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Subtitle Offset Questions

Dec 20, 2015 at 6:15 PM
Just in the process of setting this up the first time and having some trouble getting the captions synced properly. I'm not using the commercial skip functionality, but I have instructed it to burn the subtitles into the video (as some of my DLNA devices don't pull down SRT files). The captions in the WTV files played back in media center are perfectly synced, but the converted videos seem to miss a few seconds of video (ie the converted files seem to start at about 5 seconds into the WTV version) so I'm guessing that is the source of the problem?

I'm currently waiting for it to reprocess an episode with the subtitle offset manually dialled in, but I'd like a better understanding of what is happening here? Specifically, is the underlying cause deterministic and this is a set it once and it always works thing, or is this going to need adjustment on a regular basis. Additionally, is there anything I can change in the profile settings to avoid it cutting off those first few seconds?

For reference, the system is running Win 7 with Media Center feeding from a HD Home Run tuner and Plex serving video to various devices. Other than adding the option to burn in the captions I'm using MP4 Normal profile. As far as options, I've disabled comskip, instructed it to capture the captions and changed the max width to 1280. Otherwise, settings are all default.
Dec 20, 2015 at 7:29 PM
What version of McEBuddy are you using?

The possible reason is a mismatch between the profile skip and GOP boundary lines. Let me explain

The profiles are setup to skip the first few seconds of the file (for stability). These are indicated by the -ss 3 for ffmpeg profiles and similarly for other encoders.
To compensate the default subtitle offset is set to 3 seconds so it'll be in sync.

However in realty even if you tell ffmpeg to skip 3 seconds. It doesn't exactly cut 3 seconds but rather along the GOP boundary line which can be +- 5 seconds depending upon the profile parameters. Hence it is never exact.

The answer is set the subtitle offset to 0 and remove the initial skip seconds from the profile and also from the remux profile in mcebuddy.conf. If you have good quality video recordings you don't need to skip initial seconds in the profile or the remux section (this was put in to manage bad quality recordings).

Hope this helps understand how it works.

Dec 20, 2015 at 7:48 PM
Version is 2.4.2

I'll give those changes a try - thanks for the quick response!

Most of the recordings will be coming from strong stations so I think that will work. We have a few weaker ones from across the lake that can fade out when the weather is bad, but typically I can get the same broadcasts locally in a slightly later time slot. Worst case scenario I can set a filter and process them separately (IIRC MCE puts the station name in the file name). Unfortunately, captions are one of those things that is really noticeable if they're even slightly out of sync so it's worth a little trouble.

Thanks for the great product!