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• Encoding with FFMPEG stretches frames

  24 août 2017, par micropro.cz

  I am trying to encode video with FFMPEG into H.265, but I have a problem with a weird stretching. Input video is 1920x1080 and output has the same resolution, but when I compare both images on same timestamp, encoded video seems to be stretched by few pixels (it is visibly wider on both sizes despite the fact resolution is same). It seems that this stretching introduces ugly bluriness in whole video. It seems like FFMPEG crop few pixels from left and right (probably black pixels at the edge of video) and stretches content to fill those missing pixels and preserve same resolution.

  I did not find any way how to disable this behavior. I tried to change encoder from x265 to x264 to see if that is the problem, but result was still stretched.

  I used this command line parameters :

  ffmpeg -i input.mkv -c:v libx265 -preset medium -crf 23 -t 30 output.mp4

  -t 30 is there to test result visual quality on small sample of length 30 seconds.

  Does anyone have any idea why this happens and how to fix it ? Most visual quality is lost because of this deformation and not because of recompression, which I proved by encoding with -crf 0, which is basically lossless and result was still blurred.

  EDIT : Link to full console output : https://pastebin.com/gpMD5Qec

• ffmpeg does not decode some h264 streams

  12 janvier 2016, par Andrey

  I have some ip of cameras on the local network.I receive video stream with live555 library (I took testRtspClient as a basis) and decode frames with ffmpeg (avcodec_decode_video2). Everything perfectly works.
  Problems begin when I try to decode a stream from an internet.

  The first problem - some packets lost, so defects appears. But it’s not a problem. Problem - after stop and start video stream it is necessary to wait for about 5 minutes of streaming before ffmpeg is able to decode something from the same ip camera. If packets doesn’t lost then everithing ok.

  The second problem - there is camera which sends video with resolution 2048х1538. The frame of such resolution is sent by several packets. live555 normally brings together them but when the frame is transferred to the decoder, the decoder returns the packet length, but got frame always 0.

  Here some my code :

  #define RECEIVE_BUFFER_SIZE 1000000
  
  AVCodecContext* avCodecContext; //definition
  
  AVFrame *frame;  //definition
  
  ...
  
  //init code
  
  _fReceiveBuffer = new uint8_t[RECEIVE_BUFFER_SIZE+512]; //buffer to receive frame
  
  ZeroMemory(_fReceiveBuffer, RECEIVE_BUFFER_SIZE + 512); //zeros
  
  _bufferSize = RECEIVE_BUFFER_SIZE * sizeof(uint8_t); //buffer size
  
  
  
  static const  uint8_t startCode[4] = { 0x00, 0x00, 0x00, 0x01 }; //this is for 0 0 0 1
  
  //before frame will transfer to decoder
  
  memcpy(_fReceiveBuffer, (void*)startCode, sizeof(uint8_t)* 4);
  
  _fReceiveBuffer += sizeof(sizeof(uint8_t)* 4);
  
  _bufferSize -= sizeof(sizeof(uint8_t)* 4);
  
  
  
  AVCodec *codec = avcodec_find_decoder(AV_CODEC_ID_H264); //find codec
  
  
  
  avCodecContext = avcodec_alloc_context3(codec); 
  
  avCodecContext->flags |= AV_PKT_FLAG_KEY;
  
  avcodec_open2(avCodecContext, codec, NULL);
  
  
  
  frame = av_frame_alloc();
  
  
  
  //frame
  
  void DummySink::afterGettingFrame(unsigned frameSize, unsigned numTruncatedBytes,
  
  struct timeval presentationTime, unsigned durationInMicroseconds) {
  
  
  
  if (strcmp(fSubsession.codecName(), "H264") == 0)
  
  {
  
      //code from onvif device manager
  
      static const uint8_t startCode3[] = { 0x00, 0x00, 0x01 };
  
      static const uint8_t startCode4[] = { 0x00, 0x00, 0x00, 0x01 };
  
      auto correctedFrameSize = frameSize;
  
      auto correctedBufferPtr = fPlObj->_fReceiveBuffer;
  
      if (frameSize < sizeof(startCode4) || memcmp(startCode4, correctedBufferPtr, sizeof(startCode4)) != 0){
  
          if (frameSize < sizeof(startCode3) || memcmp(startCode3, correctedBufferPtr, sizeof(startCode3)) != 0){
  
              correctedFrameSize += sizeof(uint8_t)* 4;
  
              correctedBufferPtr -= sizeof(uint8_t)* 4;
  
          }
  
      }
  
  
  
      ProcessFrame(correctedBufferPtr, correctedFrameSize, presentationTime, durationInMicroseconds);
  
  }
  
  continuePlaying();
  
  }
  
  
  
  void DummySink::ProcessFrame(unsigned char* framePtr, int frameSize, struct timeval presentationTime, unsigned duration)    {
  
  
  
  AVPacket avpkt;
  
  av_init_packet(&avpkt);
  
  avpkt.data = framePtr;
  
  avpkt.size = frameSize;
  
  while (avpkt.size > 0) {
  
      int got_frame = 0;
  
  
  
      int len = avcodec_decode_video2(avCodecContext, frame, &got_frame, &avpkt);
  
      if (len < 0) {
  
          //TODO: log error
  
          return;
  
      }
  
      else if (got_frame == 0)
  
      {
  
  //I tried this code, bacause "codecs which have the AV_CODEC_CAP_DELAY capability set have a delay between input and output"
  
  //but it didn't help
  
          /*AVPacket emptyPacket;
  
          av_init_packet(&emptyPacket);
  
          emptyPacket.data = NULL;
  
          emptyPacket.size = 0;
  
          emptyPacket.stream_index = avpkt.stream_index;
  
          len = avcodec_decode_video2(avCodecContext, frame, &got_frame, &emptyPacket);
  
          if ( got_frame == 1) goto next;*/
  
          return;
  
      }
  
  next:
  
      //... here code for view with DirectDraw - everithing ok with it
  
      avpkt.size -= len;
  
      avpkt.data += len;
  
  }
  
  }

  I alsa tried to send frame to decoder with sps and pps information :

  0 0 0 1 sps 0 0 0 1 pps 0 0 0 1 frame

  but it is not help.

  Interesting that avcodec_decode_video2 does not return frame with second problem (return all size of frame), but width and height in avCodecContext are set correctly. I can’t understart why it doesn’t return frame.

  Can anyone help with these problems ?

• ffmpeg - Overlay webm video (with alpha channel) over a static background image

  24 février 2023, par Aran

  I'm trying to overlay a webm video over an image. The video has opacity where the image should show through. All my attempts to do this via ffmpeg so far have shown the image in the first frame, then cut to the video only where the alpha part shows black (image behind is not visible).

  


  The resolutions of the overlay and background image are both the same (1920x1080).

  


  The closest command I've had was this however all transparency is lost and you just see the background image :

  


  ffmpeg -y \
  -i transparent_overlay_video.webm \
  -i background_image.png \
  -filter_complex "[0:v]format=argb,geq=r='r(X,Y)':a='1.0*alpha(X,Y)'[zork]; \
  [1:v][zork]overlay" \
  -vcodec libx264 outputvideo.mp4


  


  Solution

  


  ffmpeg -y \
  -c:v libvpx \
  -i transparent_overlay_video.webm \
  -i background_image.png \
  -filter_complex "[0:v]format=argb,geq=r='r(X,Y)':a='1.0*alpha(X,Y)'[zork]; \
  [1:v][zork]overlay" \
  -vcodec libx264 outputvideo.mp4


  


  Thanks to Баяр-Гончикжапов below for the solution