[FFmpeg-trac] #2158(swscale:open): Transparency gets lost on conversion from pal8 to yuva* (was: overlay filter does not work with pal8 transparency)

[FFmpeg]

#2158: Transparency gets lost on conversion from pal8 to yuva*
------------------------------------+-----------------------------------
             Reporter:  cehoyos     |                    Owner:
                 Type:  defect      |                   Status:  open
             Priority:  normal      |                Component:  swscale
              Version:  git-master  |               Resolution:
             Keywords:  alpha       |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+-----------------------------------
Changes (by cehoyos):

 * keywords:  overlay alpha => alpha
 * status:  new => open
 * component:  avfilter => swscale


Comment:

 I incorrectly assumed the overlay filter would accept pal8 as input, the
 real problem is that the transparency gets lost on conversion from pal8 to
 yuva*.
 {{{
 $ /ffmpeg -i pal8_alpha.png -pix_fmt yuva420p -vcodec ffv1 out.avi
 ffmpeg version N-49257-g77b740a Copyright (c) 2000-2013 the FFmpeg
 developers
   built on Jan 25 2013 02:57:07 with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl --disable-indev=jack
   libavutil      52. 15.103 / 52. 15.103
   libavcodec     54. 90.100 / 54. 90.100
   libavformat    54. 61.104 / 54. 61.104
   libavdevice    54.  3.102 / 54.  3.102
   libavfilter     3. 33.100 /  3. 33.100
   libswscale      2.  2.100 /  2.  2.100
   libswresample   0. 17.102 /  0. 17.102
   libpostproc    52.  2.100 / 52.  2.100
 Input #0, image2, from 'pal8_alpha.png':
   Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
     Stream #0:0: Video: png, pal8, 174x98, 25 tbr, 25 tbn, 25 tbc
 [ffv1 @ 0x2c23f40] Storing alpha plane, this will require a recent FFV1
 decoder to playback!
 Output #0, avi, to 'out.avi':
   Metadata:
     ISFT            : Lavf54.61.104
     Stream #0:0: Video: ffv1 (FFV1 / 0x31564646), yuva420p, 174x98,
 q=2-31, 200 kb/s, 25 tbn, 25 tbc
 Stream mapping:
   Stream #0:0 -> #0:0 (png -> ffv1)
 Press [q] to stop, [?] for help
 frame=    1 fps=0.0 q=0.0 Lsize=      11kB time=00:00:00.04
 bitrate=2195.6kbits/s
 video:5kB audio:0kB subtitle:0 global headers:0kB muxing overhead
 108.232170%
 }}}
 The output is opaque.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2158#comment:1>
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