[mythtvnz] Recordings without audio

[Stephen Worthington]

On Tue, 8 Nov 2016 11:25:30 +1300, you wrote:

>On Sun, 06 Nov 2016 01:32:17 +1300
>Stephen Worthington <stephen_agent at jsw.gen.nz> wrote:
>
>> On Sat, 5 Nov 2016 21:44:35 +1300, you wrote:
>> >Occasionally shows are recorded without any sound. Others on the same channel are fine. E.g.: TV3, recording 'Graham Norton' and (immediately following) '7 Days' - the first is OK, the second silent. I have two tuner cards; perhaps MythTV switches from one to the other between shows? The 'silent' problem only happens infrequently, maybe one show per month, so if it was a faulty tuner, I would expect to see it a lot more often. Anyone have any ideas?
>> 
>> As of MythTV 0.28, the database stores which card was used to make a
>> recording.  If you use the I key twice on a recording and scroll down
>> a bit, you see a field called "Recording Input".  This does rely on
>> your having set the displayname field for each tuner when you created
>> them.  If you did not do that, run mythtv-setup and add a displayname
>> that is different for each tuner.
>> 
>> Also, check when you play a 'silent' recording if it has alternate
>> audio tracks.  It may be that by default you are playing the wrong
>> audio track, and if a particular recording has more than one, the
>> others are not actually valid and do not have the proper sound.  Or
>> possibly there is 5.1 or 7.1 sound and your sound setup does not
>> handle that properly and produces no sound, where it works for a
>> normal stereo sound stream.  While playing, M > Audio > Select audio
>> track shows the list of available audio tracks.  Recent TV3 programmes
>> usually have both an AC-3 5.1 audio track and an AAC stereo track.
>> Older programmes (ones recorded a few years ago, but broadcast
>> recently) may only have AAC stereo.  TVNZ 1 programmes seem to have
>> both AAC and AC-3 audio, plus a second AAC audio track marked as
>> Italian language.  I have a feeling that if you play the Italian
>> audio, it will not actually be valid, but I have never actually tried
>> that.
>> 
>> If you have a 'silent' recording hanging around still, then you might
>> like to install the mediainfo package then run the mediainfo command
>> on the file for that recording, and post the results.  To find the
>> recording file for a particular recording, use the I command twice on
>> it and scroll down to the "Recorded File Name" field.  Then look for
>> that file in each directory where you store recordings.
>
>Many thanks for that clear explanation. Doing the 'select audio track' fixed it, so at least I now have a work-around.
>
>I'm a little puzzled that most times the same show is OK. Is is broadcast with different audio tracks on different occasions, or do I (as I suspect) have the default set differently for the two tuners, and the 'good' one is usually randomly chosen for the recording? Where can I set the default track to record/play?
>
>I'll try the mediainfo next time I get a silent recording.

When you record a programme, MythTV records all the streams for that
programme, including all the audio streams, subtitle streams and so
on.  It does not matter what tuner is used, all the streams will be
recorded.  On playback, you get to choose which streams are actually
used for playback.  So it may be that you have the wrong default set
for which audio track is played back.  I am not sure where in the
settings that will be though - it is a very long time since I last
played with the audio settings.  The option to select the audio track
manually will always be available as long as there is more than one
audio track recorded.

It is also possible that the problem lies outside MythTV.  What path
does your audio take between the recording file and your ears?  Do you
have an external amplifier and speakers, are you using SPDIF output,
or HDMI to the TV itself, or any one of a myriad of other possible
setups?  To fix this problem, we need to know what the capabilities of
your specific audio path are, and then match the MythTV audio playback
settings to them.  It is also possible that you may need some alsa
settings changed.