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• lavc/rawdec : Use AV_PIX_FMT_PAL8 for 1-bit raw QuickTime video

  17 janvier 2016, par Mats Peterson

  lavc/rawdec : Use AV_PIX_FMT_PAL8 for 1-bit raw QuickTime video
  Match the use of AV_PIX_FMT_PAL8 for 1-bit QuickTime Animation in
  
  lavc/qtrle. To reiterate, 1-bit video is not necessary black & white in
  
  QuickTime, merely bi-level. The two colors can be any color. The palette,
  
  either included in the sample description, or the default Macintosh
  
  palette (black & white for 1-bit video) will be set in lavf/qtpalette.
  
  See the QuickTime File Format Specification for details.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/raw.c
  • [DH] libavcodec/rawdec.c

• lavf/qtpalette : Ignore greyscale bit in certain cases

  2 janvier 2016, par Mats Peterson

  lavf/qtpalette : Ignore greyscale bit in certain cases
  The QuickTime File Format Specification states the following :
  "Depth : A 16-bit integer that indicates the pixel depth of the
  
  compressed image. Values of 1, 2, 4, 8 ,16, 24, and 32 indicate the
  
  depth of color images. The value 32 should be used only if the image
  
  contains an alpha channel. Values of 34, 36, and 40 indicate 2-, 4-, and
  
  8-bit grayscale, respectively, for grayscale images."
  There is no mention of value 33, i.e. 1-bit video (0x01) with the
  
  greyscale bit (0x20) set. I therefore suggest that we ignore the
  
  greyscale bit when processing 1-bit video. Another reason to do this is
  
  that the first 1-bit sample file below will be displayed properly with
  
  blue colors in QuickTime in Windows or Mac *in spite of* the greyscale
  
  bit being set.
  Also, QuickTime in Windows or Mac ignores the greyscale bit if the
  
  video sample description contains a palette, regardless of bit depth.
  
  This is undocumented behaviour, but I think we should do the same, and
  
  it seems pretty logical after all, since one wouldn’t really bother
  
  putting a customized palette into a grayscale file anyway. See the
  
  second 8-bit sample file below, which has the greyscale bit set, and
  
  which contains a palette in the video sample description. In Windows or
  
  Mac, it will be displayed with the palette in the sample description, in
  
  spite of the greyscale bit being set.
  Sample file 1 (1-bit QuickTime Animation) :
  
  https://drive.google.com/open?id=0B3_pEBoLs0faTThSek1EeXQ0ZHM
  
  Earth Spin 1-bit qtrle orig.mov
  Sample file 2 (8-bit QuickTime Animation) :
  
  https://drive.google.com/open?id=0B3_pEBoLs0fad2s0V1YzUWo5aDA
  
  quiz-palette+gs.mov
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/qtpalette.c

• How to use FFmpeg filters setsar and setdar when generating animated gif ?

  1er janvier 2016, par Konstantin

  I would like to make an animated gif from a small section of an mp4 video file. Unfortunately the mp4 video file has bad aspect ratio. Instead of 4:3 (640x480) it is 3:2 (720x480). When I call "ffmpeg -i" on the video I can see :

   Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709), 720x480 [SAR 8:9 DAR 4:3], 1835 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 180k tbc (default)

  When I play it with VLC media player, it shows corrected aspect ratio, becasue I think it honours the DAR value (4:3), which is set in the mp4 video. However when I try to transcode to animated gif, that animated image file format doesn’t store such an information as DAR, because the pixels are always square shaped. So when I call my simple conversion script called movie2gif :

  #!/bin/sh
  
  
  
  video=$1
  
  max_colors=$2
  
  ss=$3
  
  t=$4
  
  out=$5
  
  palette="/tmp/palette.png"
  
  fps=18
  
  filt="fps=fps=$fps,setdar=4:3,scale=150:-1,lutyuv=y=gammaval(0.4),"
  
  
  
  
  
  ffmpeg -ss $ss -t $t -i "$video" -sws_flags lanczos -lavfi "$filt palettegen=max_colors=$max_colors:stats_mode=full" -vsync 0 -y "$palette"
  
  ffmpeg -ss $ss -i "$video" -i "$palette" -sws_flags lanczos -lavfi "$filt paletteuse=dither=bayer:bayer_scale=1" -vsync 0 -t $t -pix_fmt pal8 -gifflags +transdiff -y -f gif "$5"

  I always get a 150x100 pixel animated gif. I tried different values / expressions for setting both or one of the values of "setsar" and "setdar", in different order, placing them before the "scale" and after the "scale" filter, they have no effect on the resulting animated gif dimensions, it is always 150x100 pixels. How can I use these two filter properly to get a correct result, a 150x112 animated gif image ?