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• Stack AVFrame side by side (libav/ffmpeg)

  22 février 2018, par dronemastersaga

  So I am trying to combine two H264 livestreams of 1920x1080 resolution side-by-side to a livestream of 3840x1080 resolution.

  For this, I can decode streams to AVFrames in libav/FFmpeg that I would like to combine into a bigger frame. The Input AVFrames : Two 1920x1080 frames in NV12 format (description : planar YUV 4:2:0, 12bpp, 1 plane for Y and 1 plane for the UV components, which are interleaved (first byte U and the following byte V))

  The way I have figured out is with colorspace conversion (YUV to BGR) in libav, then to change it to OpenCV Mat, then to use hconcat in OpenCV to stack together, then colorspace conversion (BGR to YUV) in AVFormat.

  Below is the method currently being used :

  //Prior code is too long: Basically it decodes 2 streams to AVFrames frame1 and frame2 in a loop
  
  sws_scale(swsContext, (const uint8_t *const *) frame1->data, frame1->linesize, 0, 1080, (uint8_t *const *) frameBGR1->data, frameBGR1->linesize);
  
  sws_scale(swsContext, (const uint8_t *const *) frame2->data, frame2->linesize, 0, 1080, (uint8_t *const *) frameBGR2->data, frameBGR2->linesize);
  
  Mat matFrame1(1080, 1920, CV_8UC3, frameBGR1->data[0], (size_t) frameBGR1->linesize[0]);
  
  Mat matFrame2(1080, 1920, CV_8UC3, frameBGR2->data[0], (size_t) frameBGR2->linesize[0]);
  
  Mat fullFrame;
  
  hconcat(matFrame1, matFrame2, fullFrame);
  
  const int stride[] = { static_cast<int>(fullFrame.step[0]) };
  
  sws_scale(modifyContext, (const uint8_t * const *)&amp;fullFrame.data, stride, 0, fullFrame.rows, newFrame->data, newFrame->linesize);
  
  //From here, newFrame is sent to the encoder
  
  </int>

  The resulting image is satisfactory but it does lose quality in colorspace conversion. However this method is too slow to use (I’m at 15 fps and I need 30). Is there a way to stack AVFrames directly without colorspace conversion ? Or is there any better way to do this ? I searched a lot about this and I couldn’t find any solution to this. Please advise.

• FFMPEG, resize and pad a video by and odd number of pixels ?

  18 février 2018, par Jules

  I’m trying to resize and pad a video from 1917 x 1080 to 1920 x 1080.

  I’ve tried various syntax, which works but doesn’t change the size.

  ffmpeg -i input.mp4 -filter:v scale=1920:1080,pad=1920:1080 -c:a copy output.mp4

  However, I have go to this point by resize, joint audio and rotate. The initial size is 640 x 1136, I believe this is the source of the problem.

  ffmpeg -i input.mp4 -filter:v scale=900:1200 -c:a copy output.mp4
  
  
  
  ffmpeg \
  
  -i input.m4a \
  
  -i resize.mp4 -acodec copy -vcodec copy -shortest \
  
  output.mp4
  
  
  
  ffmpeg -i input.mp4" -vf "transpose=2" output/mp4

  So I’m wondering if I should do something different earlier

• ffmpeg scale/forcing fixed video resolution issue

  31 janvier 2018, par Massimo Vantaggio

  I try to be sure that the video comes out with a resolution of 1920 x1080,
  If not the encoding must force this resolution.
  I need this to create fine adaption set from a video input with standard resolution (HD).

  Im unable to get always this resolution, for example with a movie of
  1920 x 1040 i get 1993 x 1080

  , below my ffmpeg command line :

  ffmpeg -y -i $name -i logo1080.png -c:a aac -b:a 256k -ar 48000 -ac 2 -async 1 -c:v libx264 -x264opts keyint=$GOP:min-keyint=$GOP:no-scenecut -bf 0 -r $FPSC -b:v 2400k -maxrate 2400k -bufsize 1200k -profile:v main -t $FDUR -filter_complex "[0:v][1:v]overlay=main_w-overlay_w-10:10,scale=1920:1080" format1080.mp4

  I tried every possibility that the ffmpeg scale page tells, without understand how to fix it.
  I think i need some help,
  Thanks,
  Massimo