[FFmpeg-trac] #7965(avcodec:open): Support for HEVC with Alpha

[FFmpeg]

#7965: Support for HEVC with Alpha
-------------------------------------+-----------------------------------
             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            |
-------------------------------------+-----------------------------------
Comment (by Igor):

 I noticed a recent commit that adds (some) support for packaging HEVC with
 alpha layer.
 https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/17e4746687abc53f0a042620a7af6dd6cea44b80

 However, I still cannot get a video that works. I am trying the following
 {{{
 ffmpeg -vcodec libvpx-vp9 -i input.webm -c:v libx265 -x265-params
 "alpha=1" output.mp4
 }}}

 Output
 {{{
 Input #0, matroska,webm, from 'input.webm':
   Metadata:
     encoder         : libwebm-0.3.0.0
     creation_time   : 2023-11-29T12:59:06.000000Z
   Duration: 00:00:03.00, start: 0.000000, bitrate: 4790 kb/s
   Stream #0:0(eng): Video: vp9 (libvpx-vp9) (Profile 0), yuva420p(tv),
 1200x1638, SAR 1:1 DAR 200:273, 30 fps, 30 tbr, 1k tbn (default)
     Metadata:
       alpha_mode      : 1
 [libvpx-vp9 @ 0x5591173d7000] v1.9.0

 Stream mapping:
   Stream #0:0 -> #0:0 (vp9 (libvpx-vp9) -> hevc (libx265))
 Press [q] to stop, [?] for help
 [libvpx-vp9 @ 0x5591173d7000] v1.9.0
 x265 [info]: HEVC encoder version 4.1+54-fa2770934
 x265 [info]: build info [Linux][GCC 10.2.1][64 bit] 8bit
 x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX
 FMA3 BMI2 AVX2
 x265 [info]: Main profile, Level-4 (Main tier)
 x265 [info]: Thread pool created using 12 threads
 x265 [info]: Slices                              : 1
 x265 [info]: frame threads / pool features       : 3 / wpp(26 rows)
 x265 [info]: Coding QT: max CU size, min CU size : 64 / 8
 x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra
 x265 [info]: ME / range / subpel / merge         : hex / 57 / 2 / 3
 x265 [info]: Keyframe min / max / scenecut / bias  : 25 / 250 / 40 / 5.00
 x265 [info]: Lookahead / bframes / badapt        : 20 / 4 / 2
 x265 [info]: b-pyramid / weightp / weightb       : 1 / 1 / 0
 x265 [info]: References / ref-limit  cu / depth  : 3 / off / on
 x265 [info]: AQ: mode / str / qg-size / cu-tree  : 2 / 1.0 / 32 / 1
 x265 [info]: Rate Control / qCompress            : CRF-28.0 / 0.60
 x265 [info]: tools: rd=3 psy-rd=2.00 early-skip rskip mode=1 signhide tmvp
 x265 [info]: tools: b-intra strong-intra-smoothing lslices=8 deblock sao
 alpha
 Output #0, mp4, to 'output.mp4':
   Metadata:
     encoder         : Lavf61.9.101
   Stream #0:0(eng): Video: hevc (hev1 / 0x31766568), yuva420p(tv,
 progressive), 1200x1638 [SAR 1:1 DAR 200:273], q=2-31, 30 fps, 15360 tbn
 (default)
     Metadata:
       encoder         : Lavc61.28.100 libx265
       alpha_mode      : 1
     Side data:
       cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
 }}}

 Funny that `ffmpeg` understands that the output should be in `yuva420p`
 but the resulting file isn't recognized by Safari or QuickTime on Mac, but
 plays on Windows without transparency (though like the input file).

 `ffprobe` does not recognize alpha layer (I guess when it says
 `Scalability type 2 not supported`)
 {{{
 [hevc @ 0x56075b908c40] Scalability type 2 not supported
 [hevc @ 0x56075b908c40] Ignoring unsupported VPS extension
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
   Metadata:
     major_brand     : isom
     minor_version   : 512
     compatible_brands: isomiso2mp41
     encoder         : Lavf61.9.101
   Duration: 00:00:03.00, start: 0.000000, bitrate: 854 kb/s
   Stream #0:0[0x1](eng): Video: hevc (Main) (hev1 / 0x31766568),
 yuv420p(tv, progressive), 1200x1638 [SAR 1:1 DAR 200:273], 842 kb/s, 30
 fps, 30 tbr, 15360 tbn (default)
     Metadata:
       handler_name    : VideoHandler
       vendor_id       : [0][0][0][0]
       encoder         : Lavc61.28.100 libx265
 [hevc @ 0x56075b925b40] Scalability type 2 not supported
 [hevc @ 0x56075b925b40] Ignoring unsupported VPS extension
 }}}
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/7965#comment:15>
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