[FFmpeg-devel] [PATCH] lavc: add detection of forced subtitles

[Scott Theisen]

On 9/19/22 16:58, Hendrik Leppkes wrote:
> On Mon, Sep 19, 2022 at 10:53 PM Andreas Rheinhardt
> <andreas.rheinhardt at outlook.com> wrote:
>> Scott Theisen:
>>> This is from the following MythTV commits:
>>> libavcodec: add support for detecting forced subtitle segments. https://github.com/MythTV/mythtv/commit/5099f1a5777966fba482b623e581c1eef5c8fc09
>>> This adds forced subtitle segment detection to the PGS subtitle decoder and
>>> copies the result to AVSubtitle.
>>>
>>> Subtitles: Flag forced DVD subtitles. https://github.com/MythTV/mythtv/commit/78f71eecdbd53ba92af2ad639b32564c01f24563
>>> ---
>>>   libavcodec/avcodec.h   | 1 +
>>>   libavcodec/dvdsubdec.c | 4 +++-
>>>   libavcodec/pgssubdec.c | 4 ++++
>>>   3 files changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
>>> index 7db5d1b1c5..b9aa9efb2f 100644
>>> --- a/libavcodec/avcodec.h
>>> +++ b/libavcodec/avcodec.h
>>> @@ -2331,6 +2331,7 @@ typedef struct AVSubtitle {
>>>       unsigned num_rects;
>>>       AVSubtitleRect **rects;
>>>       int64_t pts;    ///< Same as packet pts, in AV_TIME_BASE
>>> +    int forced;
>> sizeof(AVSubtitle) is part of the public ABI, no additions to it are
>> possible. I wanted to suggest using AVSubtitleRect.flags, but apparently
>> AV_SUBTITLE_FLAG_FORCED already exists. And it seems that both the
>> dvdsub as well as the pgssub decoders already set this.
>>
> Which is also more correct, since in PGS for example you can have both
> active rects that are forced, and those that are not, at the same
> time.
>
> - Hendrik

Thanks for the suggestion, I'll look into switching MythTV to that. 
MythTV's handling of subtitles involves a few customizations to FFmpeg 
and I thought this would be acceptable.  Apparently not, and there 
already exists a method for this.

Thanks,

Scott