[mythtv-users] Recording digital-audio channels over FireWire appears to not work in MythTV

[Scott Alfter]

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The local cable system has a bunch of audio channels up in the 900s with music,
talk radio, etc.  Out of curiosity, I tried recording from them over FireWire
with the same tools that grab HD channels and such.  With the cable box set to
one of the audio channels, it spits out a transport stream containing just an
AC3 audio stream--no video.  test-mpeg2 captures this stream with no problems.
 mplayer should be able to play it; I know it can demux it and dump the AC3
stream to a file (use the -dumpaudio option, with -dumpfile to specify an
output filename).  The AC3 file can then be played as-is or converted to
another format.

The talk-radio stream I grabbed as a test looks like it's encoded at 128 kbps.
 The graphics displayed on the cable box's analog outputs are generated by the
cable box.  They're not part of the incoming stream, which is why the captured
stream contains only audio.

Where MythTV comes into this is that it you would think that since it's capable
of recording from FireWire-equipped cable boxes, it'd be able to grab these
audio-only streams.  It would appear that the lack of a video stream confuses
mythbackend, though, as you end up with a zero-byte file.

I know that radio != TV, but it seems to me that this could be a nice extra
capability that probably wouldn't need much extra work to get it working right.
 I suspect there are some sanity checks of the incoming stream that are getting
confused by the lack of video; disabling these checks for certain channels (and
disabling other processing, such as commercial flagging, that won't work
without video) would get the job done.

  _/_
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