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• ffmpeg poor YUV to RGB in sws_scale() (was : ffmpeg blocky chroma decoding)

  12 septembre 2017, par noiseshaper

  I’m using ffmpeg-3.2.4-win32, static and dev versions from zeranoe page, to decode some h264 mp4 videos I have created with x264 encoder. The videos have lots of static zones, 2d videogame type.

  When I decode their frames using either ffmpeg.exe or avcodec_decode_video2() API function, I get poor chroma resolution, blocky and quite visible in the static zones of the video (edit : avcodec_decode_video2() returns correct YUV, the problem is the YUV->RGB conversion, see my own answer below).

  With ffmpeg.exe I get poor chroma only if I output the frames to png, but if I output them to jpg, chroma seems much better (edit : this is due to poor YUV to RGB conversion of ffmpeg’s sws_scale()).

  Here is an example of the same frame obtained from a mp4 video created with a static image, the output frame is zoomed in to clearly see the effect.

  https://drive.google.com/file/d/0B5KI1D-N1kHpV3lGaERJRjNkcms/view

  1 : Original frame before compressing.

  2 : YUV 4:2:0 conversion before compressing

  3 : Video output from MPC HC + LAV decoder. This is YUV decoded output.

  4 : Video frames decoded with ffmpeg.exe to jpeg, quality is mostly ok, just some jpeg macroblocking is visible.

  5 : Video frames decoded with ffmpeg.exe to png, very blocky chroma. This is RGB output, using avcodec_decode_video2() and sws_scale() conversion to RGB produces the same blocky chroma.

  ---

  The command lines for decoding the frames to jpg and png are these :

  ffmpeg -i testcase.mp4 -vframes 5 -qscale:v 2 output%03d.jpg

  ffmpeg -i testcase.mp4 -vframes 5 output%03d.png

  You can download mp4 and bat files that showcase the effect here :

  https://drive.google.com/drive/folders/0B5KI1D-N1kHpcUdGd2IyM2pXMTg

  ---

  I have tried with ffmpeg 3.2, but same thing happens.

• avformat/oggparseogm : Fix undefined shift in ogm_packet()

  8 mars 2018, par Michael Niedermayer

  avformat/oggparseogm : Fix undefined shift in ogm_packet()
  Fixes : shift exponent 48 is too large for 32-bit type 'int'
  
  Fixes : Chromium bug 786793
  
  Reported-by : Matt Wolenetz <wolenetz@google.com>
  
  Reviewed-by : Matt Wolenetz <wolenetz@google.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/oggparseogm.c

• Converting images to video using javacv

  22 janvier 2014, par DanM

  Can you please help me with this code, it does not create anythind. I have followed the tutorial for implementing javacv in my app : https://code.google.com/p/javacv/

  My code :

  FFmpegFrameRecorder recorder = new FFmpegFrameRecorder(Environment
  
                  .getExternalStorageDirectory().getPath()
  
                  + "/MyApp/Media/test-ffmep.mp4", 640, 480);
  
          try {
  
              recorder.start();
  
          } catch (Exception e1) {
  
              // TODO Auto-generated catch block
  
              e1.printStackTrace();
  
          }
  
  
  
          for (int i = 1; i < 6; i++)
  
  
  
          {
  
              try {
  
                  recorder.record(opencv_highgui
  
                          .cvLoadImage("/sdcard/MyApp/Media/" + i + ".jpg"));
  
              } catch (Exception e) {
  
                  // TODO Auto-generated catch block
  
                  e.printStackTrace();
  
              }
  
          }
  
          try {
  
              recorder.stop();
  
          } catch (Exception e) {
  
              // TODO Auto-generated catch block
  
              e.printStackTrace();
  
          }