Subtitles (TTXT) getting "lost" after ad-breaks.

Clumpco

Member
Build 629d
ITV Granada HD .ts

I have recently been having some problems with subtitles. On shows where there is an ad-break (removed) the subtitles do no seem to pick up after the break. There is some stream corruption (due to snow) so often there are 200-300 frames removed... but not around the ad-breaks.

If I change the edit-point of the offending ad-break by an I-Frame or two the subs sometimes carry on to the next break (but get lost there).

Strangely if I open the .ts that has been output, VRD doesn't find the subs at all (mediainfo says that they are there). Also VLC won't play the .ts.

Any ideas?
 

Dan203

Senior Developer
Staff member
Is the ad break right at the start of the file? Or in the middle?

Subtitle streams are tricky. Unlike audio and video streams they are not interleaved into the file in any consistent pattern. They're sort of randomly inserted whenever they're needed. Because of this VideoReDo can not specifically look for, or wait for, subtitle packets during output. It simply passed them along as they're found.

So what can happen is sometimes the source stream will have the subtitle packet inserted before the frame you selected to make your cut on. And since we only output from the cut point forward that subtitle packet is skipped. If this happens right at the start of the file, where you make your first cut, then the player may not detect that there are subtitles in the file and will ignore subsequent subtitle packets even though they are there. However if it happens in the middle of the file then it may skip one subtitle right after the break but it should recover once it hits the next one.

Unfortunately there is really no way for us to correct for this. The DVB subtitle format has no standard for where or when the subtitle packets have to be inserted so there is no way for us to know where, or if, they are in the stream.

Dan
 

Clumpco

Member
Is the ad break right at the start of the file? Or in the middle?Dan
Usual UK ad-breaks at approx 10, 30 and 45 minutes.

Thanks for the explanations, I am wondering if ITV haven't changed their encoders/muxers recently.

I will see if it continues, but it's certainly a new phenomenon, in the past VRD has always done a fine jubs with subtitles.
 

Shannock9

New member
This is an old thread, but if anyone comes here with the same problem...

...you can use the technique I explained in this forum How to do J-cuts/L-cuts with VRD to make a THIRD edit of the same length with the subtitles packets included.

AFAIK you will then need to use Project X to extract the subtitles to feed to your authoring program. This is probably too long winded for regular processing of TV episodes, but it can work if you are desperate. Happy editing
 
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