[FFmpeg-trac] #8468(ffmpeg:new): VP9 will not encode in yuva420p

[FFmpeg]

#8468: VP9 will not encode in yuva420p
--------------------------------+----------------------------------
             Reporter:  doard   |                     Type:  defect
               Status:  new     |                 Priority:  normal
            Component:  ffmpeg  |                  Version:  4.2
             Keywords:          |               Blocked By:
             Blocking:          |  Reproduced by developer:  0
Analyzed by developer:  0       |
--------------------------------+----------------------------------
 I need to convert prores yuva videos to VP9 webm and preserve the alpha
 channel. The encoder (libvpx-vp9) says it supports yuva420p but the output
 video is yuv420p.

 Show that my build supports yuva420p encoding
 {{{
 % ffmpeg.exe -help encoder=libvpx-vp9
 ffmpeg version n4.2.2 Copyright (c) 2000-2019 the FFmpeg developers
   built with gcc 9.2.0 (Rev2, Built by MSYS2 project)
   configuration: --arch=x86_64 --target-os=mingw32 --enable-runtime-
 cpudetect --enable-pthreads --enable-nonfree --disable-w32threads
 --disable-debug --disable-gpl --enable-version3 --disable-doc --enable-
 libopenh264 --enable-libvpx --enable-libmp3lame --enable-openssl --enable-
 iconv --enable-libxml2 --enable-libvorbis --enable-libaom --enable-libass
 --enable-gmp --enable-ffnvcodec --enable-libmfx --enable-nvdec --enable-
 cuvid --enable-dxva2 --enable-libsrt --enable-d3d11va --enable-shared
 --enable-static --enable-decklink --extra-cflags='-O3 -w -ftree-vectorize
 -DLIBXML_STATIC -DWINVER=0x0A00 -D_WIN32_WINNT=0x0A00
 -I../Blackmagic_DeckLink_SDK_10.11.4/Win/include' --extra-ldflags
 ='-static-libgcc -static-libstdc++
 -L../Blackmagic_DeckLink_SDK_10.11.4/Win/include'
 --prefix=../../../Build/ffmpeg_4.2.2/x64
   libavutil      56. 31.100 / 56. 31.100
   libavcodec     58. 54.100 / 58. 54.100
   libavformat    58. 29.100 / 58. 29.100
   libavdevice    58.  8.100 / 58.  8.100
   libavfilter     7. 57.100 /  7. 57.100
   libswscale      5.  5.100 /  5.  5.100
   libswresample   3.  5.100 /  3.  5.100
 Encoder libvpx-vp9 [libvpx VP9]:
     General capabilities: delay threads
     Threading capabilities: auto
     Supported pixel formats: yuv420p yuva420p yuv422p yuv440p yuv444p
 yuv420p10le yuv422p10le yuv440p10le yuv444p10le yuv420p12le yuv422p12le
 yuv440p12le yuv444p12le gbrp gbrp10le gbrp12le
 }}}

 Command to encode
 {{{
 % ffmpeg -i "D:\Videos\str_0010_introTransition_prores4444_v001.mov" -y
 -an -vcodec libvpx-vp9 -b:v 0 -tile-columns 6 -crf 18 -pix_fmt yuva420p
 "D:\Videos\str_0010_introTransition_test.webm"
 }}}

 Output from ffmpeg: Note that it says it's encoding with pixel format
 yuva420p
 {{{
 [libvpx-vp9 @ 000001be1f1f2900] v1.8.1-133-g802569640
 Output #0, webm, to 'D:\Videos\str_0010_introTransition_test.webm':
   Metadata:
     major_brand     : qt
     minor_version   : 512
     compatible_brands: qt
     uk.co.thefoundry.Application: Nuke
     uk.co.thefoundry.ApplicationVersion: 9.0v7
     uk.co.thefoundry.YCbCrMatrix: Rec 709
     uk.co.thefoundry.Colorspace: sRGB
     uk.co.thefoundry.Writer: mov64
     encoder         : Lavf58.29.100
     Stream #0:0(eng): Video: vp9 (libvpx-vp9), yuva420p, 12544x1792 [SAR
 1:1 DAR 7:1], q=-1--1, 24 fps, 1k tbn, 24 tbc (default)
     Metadata:
       handler_name    : VideoHandler
       encoder         : Lavc58.54.100 libvpx-vp9
     Side data:
       cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
 frame=   44 fps=1.4 q=0.0 size=       1kB time=00:00:00.79 bitrate=
 10.0kbits/s speed=0.0249x
 }}}

 Verify pixel format encoded in output video
 {{{
 % ffmpeg -i "D:\Videos\str_0010_introTransition_test.webm"
 }}}

 Output: Note that pixel format is now yuv420p, no alpha
 {{{
 ffmpeg version 4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
   built with gcc 9.1.1 (GCC) 20190807
   configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-
 fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-
 libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame
 --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
 --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr
 --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack
 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2
 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-
 libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa
 --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx
 --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-
 nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt
   libavutil      56. 31.100 / 56. 31.100
   libavcodec     58. 54.100 / 58. 54.100
   libavformat    58. 29.100 / 58. 29.100
   libavdevice    58.  8.100 / 58.  8.100
   libavfilter     7. 57.100 /  7. 57.100
   libswscale      5.  5.100 /  5.  5.100
   libswresample   3.  5.100 /  3.  5.100
   libpostproc    55.  5.100 / 55.  5.100
 Input #0, matroska,webm, from
 'D:\Videos\str_0010_introTransition_test.webm':
   Metadata:
     UK.CO.THEFOUNDRY.WRITER: mov64
     MAJOR_BRAND     : qt
     MINOR_VERSION   : 512
     COMPATIBLE_BRANDS: qt
     UK.CO.THEFOUNDRY.APPLICATION: Nuke
     UK.CO.THEFOUNDRY.APPLICATIONVERSION: 9.0v7
     UK.CO.THEFOUNDRY.YCBCRMATRIX: Rec 709
     UK.CO.THEFOUNDRY.COLORSPACE: sRGB
     ENCODER         : Lavf58.29.100
   Duration: N/A, start: 0.000000, bitrate: N/A
     Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv), 12544x1792, SAR
 1:1 DAR 7:1, 24 fps, 24 tbr, 1k tbn, 1k tbc (default)
     Metadata:
       alpha_mode      : 1
       HANDLER_NAME    : VideoHandler
       ENCODER         : Lavc58.54.100 libvpx-vp9
 At least one output file must be specified
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8468>
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