#7965: Support for HEVC with Alpha
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Reporter: leemartin | Owner: (none)
Type: enhancement | Status: open
Priority: wish | Component: avcodec
Version: git-master | Resolution:
Keywords: hevc | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by logiclrd):
> As I understand x265 does not support alpha
It does now. As of version 4.0, which dropped a month or two back, there
is a `--alpha` command-line option. With this option, the input is assumed
to be a `yuva420p` raw stream. As of writing this, to get this latest
version you must build `x265` from source. At least on my OS, the central
package manager doesn't yet have version 4.0.
I have found the following sequence which //seems// to produce an MP4 file
with HEVC with alpha content, but I am not on a Mac and have found no way
to test it because the decoding support described by this ticket is not
yet implemented. :-)
{{{
x265 --input-res 606x692 --fps 30000/1001 --alpha --crf 20 Zap.yuva420p
Zap.hevc
mkvmerge Zap.hevc -o Zap.mkv
ffmpeg -itsscale 0.3336666666 -i Zap.mkv -c copy -vtag hvc1 Zap.mp4 -y
}}}
The `-itsscale` option is to fix an issue with the framerate. I couldn't
find a way to get `mkvmerge` to produce the right output (there may be a
way). By default, it seems to emit HEVC frames timestamped to 10fps. This
scale factor converts from 10fps to 30000/1001 fps.
Hopefully this information is helpful to someone.
There is a tool called Zond 265 which does some fascinating inspection of
internal H.265 encoding details. It does not support alpha channels yet,
and I was told that the reason is that FFMPEG doesn't decode HEVC with
Alpha yet.
I also found this related issue in Trac: #10901
(Does Trac have a mechanism for relationships between tickets?? A quick
web search suggests that the answer is //Yes//, but only if you use an
unmaintained plugin called `TracTicketReferencePlugin`...)
--
Ticket URL: <https://trac.ffmpeg.org/ticket/7965#comment:14>
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