[mythtv] dvb zero length record

[William Uther]

On Fri, 20 May 2005 17:55:08 +1000, Phil Vid <phil.vid at gmail.com> wrote:

> I'd just like to update everyone with my ongoing investigations into
> the zero byte dvb recording phenomenon.
>
> There appear to be 3 distinct causes of the problem:
>
> 1. Blank recording, nothing obvious in the logs case 1. This appears
> to be a keyframe detection problem. The recordings enter the
> ReadFromDMX() loop but silently exit as no keyframe has been detected.
> The obvious symptom of this is the absence of the message 'DVB#x Found
> keyframe' in the log. I will investigate this first as this is the
> cause of 90% of my zero byte recordings.

[snip]

> Any ideas, especially on case 1, would be really helpful. I saw there
> was some discussion from Jesper and William Uther regarding this issue
> but I'm not sure what the outcome was. I'll start digging through the
> MPEG specs now.

As Tom mentions in his email, I'm not sure this is the complete list  
of causes for the zero length record.  My discussions with Jesper  
were about picture starts not occurring at the start of PES packets.   
The code now searches through all payload for picture start codes.

I assume you're talking about DVBRecorder::ReadFromDMX().  In the  
section starting "if (_record_transport_stream_option)", I assume  
that _keyframe_seen is not being set for you.  Is that right?  That  
is normally set in DTVRecorder::HandleKeyframe(), and I haven't  
touched that code.

The first thing I'd try would be to turn off the "Wait for Keyframe"  
option for the tuner card.  Does that help?

Be well,

Will          :-}