[mythtv-users] Commercial Blocker?

Joseph A. Caputo jcaputo1 at comcast.net
Fri Apr 30 09:29:22 EDT 2004

On Thursday 29 April 2004 17:45, Grant Edwards wrote:
> >> I haven't used it yet, but some say it's iffy still.  But once
> >> something's recorded, nothing is stopping you from fast-forwarding
> >> through the commercials.  Or editing them out altogether yourself.
> >>  And I wouldn't call fast-forwarding "watching" :-)
> >
> > Man it sure would be nice to be able to watch a 1 hour show in
> > about 30 minutes!    Can anyone explain how the commercial blocker
> > works?
> I've wondered that as well.  Does it assume that the CPU is
> doing encoding of the video stream or decoding of the ".nuv"
> file?  If so, does that mean the feature won't work with a
> PVR-350?

With software encoding, a 'first-pass' is made at blank-frame detection 
during encoding (recording).  If you try to skip a commercial on an 
in-progress recording (or one that has finished but not been flagged), 
you'll see an OSD for a while as it scans the frames looking for 
commercials, since they haven't been marked yet.  This is relatively 
slow, but still much quicker than watching the commercials.

After a recording has finished, a separate thread runs that goes back 
through the recording and detects/marks the commercials using a more 
finely-tuned process.  Once this process is complete, commercial 
skipping is instantaneous.

Since the commercial detection requires access to the decoded frames, if 
you're using a hardware encoder like the PVR-250/350, no commercial 
detection takes place during recording, as Myth never sees the decoded 
frames (they're encoded directly by the card and written to disk).  In 
this case you need to wait until the post-recording commercial flagging 
is done before you can truly skip commercials.  If you want to watch 
the recording before that, the jump keys come in handy!

Since the commercial cuts are merely stored as frame skip lists, 
commercial skipping works fine with hardware decoding like the PVR-350, 
Epia or XvMC.  Myth just won't feed the decoder those frames.


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