[vdr] Re: Subtitle recording

[Lauri Pesonen <lauri.pesonen@firsthop.com>]

On Thu, 2002-06-13 at 11:27, Dave Chapman wrote:
> Is there any interest in adding subtitle recording (and obviously display in 
> the future) to VDR?  As with AC3 audio, it would be nice to implement 
> recording in advance of decoding and display functionality in VDR.
> 

I'm interested since in Finland two broadcasters provide all their
subtitling as DVB subtitles on at least five channels and it's a slight
problem with foreign programming.

> There are two types of subtitles used in DVB broadcasts - teletext and DVB 
> subtitles (ETS 300 743).  Teletext subtitles are relatively simple to decode, 
> but DVB subtitles are a lot more complex.
> 

I'm only interested in DVB subtitles since teletext subtitling is not
used in Finland. Does not mean that I could not help though.

> I can't find any channels on Astra 19 or Astra 28 that use the new, 
> bitmap-based DVB subtitles.  However, they are used with DVB-T broadcasts in 
> the UK, which is where I make all my recordings from.  These are broadcast on 
> a separate PID and this information would need to be added to the 
> channels.conf file, maybe separated by a semi-colon in the teletext field.
> 

As said above, Finland has at least five channels with DVB subtitling. 

I've been looking at the DVB subtitling and SI specs, but haven't really
yet figured out how to implement it. According to the specs the
subtitling PID should be read from the PMT segment. That means that if
VDR would be able to parse the PMT segments after a channel switch it
could search for the subtiling PID by itself. This would also enable the
use of multiple subtitling streams which could be selected via the
remote real-time. But I'm not really fluent with the DVB specs so I'm
not sure whether I've understood the subtitling stuff correctly.

> Would it be a large change to VDR to enable this kind of recording of "data" 
> streams?  It would add a small amount to the size of the recorded files, but 
> could easily be disabled.

Currently VDR does not handle any SI information during channels
switches. All SI related activity is done in the background in a
separate thread which uses the secondary cards for EIT gathering. Adding
the PIDs to the channels.conf file would be relatively simple, we would
not have to parse the PMT segments after a channel switch. I guess the
PID filter for the subtitling stream would be just like the video and
audio filters that are already set up during a channels switch.

Displaying the subtitles will be interesting, because of the limited
resources of the DVB cards. Whether to show the subtitles while the VDR
OSD is active etc.?

> Dave.
> 

br, Lauri