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• ffmpeg splitting RGB and Alpha channels using filter

  29 juin 2012, par Dow

  I'm trying to use ffmpeg to split an input file into two separate files :

  1. An MP4 with only R,G and B channels
  2. An MP4 with the "extracted" A channel (a so-called Key clip, see http://ffmpeg-users.933282.n4.nabble.com/quot-Extracting-quot-Alpha-Channel-td3700227.html)

  I've managed to do both, but now I want to combine them into one single command. Here's what I do :

  ffmpeg -r $FPS -y -i input.flv -vcodec libx264 -vpre ipod640 -acodec libfaac -s 256x256 -r $FPS -filter_complex INSERT_FILTER_HERE rgb.mp4 alpha.mp4

  where INSERT_FILTER_HERE is :

  format=rgba, split [rgb_in][alpha_in];
  
  [rgb_in] fifo, lutrgb=a=minval [rgb_out];
  
  [alpha_in] format=rgba, split [T1], fifo, lutrgb=r=maxval:g=maxval:b=maxval, [T2] overlay [out];
  
  [T1] fifo, lutrgb=r=minval:g=minval:b=minval [T2]

  In short, I split the file into two streams, for the first stream, I "remove" the alpha channel, for the second stream, I extract a grayscale representation of the alpha channel. When I put this through graph2dot, it works fine, with a nullsink as output.

  However, when I run it in ffmpeg with -filter_complex, I get :

  ffmpeg version N-41994-g782763e Copyright (c) 2000-2012 the FFmpeg developers
  
    built on Jun 28 2012 17:45:15 with gcc 4.6.3
  
    configuration: --enable-gpl --enable-nonfree --enable-pthreads --enable-filters --enable-libfaac --enable-libmp3lame --enable-libx264 --enable-libtheora --enable-libvpx --enable-postproc --enable-avfilter
  
    libavutil      51. 63.100 / 51. 63.100
  
    libavcodec     54. 29.101 / 54. 29.101
  
    libavformat    54. 11.100 / 54. 11.100
  
    libavdevice    54.  0.100 / 54.  0.100
  
    libavfilter     3.  0.100 /  3.  0.100
  
    libswscale      2.  1.100 /  2.  1.100
  
    libswresample   0. 15.100 /  0. 15.100
  
    libpostproc    52.  0.100 / 52.  0.100
  
  Input #0, flv, from 'input.flv':
  
    Metadata:
  
      audiodelay      : 0
  
      canSeekToEnd    : true
  
    Duration: 00:01:10.56, start: 0.000000, bitrate: 1964 kb/s
  
      Stream #0:0: Video: vp6a, yuva420p, 800x950, 1536 kb/s, 25 tbr, 1k tbn, 1k tbc
  
      Stream #0:1: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
  
  [graph 0 input from stream 0:0 @ 0x2e4c6e0] w:800 h:950 pixfmt:yuva420p tb:1/30 fr:30/1 sar:0/1 sws_param:flags=2
  
  Output pad "default" for the filter "Parsed_lutrgb_3" of type "lutrgb" not connected to any destination

  Any ideas on how I make ffmpeg recognize that it has to write [rgb_out] to rgb.mp4 and [out] to alpha.mp3 ?

  Thanks in advance !

• Revision 679e4abdd5 : Initial version of alpha channel support This is a mostly-working implementatio

  16 mai 2013, par John Koleszar

  Changed Paths :
   Modify /configure

  
   Modify /vp9/common/vp9_alloccommon.c

  
   Modify /vp9/common/vp9_blockd.h

  
   Modify /vp9/common/vp9_extend.c

  
   Modify /vp9/common/vp9_mbpitch.c

  
   Modify /vp9/common/vp9_onyxc_int.h

  
   Modify /vp9/common/vp9_postproc.c

  
   Modify /vp9/common/vp9_reconinter.c

  
   Modify /vp9/common/vp9_reconinter.h

  
   Modify /vp9/encoder/vp9_encodeframe.c

  
   Modify /vp9/encoder/vp9_encodemb.c

  
   Modify /vp9/encoder/vp9_lookahead.c

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/encoder/vp9_onyx_int.h

  
   Modify /vp9/encoder/vp9_quantize.c

  
   Modify /vp9/encoder/vp9_rdopt.c

  
   Modify /vp9/encoder/vp9_temporal_filter.c

  
   Modify /vp9/vp9_iface_common.h

  
   Modify /vpx_scale/generic/yv12config.c

  
  
  Initial version of alpha channel support

  This is a mostly-working implementation of an extra channel in the
  bitstream. Configure with —enable-alpha to test. Notable TODOs :

  - Add extra channel to all mismatch tests, PSNR, SSIM, etc
  - Configurable subsampling
  - Variable number of planes (currently always uses all 4)
  - Loop filtering
  - Per-plane lossless quantizer
  - ARNR support

  This implementation just uses the same contents as the Y channel
  for the A channel, due to lack of content and general pain in
  playing back 4 channel content. A later patch will use the actual
  alpha channel passed in from outside the codec.

  Change-Id : Ibf81f023b1c570bd84b3064e9b4b8ae52e087592

• avformat/electronicarts : add option to return alpha channel in the main video stream...

  13 novembre 2022, par Marton Balint

  avformat/electronicarts : add option to return alpha channel in the main video stream in VP6A codec
  VP6 alpha in EA format is a second VP6 encoded video stream where only the Y
  
  component is used and is interpreted as the alpha channel of the first VP6
  
  stream. The alpha VP6 stream is muxed separately from the main VP6 stream, has
  
  its own stream headers and packet headers. In theory the two streams might not
  
  even have the same resolution (although most likely that is not something that
  
  is seen or supported in the wild), but the format is capable of doing it.
  Merged VP6 alpha (also known as the VP6A codec) means that a packet of the
  
  video stream contains the corresponding packet of both VP6 substreams like
  
  this :
  OffsetOfAlpha, DataPacket, AlphaDataPacket
  So data and alpha data of a frame is merged to a single packet, this is how VP6
  
  video with alpha is muxed in FLV and SWF.
  The first approach is more like how the demuxer sees data in the EA format,
  
  unfortunately it is different to what the FLV or SWF format expects, so -
  
  having no better place for it in the framework - I decided to do an optional
  
  format conversion in the EA demuxer.
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] doc/demuxers.texi
  • [DH] libavformat/electronicarts.c
  • [DH] libavformat/version.h