Wednesday, May 23, 2012

MythTV and the Phantom Soundtrack

I previously reported that, having installed Mythbuntu 12.04 and a Hauppauge WinTV-DCR 2650 (and with Comcast as my cable provider), I was getting a spurious soundtrack on one channel (ABC).  When I tested the setup by watching live TV through it, ABC was showing "Spiderman 3", and I was hearing the dialog in Spanish.  It turns out that was the only time I heard Spanish.  Thereafter, whenever I tuned to channel 3 (ABC), the audio was an FM station continuously broadcasting the local weather (?!).  All other stations had the expected audio track.

After considerable poking around, I still don't know why I'm hearing the weather station (or why it was the Spanish dub of Spidey 3 that one time), but I have identified a pattern and a workaround.  It turns out that a random sampling of the stations I tune in (which form a proper subset of the stations available through my Comcast subscription -- my channel list excludes stations I never watch) put them into four categories:
  1. some have a single audio track;
  2. some have two audio tracks, with no sound on the second track;
  3. some have two audio tracks with the same contents on both tracks (at least same to my ears -- if one is higher quality than the other, I'm not detecting it); and
  4. ABC (only) has two audio tracks with that weather station on the second track (except, apparently, when it's something else).
In all cases the first audio track has the correct (for me) contents.  Apparently MythTV defaults to the highest numbered track (which is fine for cases 1 and 3) but is smart enough to avoid an empty track when it sees one (so no problem with case 2), which just leaves me with the single instance of case 4.  I don't know if a given station always falls into the same category, or whether in cases 2 and/or 3 the contents of the second track change if, for instance, a movie that has been dubbed into another language is showing.  (Anyone know if any of the "Star Trek" franchise movies have been dubbed into Klingon?)

The pop-up menu (triggered by the 'M' key on the keyboard or the 'Menu' button on the remote) has a submenu to control audio during playback, and for ABC I can use that to switch to the first track.  It's a mild annoyance, but nothing serious.  Searching online yielded other concerns about MythTV defaulting to the highest numbered track, but no solutions other than manually switching.  So for now, at least, I will just have to live with switching audio tracks whenever I replay a recording of an ABC show.

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