[mythtv] Accuracy of external subtitles

[Brooks Whiteford]

On 3/9/10, Jim Stichnoth <stichnot at gmail.com> wrote:
> I have noticed that when using external subtitles in MythVideo
> (through a .srt file), synchronization starts off fine, but after
> jumping forward or backward, synchronization is usually off, and
> subtitles display too early, anywhere from about a half second to 5 or
> 6 seconds early.  The offset stays consistent as long as there is no
> jumping -- there is no drift and it looks like subtitles are turned on
> and off correctly except for the shift.  This also happens when
> starting playback from the bookmark.
>
> I checked TextSubtitles::GetSubtitles() and it appears that the
> subtitle timecodes are correct and that the timecode argument passed
> in is being matched to the correct subtitle.  It appears that the
> timecode argument does not necessarily represent the actual frame
> being displayed.  I tried running "mythcommflag --rebuild --file ..."
> in case it's a seektable issue, but that didn't help.  There are
> comments in NuppelVideoPlayer::DisplayTextSubtitles() warning about
> subtitles being out of sync, but I don't see how those warnings would
> explain timecodes changing as a result of jumping around within the
> same playback instance.
>
> I've never seen anything like this with EIA-608 closed captions, and I
> use them all the time.  It seems that EIA-608 captions use
> GetLastShownFrame()->timecode whereas text subtitles use
> GetLastShownFrame()->frameNumber.  Are these fields allowed to be
> inconsistent?
>
> Any thoughts/comments on this?
>
> Jim
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