Tvheadend

Converted teletext SRT-file in recorded MKV, yes. Sorry for not being clearer.
The channel is Canal+ in Sweden but this is true for all such recordings I've done from several different channels.

I don't understand. What has this got to do with the mkv spec?
Is the problem with TVHeadend or somewhere else?
The subtitles are now pretty much completely useless.

Henrik,

what tool did you use to extract the subtitles from the tvheadend recorded mkv?

tvheadend writes converted teletext subtitles as simple ascii subtitles. And in the teletext specification there is no concept of "duration" so that is why tvheadend does not write a duration in the subtitle track. And the mkv specifications does not mandate a duration for these kinds of subtitle track.

Hein

Hein,

they were extracted with MKVExtract(GUI). Playing any such recording in either VLC or MPC (Windows) shows subtitle tracks all right, but shows no actual subtitles onscreen simply because their duration is exactly zero.

I have been using VDR for many years which records the teletext stream, from which you extract the subtitles with for example ProjectX into an SRT subtitle file. There subtitles have their correct durations.

/Henrik

Basically, I suppose this is how it works:

A page with subtitles appear in the teletext. This is converted to a subtitle with it's start time.
As the subtitles duration is over, the teletext now updates to a blank page. This is converted to a blank subtitle with that start time.

The resulting subtitle should set the duration, or end time, to co-incide with the next updated pages start time.

I've been using tvheadend/XBMC for the last 12-18 months and it works very well. I really like the (relatively) small footprint of tvheadend, when compared to the overly complicated MythTV setup, that I've used for a couple of years before my change to tvheadend. Of course there are some features of MythTV that I miss (to some extent), like "timeshift", "advanced record scheduling" and the possibility to order a recording (from the remote) of the TV show currently being watched as live-TV. The last issue is mainly a client issue, but I've implemented a small patch to tvheadend (2.12) and a little "lirc" client-utility (to act on the record-button) to enable that "time-to-go-to-bed-feature"...

However, there is one problem with tvheadend (2.12) that I really would like to be solved (or solve myself if more spare time was available). The problem is the "limited" functionality of the teletext subtitles (according to this thread). I'm also using DVB-C in a house connected to the comhem network in Sweden. About half of the channels in my subscription uses teletext subtitles and the behavior, when using XBMC to play such channels (live-TV or recordings), ranges from "almost OK" to "very bad". When it is at its very best, the subtitles appears in time, but they're newer blanked until next subtitle (can be minutes depending on scene). For certain channels (like "Showtime"), maybe 1 subtitle out of 10 will (visibly) appear. Hopefully I'll have time to look at this, but my wife (and my 3 kids) always put other activities at a higher priority level...

/Libbe

I have the same problem here. I have a channel which broadcasts both Teletext as well as DVB-C subtitles, and neither is usable. When I recorded the same channel previously using MythTV (to MPEG-TS), it worked just fine. There must be something in the mkv conversion that's screwing it up.

if you record using MPEG-TS the unaltered mpeg stream including the dvb subtitles are stored unaltered in that recorded file.

Tvheadend is not using MPEG-TS to store the recordings but mkv. This is because an mkv file can contain meta data which can not be stored in a MPEG-TS file.
Because of the use of mkv a methode to store the dvb subtitle stream had to be build. The dvb subtitle stream is added as a S_DVBSUB stream to the mkv. But at the moment there are no players around that can use this datastream to playback the dvb subtitles.

Next to the S_DVBSUB stream tvheadend also contains logic to store the teletext subtitles as simple S_TEXT/UTF8 subtitles inside the mkv.

Because of the way teletext subtitles work and the way tvheadend creates the mkv streams it is difficult/impossible at the moment to specify the display time of a teletext subtitle inside the mkv.

I hope this clarifies the way subtitles work at the moment.

Hein