[FFmpeg-trac] #4746(avcodec:new): prores alpha blending results in opaque rectangle

[FFmpeg]

#4746: prores alpha blending results in opaque rectangle
-------------------------------------+-------------------------------------
             Reporter:               |                    Owner:
  projectsymphony                    |                   Status:  new
                 Type:  defect       |                Component:  avcodec
             Priority:  normal       |               Resolution:
              Version:  git-master   |               Blocked By:
             Keywords:               |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by projectsymphony):

 yes I agree with gjdfgh, and what about conversion using ffmpeg?
 It's a well known behaviour that when alpha is converted to an opaque
 format it is blended with black by default


 btw, using the provided option with ffmpeg results in an infinite
 conversion

 {{{
 ffmpeg -i proresalphablock.mov  -vf
 'scale[in],color=black:1920x1080[back],[back][in]overlay' -pix_fmt yuv420p
 output.mov
 ffmpeg version N-73640-gae4c9dd Copyright (c) 2000-2015 the FFmpeg
 developers
   built with Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM
 3.5svn)
   configuration: --cc=clang --enable-debug --disable-optimizations
 --disable-yasm --disable-asm --enable-libfdk-aac --enable-version3
 --enable-nonfree --enable-gpl --disable-doc --enable-libmp3lame --enable-
 openssl --enable-libfreetype --enable-avresample --enable-libopenjpeg
 --enable-libx264
   libavutil      54. 28.100 / 54. 28.100
   libavcodec     56. 47.100 / 56. 47.100
   libavformat    56. 40.100 / 56. 40.100
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 21.100 /  5. 21.100
   libavresample   2.  1.  0 /  2.  1.  0
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  2.100 /  1.  2.100
   libpostproc    53.  3.100 / 53.  3.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'proresalphablock.mov':
   Metadata:
     major_brand     : qt
     minor_version   : 512
     compatible_brands: qt
     creation_time   : 2015-07-09 05:29:21
     encoder         : Lavf56.21.0
   Duration: 00:00:09.43, start: 0.031833, bitrate: 13066 kb/s
     Stream #0:0(eng): Video: prores (ap4h / 0x68347061), yuva444p10le,
 1920x1080, 13066 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 24k tbc (default)
     Metadata:
       creation_time   : 2015-07-09 05:29:21
       handler_name    : DataHandler
       encoder         : Apple ProRes 4444
 [libx264 @ 0x7fe10c03ce00] using SAR=1/1
 [libx264 @ 0x7fe10c03ce00] using cpu capabilities: MMX2 SSE2Fast SSSE3
 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
 [libx264 @ 0x7fe10c03ce00] profile High, level 4.0
 [libx264 @ 0x7fe10c03ce00] 264 - core 148 r2538+33M bff0ecd - H.264/MPEG-4
 AVC codec - Copyleft 2003-2015 - http://www.videolan.org/x264.html -
 options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7
 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1
 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12
 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0
 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1
 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25
 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0
 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
 Output #0, mov, to 'output.mov':
   Metadata:
     major_brand     : qt
     minor_version   : 512
     compatible_brands: qt
     encoder         : Lavf56.40.100
     Stream #0:0(eng): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p,
 1920x1080 [SAR 1:1 DAR 16:9], q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)
     Metadata:
       creation_time   : 2015-07-09 05:29:21
       handler_name    : DataHandler
       encoder         : Lavc56.47.100 libx264
 Stream mapping:
   Stream #0:0 -> #0:0 (prores (native) -> h264 (libx264))
 Press [q] to stop, [?] for help
 [..]
 frame=34281 fps= 48 q=28.0 size=    2458kB time=00:22:48.92 bitrate=
 14.7kbits/
 }}}

 I had to stop it manually, but this is probably a separate bug.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/4746#comment:9>
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