Newest 'ffmpeg' Questions - Stack Overflow

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• How to quantify and compare video quality

  24 mars 2015, par user940154

  I have a set of uncompressed videos in YUV format.

  I have obtained several derived copies in various formats and resolutions from these yuv files using FFmpeg transcoding. (YUVs ----> X Derived Copies)

  What I have also done is, transcode the yuv's into same resolution AVIs, and now obtained the same set of derived (transcoded) videos treating the AVIs as master. (AVIs ----> X Derived Copies)

  Now I wish to compare the quality of transcoded videos, when derived from AVIs to those derived from YUVs.

  Is there any way for me to do this using FFmpeg. How? If not, can you please suggest some good open source software to do this.

  Thanks

• FFMPEG thumbnail image gives black image

  24 mars 2015, par user3772344

  I am trying to get the thumbnail image of video using ffmpeg. but for some of the video it shows the black image. I have done the following code.

   KxMovieDecoder * decoder = [[KxMovieDecoder alloc] init];
  [decoder openFile:videoURL error:nil];
  gHistory = [[NSUserDefaults standardUserDefaults]objectForKey:[decoder.path lastPathComponent]];;
  
  NSArray *ar =  [decoder decodeFrames:1.0f];
  KxMovieFrame *frame;
  
  for (KxMovieFrame *frames in ar)
  {
      if (frames.type == KxMovieFrameTypeVideo) {
          frame =  ar.lastObject;
          break;
      }
  }
     KxVideoFrameRGB *rgbFrame = (KxVideoFrameRGB *)frame;
  UIImage *imageKX = [rgbFrame asImage];
  

  I don't know whats the wrong in this method

• My MKV to MP4 converted video doesn't play in flex

  24 mars 2015, par ketan

  I am stuck on one issue from last 1 day. I am using Adobe flex video display to play video for my site.

  There is some converted video from MKV to MP4 using ffmpeg.

  ffmpeg -i Test.mkv -vcodec copy -acodec copy Test.mp4
  

  Now, i am trying to play that video from local it's working fine. But when i upload that video on server and trying to play video. Then it will not work with flex VideoDisplay same will work in browser and HTML videoplayer and also works with JWPlayer.

  Other mp4 video which are not converted works very fine. Only converted Videos are not working in only flex VideoDisplay.

  I am Just playing using.

  And give path to videoDisplay like:

  videoDisp.source = Video_path;
  

  My video file Video and Audio codec is as shown in below image:

  

  Any help will be appreciate,
  Thanks.

• How to change libx264 profile when using ffmpeg backend of OpenCV

  24 mars 2015, par dvhamme

  I am using OpenCV 3.0.0 beta to write a video with VideoWriter vw("out.avi",VideoWriter::fourcc('h','2','6','4'),24,frame.size());

  This calls on the ffmpeg backend (avcodec version 56.26.100), which calls libx264 (build 142). However, apparently it is not possible to specify a libx264 profile from OpenCV, and the default bitrate is too low for my application.

  Where can I change the default behaviour of ffmpeg or possibly libx264 to get higher quality video written from OpenCV?

• Export frames/images from compressed video

  24 mars 2015, par Jan Viehweger

  I have a compressed movie (mp4) and I want to extract every single frame / image from it. I know that each individual frame of the video only contains the changed pixels regarding to the last keyframe, because of the video compression. But that is exactly what I want. I just want to see those differences. I want to visualy see how the compressor works.

  Is there some tool like imagemagick out there what can things like that?