WTV H264 Closed Captions > MPEG2

sheppy99

New member
Is VRD likely to support closed captions in the near future from H264 WTV > MPEG2? If so would you like any test files?
 

Dan203

Senior Developer
Staff member
Captions/Subtitling in WTV is tricky. We can read NTSC captions and DVB subtitles from WTV files, but not Teletext. Teletext captions are stored in a proprietary format which we have not been able to decipher. Saving captions/subtitles to WTV is even worse. We can save 608 captions with MPEG-2 video by interleaving it into the video frames. However it does not work with other formats because MS uses a special "spanning event" to signal the start of caption/subtitle streams but does not expose a method for actually adding one of these "spanning events" in the SBE writer that applications like VRD use to write WTV files. So we can actually store captions/subtitles in a WTV stream, but because the "spanning event" is missing MCE does not recognize that they are there. We've sent emails to MS asking for a way around this, but so far have not received a reply. :(

Dan
 

sheppy99

New member
I think it's DVB captions I'm after and from WTV H264 to MPEG2 MPG, not the other way around. It's really to improve my comskip accuracy so not a big problem.
Thanks for the reply and please let me know if you'd like some samples to play with.
 

Dan203

Senior Developer
Staff member
DVB subtitles will be saved if you output to MPEG-2 TS. The Program Stream format (i.e. .mpg) does not have a way to store subtitles other then DVD subtitles which we don't currently support at all.

Dan
 

sheppy99

New member
Interesting, the TS file does according to the video program display have the extra stream but for some reason comskip doesn't see it. Is there any way of checking that there is anything within the stream?
From the program display:

Subtitle: 1-1
Type DVB Subpic PID 0x23A
Language eng Page 1
 

Dan203

Senior Developer
Staff member
First you need to make sure VRD is actually picking up the subtitles. Open the original WTV file in VRD and then click the view menu. If the subtitles are available then they will be listed at the very bottom of that menu. Select one of the streams and then play the video. If there are actually any subtitles in that stream they will display in the video window. (must be using VMR7 or VMR9 for this to work)

If you verify that there are subtitles in the original file then try playing the TS file in VLC. It should show the same subtitles that you saw when playing the WTV file in VRD.

It's possible that comskip only supports text based captions, and not subtitles. Especially if it prefers .mpg files which do not support DVB subtitles at all.

Dan
 

sheppy99

New member
Just did a test, subtitles present in the original WTV, but only in the converted MPEG2 TS file if the resolution was the same, and they display in a smaller font. In the lower resolution converted file they were available to select but they didn't show on the screen when playing back the file.
Is this what you'd expect?
 

Dan203

Senior Developer
Staff member
It's funny I was actually just reading the DVB subtitle spec for another project and I was wondering what would happen if the user recoded the video to a lower resolution. DVB subtitles are image based, so they are designed to match the resolution of the original video. When you reduce the resolution of the video in VideoReDo we have no way to reduce the size of the subtitle bitmaps to match. They are simply passed through, as-is, which creates a discrepancy between the actual video resolution and the target resolution of the subtitles. The only way to make this work properly would be to resize the subtitle bitmaps to match the new video resolution. Unfortunately that's not currently possible in VideoReDo.

I'm going to have to talk to DanR about this, but we may end up disabling DVB subtitle output if the video resolution is being changed. At least until we can work on more robust subtitle handling which allows us to resize the subtitle bitmaps to match the new resolution.

Dan
 

sheppy99

New member
Makes sense, odd how it uses a bitmap rather than a data stream. Unfortunately Comskip can't see it so perhaps it's not worth pursuing for my scenario. I'll email Erik and ask what it supports.
 
Top Bottom