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• Frame Accurate Seeking in WebM

  11 janvier 2016, par SapphireSun

  I’m trying to do a somewhat tricky thing with WebM. I am trying to encode a stack of 256 biological images as a WebM. The time dimension of motion is very similar to the space dimension of the image stack so the compression ratios are insanely good. However, I am having trouble decoding the movie frames. I know that WebM uses an IPB predictive coding scheme, but I was reading several blog posts and discussion groups from WHATWG from 2011, and they said that frame accurate seeking was working in Chrome at that time.

  When I do video.currentTime = 0, I correctly get this :

  

  However, if I do video.currentTime = 0.34 (for example) I get something that looks like this :

  

  It looks like I’m getting a random poorly predicted frame. Am I just encoding the video wrong ? When I play it normally it looks fine.

  I encoded the video using 256 pngs using ffmpeg compiled with libvpx using the VP8 codec.

  ffmpeg -y -framerate 60 -start_number 0 -pattern_type glob -i '*.png' -qmin 10 -qmax 42 out.webm

  References to the WHATWG and some other info from 2011 :

  WHATWG discusses frame accuracy :

  https://lists.w3.org/Archives/Public/public-whatwg-archive/2011Jan/0372.html

  BBC Tech Director talking about frame accuracy :

  http://www.bbc.co.uk/blogs/bbcinternet/2011/02/frame_accurate_video_in_html5.html

• Combine 2 .FLV videos

  4 décembre 2015, par Rune

  For the last 4 hours I’ve been trying to combine 2 .flv files into one using ffmpeg (or well, just C# in general).

  Here’s what I got so far :
  I’ve converted both the videos to .mp4 videos :

  "-i " + videoFileLocation + " -c copy -copyts " + newConvertedFileLocation

  I have then combined the two .mp4 files into a single one using :
  (txtPath is the text file with the two mp4 file locations)

  "-f concat -i " + txtPath + " -c copy " + saveLocation

  This ends up with an mp4 file which contains the combination of both the videos BUT with the following fault :

  The length of the first video is 0:05

  The length of the second video is 6:11

  However the length of the combined video is for some reason 07:51 - thus the video runs at a slower pace than it should.

  Furthermore the audio is async with the video.

  What am I doing wrong here ?

  I haven’t used ffmpeg before and I just wanna get this working.

  Any help is greatly appreciated !

  As requested here is the output from running ’ffmpeg -i input1.flv -i input2.flv’ :

  ffmpeg version 2.7 Copyright (c) 2000-2015 the FFmpeg developers   built with gcc 4.9.2 (GCC)...
  
  
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'filepath\input1.flv':   Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      creation_time   : 1970-01-01 00:00:00
  
      encoder         : Lavf53.24.2   Duration: 00:00:05.31, start: 0.000000, bitrate: 1589 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], 1205 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.1, fltp, 384 kb/s (default)
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
        handler_name    : SoundHandler Input #1, flv, from 'filepath\input2.flv':   Metadata:
  
      audiosize       : 4476626
  
      canSeekToEnd    : true
  
      datasize        : 23876671
  
      videosize       : 19004263
  
      hasAudio        : true
  
      hasCuePoints    : false
  
      hasKeyframes    : true
  
      hasMetadata     : true
  
      hasVideo        : true
  
      lasttimestamp   : 372
  
      metadatacreator : flvtool++ (Facebook, Motion project, dweatherford)
  
      totalframes     : 9298
  
      encoder         : Lavf56.36.100   Duration: 00:06:11.92, start: 0.080000, bitrate: 513 kb/s
  
      Stream #1:0: Video: h264 (High), yuv420p, 646x364 [SAR 1:1 DAR 323:182], 400 kb/s, 25 fps, 25 tbr, 1k tbn, 50 tbc
  
      Stream #1:1: Audio: aac (LC), 44100 Hz, stereo, fltp, 96 kb/s At least one output file must be specified

• Extracting video frame image with libavformat and libswscale gives flipped image

  21 novembre 2015, par ivan.ukr

  I am using following code to extract image frames outputted by avcodec_decode_video2() into BMP file :

  // Convert the image from its native format to RGB
  
  int height = sws_scale(state.sws_ctx, 
  
               (uint8_t const * const *)state.frame->data,
  
               state.frame->linesize, 
  
               0, 
  
               state.video_codec_ctx->height,
  
               state.picture.data, 
  
               state.picture.linesize);
  
  
  
  // ..... here BMP header initialization goes ...
  
  
  
  // Extract pixels
  
  {
  
      int y = 0;
  
      size_t frame_line_size = state.picture.linesize[0];
  
      uint8_t* bmp_data = &bmp->data[0];
  
      uint8_t* picture_data = state.picture.data[0];
  
      while(y < height)
  
      {
  
          memcpy(bmp_data, picture_data, image_line_size);
  
          bmp_data += image_line_size_with_padding;
  
          picture_data += frame_line_size;
  
          ++y;
  
      }
  
  }

  But it results flipped image :

  

  Can anyone please help me to understand, what I am doing wrong here ?

  Video stream information :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'testdata/video3.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      creation_time   : 1970-01-01 00:00:00
  
      title           : video3.mp4
  
      encoder         : Lavf52.78.3
  
    Duration: 00:00:07.93, start: 0.000000, bitrate: 1467 kb/s
  
      Stream #0.0(und): Video: h264 (High), yuv420p, 640x320 [PAR 1:1 DAR 2:1], 1331 kb/s, 29.73 fps, 29.73 tbr, 29734 tbn, 59.47 tbc
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
      Stream #0.1(und): Audio: aac, 48000 Hz, stereo, fltp, 127 kb/s
  
      Metadata:
  
        creation_time   : 1970-01-01 00:00:00
  
  Video file 'testdata/video3.mp4' has 236 frames.

  I have alternate code that uses libopencv, and it gives correct image from the same video file, but I need to reach the correct effect using directly ffmpeg libs.