here I want to read next 5 frame after iFrameNumebr

  for(int iCnt = 0; iCnt <= 4; iCnt++)
  
  {
  
      iRet = av_read_frame(fmt_ctx, &pkt);
  
          do 
  
          {
  
              ret = decode_packet(&got_frame, 0);
  
              if (ret < 0)
  
                  break;
  
              pkt.data += ret;
  
              pkt.size -= ret;
  
  
  
          }while (pkt.size > 0);
  
      av_free_packet(&pkt);
  
  }
  
  
  
  static int decode_packet(int *got_frame, int cached)
  
  {
  
  int ret = 0;
  
  int decoded = pkt.size;
  
  *got_frame = 0;
  
  
  
  if (pkt.stream_index == video_stream_idx)
  
  {
  
      /* decode video frame */
  
      ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
  
  }

  when i am using AVSEEK_FLAG_BACKWARD its return 5 packet and 5 frame first two is blank but correct.

  when i am using AVSEEK_FLAG_FRAME its return 5 packet and 3 frame which are not first 3 frame its return specific frame from video.

  for any iFrameNumber

  so please help me how to get frame while having frame number and what is exact value of seektarget 3rd param of av_seek_frame()

  also I have problem while converting frame to rgb24 format