ffmpeg: insert bitmap subtitles as video in filters.

With this feature, it becomes possible to perform commonly
requested tasks, such as hardcoding bitmap subtitles.

This will be reverted once libavfilter has proper support
for subtitles. All the changes have the string "sub2video"
in them, it makes it easy to spot the parts.

1 files changed, 16 insertions, 0 deletions

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index 904a50589a..1ee42d82b4 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -989,6 +989,22 @@ ffmpeg -i video.mkv -i image.png -filter_complex 'overlay' out.mkv
 @end example
 @end table
 
+As a special exception, you can use a bitmap subtitle stream as input: it
+will be converted into a video with the same size as the largest video in
+the file, or 720×576 if no video is present. Note that this is an
+experimental and temporary solution. It will be removed once libavfilter has
+proper support for subtitles.
+
+For example, to hardcode subtitles on top of a DVB-T recording stored in
+MPEG-TS format, delaying the subtitles by 1 second:
+@example
+ffmpeg -i input.ts -filter_complex \
+  '[#0x2ef] setpts=PTS+1/TB [sub] ; [#0x2d0] [sub] overlay' \
+  -sn -map '#0x2dc' output.mkv
+@end example
+(0x2d0, 0x2dc and 0x2ef are the MPEG-TS PIDs of respectively the video,
+audio and subtitles streams; 0:0, 0:3 and 0:7 would have worked too)
+
 @section Preset files
 A preset file contains a sequence of @var{option}=@var{value} pairs,
 one for each line, specifying a sequence of options which would be