[FFmpeg-trac] #6605(avfilter:new): Drawing subtitles on transparent video creates empty output

FFmpeg trac at avcodec.org
Mon Aug 21 19:40:26 EEST 2017


#6605: Drawing subtitles on transparent video creates empty output
-----------------------------------+--------------------------------------
             Reporter:  slhck      |                     Type:  defect
               Status:  new        |                 Priority:  normal
            Component:  avfilter   |                  Version:  git-master
             Keywords:  subtitles  |               Blocked By:
             Blocking:             |  Reproduced by developer:  0
Analyzed by developer:  0          |
-----------------------------------+--------------------------------------
 Trying to render subtitles on a transparent video background produces an
 empty, transparent PNG with no subtitles:

 {{{
 $ cat subs.srt
 1
 00:00:00,000 --> 00:00:02,000
 <i>Test</i>
 $ ffmpeg -f lavfi -i
 "color=color=white at 0.0:size=100x100,format=rgba,subtitles=subs.srt"
 -frames:v 1 out.png
 ffmpeg version N-87010-g3c99523-tessus Copyright (c) 2000-2017 the FFmpeg
 developers
   built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
   configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --extra-
 version=tessus --enable-avisynth --enable-fontconfig --enable-gpl
 --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm
 --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb
 --enable-libopencore-amrwb --enable-libopus --enable-libsnappy --enable-
 libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-
 libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack
 --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid
 --enable-libzmq --enable-libzvbi --enable-version3 --disable-ffplay
 --disable-indev=qtkit
   libavutil      55. 74.100 / 55. 74.100
   libavcodec     57.102.100 / 57.102.100
   libavformat    57. 76.100 / 57. 76.100
   libavdevice    57.  7.100 / 57.  7.100
   libavfilter     6. 99.100 /  6. 99.100
   libswscale      4.  7.102 /  4.  7.102
   libswresample   2.  8.100 /  2.  8.100
   libpostproc    54.  6.100 / 54.  6.100
 [Parsed_subtitles_2 @ 0x7fd134d00740] Shaper: FriBidi 0.19.2 (SIMPLE)
 [Parsed_subtitles_2 @ 0x7fd134d00740] Using font provider coretext
 [Parsed_subtitles_2 @ 0x7fd134d00740] fontselect: (Arial, 400, 0) ->
 /Library/Fonts/Arial.ttf, -1, ArialMT
 [Parsed_subtitles_2 @ 0x7fd134d00740] fontselect: (Arial, 400, 100) ->
 /Library/Fonts/Arial Italic.ttf, -1, Arial-ItalicMT
 Input #0, lavfi, from
 'color=color=white at 0.0:size=100x100,format=rgba,subtitles=subs.srt':
   Duration: N/A, start: 0.000000, bitrate: N/A
     Stream #0:0: Video: rawvideo (RGBA / 0x41424752), rgba, 100x100 [SAR
 1:1 DAR 1:1], 25 tbr, 25 tbn, 25 tbc
 File 'out.png' already exists. Overwrite ? [y/N] y
 Stream mapping:
   Stream #0:0 -> #0:0 (rawvideo (native) -> png (native))
 Press [q] to stop, [?] for help
 Output #0, image2, to 'out.png':
   Metadata:
     encoder         : Lavf57.76.100
     Stream #0:0: Video: png, rgba, 100x100 [SAR 1:1 DAR 1:1], q=2-31, 200
 kb/s, 25 fps, 25 tbn, 25 tbc
     Metadata:
       encoder         : Lavc57.102.100 png
 frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
 speed=9.16x
 video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 }}}

 When using `yuv420p` in the `color` filter, the output looks as expected
 (just with opaque background).

 This is somewhat related to #3302

--
Ticket URL: <https://trac.ffmpeg.org/ticket/6605>
FFmpeg <https://ffmpeg.org>
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