[linux-dvb] Interesting DVB-T issues

["Edward Wildgoose" <Ed@Wildgooses.com>]

(well, I thought so...)

First, I haven't run scan for perhaps 6-12 months, but for various reasons
ran it again recently, and just happened to notice that quite a few of the
channel tuning details have changed..!  This is for the crystal palace
transmitter in the UK and quite a few of the channels now have different fec
values for both hp and lp params.

Now is this because a previous version of scan was not returning proper
values or is this something which I should have been looking out for?

The practical upshot is that after correcting these I now get instant,
perfect audio-video sync on BBC ONE and BBC TWO using "mplayer dvb://" and
all the other channels exhibit symptoms of just starting out of sync and
gradually audio/video synchronise over a few seconds.  Previously I had a
lot of issues with ITV 2 and having the updated tuning params has helped
enormously.

However, that audio-video sync brings me to my next observed peculiarity.
Basically, BBC ONE and TWO have instant and perfect audio/video sync in
mplayer, but the other channels appear not to have video pts and so players
like mplayer seem to gradually bring everything back into sync, presumably
based on the audio timestamps.  This corresponds with BBC ONE and TWO being
the only two with the PCR pid being the same as the video pid, and the other
channels have an independent PCR pid.

The PCR pid does seem to be significant because once I add this to vdr's
channels.conf file then vdr can get instant audio-video sync without the
usual few seconds gradual alignment that otherwise happens.  Can anyone
confirm this behaviour for them?

Also, are there any references as to how the PCR stream should be used in
the ts2ps type process?  It's not obvious where this is done in the VDR code
for example...

Anyway, if you are in the UK and using DVB-T then it seems worthwhile
checking your channels.conf settings from time to time to make sure it up to
date!

Thanks all

Ed W



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