[mythtv] Commercial Detector questions

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Sat Dec 10 02:52:02 EST 2005

    Date: Fri, 9 Dec 2005 17:16:48 -0500 (EST)
    From: f-myth-users at media.mit.edu

    Another idea that might deserve some thought:  Looking for the sudden
    disappearance of closed-captioning information.

If anyone's inspired to actually try this, I just dug up a really
excellent tool that will help; it was mentioned a couple months ago
on the ivtv-devel list and I just found it.  Thanks to Hui Zhou for
writing this:


This tool produces timestamped ASCII text of the closed captioning,
suitable for input via the -sub switch for mplayer (assuming you've
made sure mplayer has OSD fonts and so forth).  Because it's indexed
to the stream, a commflagger should have no trouble noticing gaps in
the text and correlating it with whatever other visual processing it's
doing.  [Note that it assumes the format produced by ivtv (and maybe

This tool probably also solves another problem of mine, namely that
Myth doesn't preserve CC data when transcoding to MPEG4; it looks like
I'll be able to just preserve the CC data from MPEG2 in a separate
file and have mplayer redisplay it directly in the X video stream it's
generating (e.g., not by trying to embed CC data in NTSC line 21, as
the PVR-350's native MPEG2 output would do).  This is a little klunkier
because it requires frobbing mplayer to turn the CC on & off (and I
don't know if this can be done in mid-stream, so to speak), unlike
just using the TV controls to do it, but it'll probably do in a pinch.
And for machine-searchability it's actually much better to have this
data in a separate file from the much-larger MPEG anyway.

[Now my only problem is that the transcoder seems to be producing
files that have no audio and blow up mplayer after a few seconds;
that's a separate bug report.]

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