Captions slowly go out of sync over time

[pastro]

I use mpg2srt to rip the captions and the srt viewer to show them. It works fine, except on a 1 hour show the captions start to show up too early the further into the show you go. If I use the line21 decoder via graphedit they are timed correctly. Any ideas how to prove whether this is the SRT viewer or the captions themselves that are not correct?

Edit: I made a test file at 1 hour and 1:30 and the captions looked like they came up exactly right. Seems like it must be an mpg2srt issue. Anyone else see this?

[pastro]

I'm sure mpg2srt is not getting the timeline right. I used a different extractor and the captions are correct at the end of the file. The timestamps in the files start out about -500ms and they end up at 3 seconds off, or a total of 3.5 seconds of drift. Since I slip 3.5 seconds the captions from mpg2srt appear to be extracted at this rate: 1/3596.5*29.97*3600=30hz.
Which would give the 3.5 second shift over an hour

Unfortunately ccextractor isn't quite ready for primetime since it created one caption with a line full of spaces which the srt viewer didn't like. I'm sure it threw the srt parser off. I manually fixed it and the file played fine but it won't work without another program to fix the output.

[sub]

Sorry, I dont think there is anything I can do about this one. It does sound from you analysis like mpg2srt isnt getting it quite right.

[pastro]

Sorry, I dont think there is anything I can do about this one. It does sound from you analysis like mpg2srt isnt getting it quite right.

I can write a post processor that fixes the captions, but I need to check some more data to make sure it's always off 3.5 seconds for an hour or if it is some other anomoly that makes mpg2srt slide.
I'm still curious though if anyone else sees this.

[pastro]

I PM'ed Merrypig about the problem and he said that the playback is running at 30hz and the timestamps are at 29.97 which causes the drift. He might build in an option to ignore the timestamps.
Sounds like the 29.97 to 30hz conversion (drop a frame here and there) causes the issue since there is no mechanism to fix the srt file which is generated at 29.97.
Seems like any playback that does frame rate conversoin is going to have this issue.

[sub]

GB-PVR isnt doing any frame rate conversion though, so the recording should be playing back at the original frame rate. This makes me think its some logic error occurring in mpg2srt.

[pastro]

GB-PVR isnt doing any frame rate conversion though, so the recording should be playing back at the original frame rate. This makes me think its some logic error occurring in mpg2srt.

Gbpvr might not be, but the video card or the player has to. The display is 60hz. I believe that causes the trouble with the srt file being out sync. Course that said, I don't see why ccextractor works correctly. Maybe they do the conversion on the timestamps.