[vdr] Re: Questions about the subtitles-plugin

[Pekka Virtanen <pekka.virtanen@sci.fi>]

"so-8859-1?B?SORt5GzkaW5lbiBKb3Jp?jori.hamalainen"@teliasonera.com wrote:
> > Ahh, hmm, thanks. I can't say I understood you too well, but 
> > I'll experiment when I get home. You'd improve your UI if you 
> > 'grayed out' the delay setting when the "sync=yes".
> > And if the UI also said what the delay is and what '10' 
> > means, it'd start to be understandable..
>
> Should I try again:
>
> Sync option means that should the plugin try to sync to DVB timestamps
> (== PTS, presentation time stamp, DVB video&audio frames have them).
>
> On "yes" setting it tries, but there are some problems and
> you can see what they are by searching "getstc" on mailing lists.
>
> On "no" plugin doesn't sync to DVB-video, it generates timing
> (how long should subtitle be on screen) based on operating system clock.
> Delay is after how long plugin should 'delay' the subtitle before
> presenting it. Without delay plugin would show it at once subtitle
> is received to buffer (seconds too early compared to audio/video).
>
> subtitle comes at (wall clock): 15:20:00.00
> subtitle start pts (dvb timestamp) = 123.00s
> subtitle stop pts = 124.50s
>
> So subtitle should be shown 1.5 seconds according the DVB-stream.
> Now we have this delay variable, I don't know if it is 
> # of frames  or 1/10second or 1/100second but I guess it is 1/10 second.
> And based on my guessing "delay = 20" means delay of 2 seconds.
>
> Subtitles plugin will put subtitle on screen (wall clock): 15:20:02.00
> And remove from screen (wall clock): 15:20:03.50
>
> Pekka Virtanen, the osd-subtitles author, can clarify more & correct 
> my (miss-)believes :-).
Well I'm not sure if anybody is interested but here is some technical 
explanation about the synchronization.

Synchorinization: on

while (sub_pts < stc(t))
  wait;

(STC is coming from the mpeg-decoder)


Synchornization: off (More accurately fake stc)

stc(0) = first subtitle's pts
time(0) = "wall clock" time the first subtitle was received

stc(t) = stc(0) + (time(t)-time(0)-delay)*90000;

while (sub_pts < stc(t))
  wait;

The delay is from the configuration.

90000 is the frequency of the system clock.




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