From: Zhao Zhili <zhiliz...@tencent.com>
What works:
1. Create a sample with macOS videotoolbox
ffmpeg -i base.mp4 -i alpha.mp4 \
-c:v hevc_videotoolbox -alpha_quality 0.5 -b:v 2M \
-filter_complex
'[0:v]scale,format=bgra[v0];[1:v]scale=640x480,format=gray[v1];[v0][v1]alphamerge[v2]'
\
-map '[v2]' -y hevc-alpha.ts
Then you can remux it to mp4 if you prefer.
2. Decoding test
a. Check alpha plane
./ffmpeg -i hevc-alpha.ts -an -vf extractplanes=planes=a -f nut - |ffplay -
b. Check Y plane
./ffmpeg -i hevc-alpha.ts -an -vf extractplanes=planes=y -f nut - |ffplay -
What doesn't work:
1. Encoding with videotoolbox and output as mp4 directly, due to missing PS.
Can be fixed by
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20241210191641.676-1-t...@rothenpieler.org/
2. vps_extension is over-engineering and decode_vps_ext() is far from complete.
A complete implementation might take a week, and I don't have enough spare time.
I would greatly appreciate it if someone could help implement it.
Branch on github:
https://github.com/quink-black/FFmpeg/tree/hevc-alpha-3
Zhao Zhili (5):
avcodec/hevc: Move ScalabilityMask to hevc header file
avcodec/hevc: Rewrite scalability_mask_flag parse in decode_vps_ext
avcodec/hevc/ps: Add basic HEVC_SCALABILITY_AUXILIARY support
avcodec/hevc/sei: Add support for alpha channel information
avcodec/hevc: Add alpha layer support
libavcodec/hevc/hevc.h | 7 +++
libavcodec/hevc/hevcdec.c | 75 ++++++++++++++++++++++++++++++-
libavcodec/hevc/hevcdec.h | 2 +
libavcodec/hevc/ps.c | 95 +++++++++++++++++++++++----------------
libavcodec/hevc/ps.h | 3 ++
libavcodec/hevc/refs.c | 10 ++++-
libavcodec/hevc/sei.c | 30 +++++++++++++
libavcodec/hevc/sei.h | 14 ++++++
8 files changed, 195 insertions(+), 41 deletions(-)
--
2.46.0
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