[FFmpeg-user] Green line with vaapi scaling

[André Hänsel]

When I scale with scale_vaapi, it results in a green line at the bottom of
the image, see attachment.

Command line:
ffmpeg -hwaccel vaapi -vaapi_device /dev/dri/renderD128
-hwaccel_output_format vaapi -i bbb.mp4 -vf
"scale_vaapi=w=240:h=135:format=yuv420p,hwdownload,format=yuv420p" -frames 1
out.png

It probably matters that I'm scaling to a height that is not divisible by 2
or 16. The input video here is Big Buck Bunny 1080p.

Extra question: Why do I need the second "format=yuv420p" after the
hwdownload filter? If I omit it, FFmpeg just gets stuck.

For completeness, the console output of above conversion:

# ffmpeg -hwaccel vaapi -vaapi_device /dev/dri/renderD128
-hwaccel_output_format vaapi -i bbb.mp4 -vf
"scale_vaapi=w=240:h=135:format=yuv420p,hwdownload,format=yuv420p" -frames 1
out.png
ffmpeg version 3.3.1-1~16.04.york0 Copyright (c) 2000-2017 the FFmpeg
developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
  configuration: --prefix=/usr --extra-version='1~16.04.york0'
--toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu
--incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping
--enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa
--enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca
--enable-libcdio --enable-libflite --enable-libfontconfig
--enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm
--enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt
--enable-libopus --enable-libpulse --enable-librubberband --enable-libshine
--enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh
--enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx
--enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid
--enable-libzmq --enable-libzvbi --enable-omx --enable-openal
--enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883
--enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264
--enable-shared
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libavresample   3.  5.  0 /  3.  5.  0
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
libva info: VA-API version 0.39.4
libva info: va_getDriverName() returns 0
libva info: Trying to open /usr/lib/x86_64-linux-gnu/dri/i965_drv_video.so
libva info: Found init function __vaDriverInit_0_39
libva info: va_openDriver() returns 0
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'bbb.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.16.100
  Duration: 00:00:09.25, start: 0.000000, bitrate: 11411 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv,
bt709), 1920x1080, 11408 kb/s, 24 fps, 24 tbr, 19200 tbn, 38400 tbc
(default)
    Metadata:
      rotate          : 0
      handler_name    : VideoHandler
    Side data:
      displaymatrix: rotation of -0.00 degrees
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> png (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'out.png':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.71.100
    Stream #0:0(und): Video: png, rgb24, 240x135, q=2-31, 200 kb/s, 24 fps,
24 tbn, 24 tbc (default)
    Metadata:
      encoder         : Lavc57.89.100 png
      handler_name    : VideoHandler
    Side data:
      displaymatrix: rotation of -0.00 degrees
frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
speed=0.883x
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing
overhead: unknown
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