Re: [FFmpeg-devel] [PATCH v2 0/4] Add hevc alpha layer decoding basic support

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Jan 6, 2023, at 23:52, Zhao Zhili <quinkblack@foxmail.com> wrote:
> 
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> v2:
> 1. Check vps_max_layers and vps_max_layer_id inside hevc decoder
> 2. Add hevc_extract_layer bsf to do the job rather than modifing hevc_metadata,
> 3. Check vps_max_layers_minus1 and vps_max_layer_id inside bsf
> 4. Update vps_max_layers_minus1 and vps_max_layer_id when rewrite as base layer
> 5. vps_extension should be updated rather than drop entirely, add a TODO

Will push soon if there's no objections.

> 
> ---------------------------------------------
> 1. Don't drop nal->nuh_layer_id > 0 until decoder.
> 2. Make hevcdec able to decode a selected layer.
> 3. Add hevc_extract_layer bsf to extract a selected layer.
> 
> Partially fix #7965. There is a sample in ticket #7965 which can be used to test
> the patchset. Or use videotoolbox encoder to create a sample (FFmpeg needs to be
> patched first, "avutil/hwcontext_videotoolbox: BGRA should be full range"
> http://ffmpeg.org/pipermail/ffmpeg-devel/2023-January/305252.html), e.g.,
> 
> ./ffmpeg -i cctv.mp4 \
>    -i pig.mp4 \
>    -c:v hevc_videotoolbox \
>    -alpha_quality 0.75 \
>    -filter_complex '[1:v]scale=640x480[v1];[0:v][v1]alphamerge[v2]' \
>    -map [v2] -an -t 60 \
>    -pix_fmt bgra \
>    -b:v 4M \
>    -tag:v hvc1 \
>    alpha.mp4 -y
> 
> 
> Now it's able to use two decoders to decode the base layer and alpha
> layer, and then combine the results, e.g.,
> 
> ./ffmpeg -i alpha.mp4 \
> 	-strict -2  -nuh_layer_id 1 -i alpha.mp4 \
> 	-frames 60 \
> 	-filter_complex '[0:v][1:v]alphamerge[vout]' \
> 	-map '[vout]' -an test-%d.png
> 
> It only works with software decoder.
> 
> hevc_extract_layer can be used together with hardware decoder. The following
> example is how to extract the alpha layer and rewrite as base layer:
> 
> ./ffmpeg -i alpha.mp4 \
>   -an -c:v copy \
>   -bsf:v hevc_extract_layer=nuh_layer_id=1 \
>   test.mp4
> 
> Zhao Zhili (4):
>  avcodec/hevc_parse: keep nal->nuh_layer_id > 0
>  avcodec/cbs_h2645: keep nal->nuh_layer_id > 0
>  avcodec/hevcdec: add nuh_layer_id option
>  avcodec: add hevc_extract_layer bsf
> 
> configure                           |   1 +
> doc/bitstream_filters.texi          |  12 +++
> libavcodec/Makefile                 |   1 +
> libavcodec/bitstream_filters.c      |   1 +
> libavcodec/cbs_h2645.c              |   3 -
> libavcodec/hevc_extract_layer_bsf.c | 126 ++++++++++++++++++++++++++++
> libavcodec/hevc_parse.c             |   2 -
> libavcodec/hevcdec.c                |  56 ++++++++++++-
> libavcodec/version.h                |   2 +-
> 9 files changed, 197 insertions(+), 7 deletions(-)
> create mode 100644 libavcodec/hevc_extract_layer_bsf.c
> 
> -- 
> 2.25.1
> 
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