[mythtv] Re:Help: trying to trace channel/DVB problem

Simon Watson simon19720 at yahoo.co.uk
Wed Jun 25 11:43:18 EDT 2003

Ben, thanks for your response on this.

Let me update you on where I've now got to (and hopefully help others who might
end up in the same situation)...

Rather than hardcode a return value for the channel inputname, I simply changed
the capturecard.defaultinput and cardinput.inputname DB fields to empty
strings, which allowed the CheckChannel SQL query to complete successfully. I'm
pretty sure that this is a firm requirement of the current codebase.

Having done this, I was pleased to see mythbackend proceed to detect my DVB
driver and start trying to tune in to my start channel. I had to tweak a few of
the fields ("3_4" instead of "FEC_3_4" etc) but it then tuned successfully.
Mythfrontend then displayed a picture but it was running at 1-2 fps and
completely unwatchable. Whilst I was fairly convinced that 'use_ts' should be
1, I took your advice, changed it to 0, and, hey presto, a great picture with
working sound! 

So, firstly let me thank you (and others) for your efforts with DVB support in
getting things this far. There are, however, a few serious gremlins which I
still need to resolve:

* Changing channel to one with a different frequency (mux), causes the backend
to segfault, and the frontend to lock tight.

* There is occasional & noticable slowdown in framerate from time to time.

* On one occasion, mythbackend reported the infamous "Backend stuffed up in 
RequestRingBufferBlock" error. I left mythfrontend running overnight and this
morning it had happened again so there's a problem somewhere (DVB driver,

* Changing channel to one with the same frequency takes 2-3 seconds and causes
some quite bad picture breakup when the new channel appears. Not a killer, but
doesn't look as slick as a regular STB.

* Several of the DVB-T channels here in the UK (Freeview) are transmitted in
16:9 aspect ratio. Myth seems to be scaling these to 4:3 (as I would expect) so
this might be something for the MythTV project to tackle at some point in the

Obviously, the channel changing is the biggest issue for me. I updated my CVS
on the 23rd June, so it should have the recent patches. 

Again, any pointers/tips would be much appreciated. Happy to try and help
improve/fix things where I can.


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