[FFmpeg-trac] #11126(undetermined:new): Using filter setpts=PTS-STARTPTS in 2 pass vp9 webm causes final video bitrate to be small

[FFmpeg]

#11126: Using filter setpts=PTS-STARTPTS in 2 pass vp9 webm causes final video
bitrate to be small
-------------------------------------+-------------------------------------
             Reporter:  Saul Baker   |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:

 Converting an mp4 to vp9 webm displays a marked reduction in quality and
 small final video bitrate when the filter "setpts=PTS-STARTPTS" is applied
 during a 2 pass encode, 1 pass encodes do not display the same difference,
 nor does an arbitrary old version.

 How to reproduce:
 {{{

 ffmpeg -y -i "source.mp4" -filter_complex "setpts=PTS-STARTPTS"  -pass 1
 -passlogfile pass.log  -c:v libvpx-vp9 -c:a libopus  -pix_fmt yuv420p
 -quality good   -b:v 3271553 -an -sn -f null nul
 ffmpeg -y -i "source.mp4" -filter_complex "setpts=PTS-STARTPTS"  -pass 2
 -passlogfile pass.log  -c:v libvpx-vp9 -c:a libopus  -pix_fmt yuv420p
 -quality good   -b:v 3271553 -ac 1 -ar 48k -b:a 65536 -sn
 dest_2pass_setpts.webm

 ffmpeg -y -i "source.mp4" -filter_complex "null"  -pass 1 -passlogfile
 pass.log  -c:v libvpx-vp9 -c:a libopus  -pix_fmt yuv420p  -quality good
 -b:v 3271553 -an -sn -f null nul
 ffmpeg -y -i "source.mp4" -filter_complex "null"  -pass 2 -passlogfile
 pass.log  -c:v libvpx-vp9 -c:a libopus  -pix_fmt yuv420p  -quality good
 -b:v 3271553 -ac 1 -ar 48k -b:a 65536 -sn dest_2pass_nofilter.webm

 ffmpeg -y -i "source.mp4" -filter_complex "setpts=PTS-STARTPTS" -c:v
 libvpx-vp9 -c:a libopus  -pix_fmt yuv420p  -quality good   -b:v 3271553
 -ac 1 -ar 48k -b:a 65536 -sn dest_1pass_setpts.webm
 }}}

 ffprobe output for 2024-08-01-git-bcf08c1171
 {{{

 >> ffprobe dest_2pass_setpts.webm
 Duration: 00:00:41.73, start: -0.007000, bitrate: 68 kb/s

 >> ffprobe dest_2pass_nofilter.webm
 Duration: 00:00:41.73, start: -0.007000, bitrate: 3268 kb/s

 >> ffprobe dest_1pass_setpts.webm
 Duration: N/A, start: -0.007000, bitrate: N/A

 }}}

 ffprobe output for 2023-01-30-git-2d202985b7
 {{{

 >> ffprobe dest_2pass_setpts.webm
 Duration: 00:00:41.73, start: -0.007000, bitrate: 3268 kb/s

 >> ffprobe dest_2pass_nofilter.webm
 Duration: 00:00:41.73, start: -0.007000, bitrate: 3268 kb/s

 >> ffprobe dest_1pass_setpts.webm
 Duration: 00:00:41.73, start: -0.007000, bitrate: 2614 kb/s
 }}}




 {{{
 ffmpeg version 2024-08-01-git-bcf08c1171-essentials_build-www.gyan.dev
 Copyright (c) 2000-2024 the FFmpeg developers
   built with gcc 13.2.0 (Rev5, Built by MSYS2 project)
   configuration: --enable-gpl --enable-version3 --enable-static --disable-
 w32threads --disable-autodetect --enable-fontconfig --enable-iconv
 --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma
 --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable-
 avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265
 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx
 --enable-mediafoundation --enable-libass --enable-libfreetype --enable-
 libfribidi --enable-libharfbuzz --enable-libvidstab --enable-libvmaf
 --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-
 dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl
 --enable-nvdec --enable-nvenc --enable-vaapi --enable-libgme --enable-
 libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-
 libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-
 amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-
 librubberband
   libavutil      59. 31.100 / 59. 31.100
   libavcodec     61. 11.100 / 61. 11.100
   libavformat    61.  5.101 / 61.  5.101
   libavdevice    61.  2.100 / 61.  2.100
   libavfilter    10.  2.102 / 10.  2.102
   libswscale      8.  2.100 /  8.  2.100
   libswresample   5.  2.100 /  5.  2.100
   libpostproc    58.  2.100 / 58.  2.100
 }}}



 Patches should be submitted to the ffmpeg-devel mailing list and not this
 bug tracker.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11126>
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