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• Scenecut detection and consistent GOP size - adaptive streaming

  24 mars 2014, par Tarun

  Sample Command :

  -map 0:0 -f mp4 -vcodec libx264 -preset slow -profile:v main -vf scale="640:trunc(ow/a/2)*2" -vb 700k -minrate 650k -maxrate 750k -bufsize 10000k -an -g 48 -x264opts keyint=48:min-keyint=10:scenecut=40 -flags +cgop -sc_threshold 40 -pix_fmt yuv420p -threads 0 -y

  There is as such no error in encoding, But I wanted to understand following points-

  1) the above command will ensure that range of GOP size is 10,48, and if any scene change value (frame1 to fame2) is >40%, then a keyframe is introduced there ?

  2) So that means in a 3 hours of source video, there is no guarantee that GOP size will remain same

  3) No consider, I am creating 7 MP4 files each with different bitrate and resolution. (These Mp4s will be encoded to smooth in later stage). Hence i am targeting adaptive streaming. But when I did that, I found that if GOP sizes were not consistent across each bitrates. What I mean by this is, for ex : if in Bitrate1 - GOP size is like 10, 20, 48 and so on, in other bitrates it wasnt in the same sequence. I hope my question makes sense.

  So is there a way to ensure that GOP size may vary across one single output. But it should be consistent across each bitrate provided that the source is same ?

  Also for adaptive streaming Is scenecut detection advisable ?

• OpenCV Java binds VideoCapture from file failing silently

  8 décembre 2014, par muz0

  I’m using OpenCV 2.4.8 with the supplied Windows 64bit Java jar. I’ve been making full use of OpenCV in my current environment up until this point.

  I’m unable to open video files using the
  VideoCapture class however webcam feeds work just fine.

  The below works as expected with video.isOpened returning true

      VideoCapture video = new VideoCapture();
  
      boolean result = video.open(0);

  The below fails with video.isOpened returning false

      VideoCapture video = new VideoCapture();
  
      boolean result = video.open("res/hand-test-1.mp4");

  Neither file formats seems to make a difference (These are converted, not just renamed in hope)

      video.open("res/hand-test-1.mp4");
  
      video.open("res/hand-test-1.avi");
  
      video.open("res/hand-test-1.wmv");

  Location seems to matter not either.

      video.open("C:/hand-test-1.mp4");
  
      video.open("C:\\hand-test-1.mp4");
  
      video.open("hand-test-1.mp4");

  Neither does garbage, no exception kicked up from OpenCV through Java either, seems to fail silently.

      video.open("ashdkfhkajsjdfkhaksdf");

  PATH contains the ffmpeg directory supplied with the opencv installation,

      C:\dev\opencv\sources\3rdparty\ffmpeg

  Right now I’ve run out of ideas, it seems like whatever I throw to the native via video.open(String) will return false.

  Any help would be much appreciated

• How to transcode to another video parameters ? [on hold]

  23 mai 2014, par user3668381

  Google, man pages and any docs I found didn t shown anything relevant so...

  I want to be able to concatene video with ffmpeg, this part is simple, but fail (freeze or massive frame dropping) if the videos don t have the same properties.

  But for now, I didn t found anything else but trying to set a lot of options, expecting to get the good properties... But when they aren t rounded down (or up), you just can t set them (tbr, tbn...).

  So my question is, is there any hidden option in ffmpeg to take the properties of another video (so -copy won t work) as the properties of the transcode.

  Illustration :

  This is the video from which I wan t to copy the parameters :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'cdr.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      creation_time   : 2013-07-04 11:04:27
  
      encoder         : Lavf54.11.100
  
    Duration: 00:06:26.96, start: 0.000000, bitrate: 804 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 854x480 [SAR 1280:1281 DAR 16:9], 753 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc (default)
  
      Metadata:
  
        creation_time   : 2013-07-04 11:04:27
  
        handler_name    : VideoHandler
  
      Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 44 kb/s (default)
  
      Metadata:
  
        creation_time   : 2013-07-04 11:04:27
  
        handler_name    : SoundHandler
  
  At least one output file must be specified

  For now, my command is ffmpeg -i video.mp4 -c:v h264 -c:a libfdk_aac -aspect 16:9 -b:v 753k -b:a 44k output.mp4

  But it turn out that output.mp4 reveal :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf55.21.100
  
    Duration: 00:00:07.11, start: 0.046440, bitrate: 685 kb/s
  
      Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 854x480 [SAR 1280:1281 DAR 16:9], 637 kb/s, 15 fps, 15 tbr, 15360 tbn, 30 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 45 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler
  
  At least one output file must be specified

  As we can see, audio bitrate is rounded, tbn is off the chart, general bitrate isn t the same and on and on and on...

  Is there any better way but to add options again and again and hope that nothing will be rounded ? Something like ffmpeg -i video.mp4 -use_properties_of model.mp4 output.mp4 ?