[mythtv-users] HD-PVR no audio (aac instead of ac3 on SPDIF)

[John P Poet]

On Wed, Jan 5, 2011 at 7:54 PM, Michael Rice <mikerice1969 at gmail.com> wrote:
> Since upgrading to Fedora 14 and .24-fixes I am getting some
> recordings without audio.
>
> The log shows that it thinks it is aac instead of ac3:
>
> Stream #0 pid(0x1011) type(video-h264  0x1b)
>  Registration Descriptor: 'HDMV' Blu-Ray A/V for read-only media (H.264 TS)
>  Stream #1 pid(0x1100) type(audio-aac  0xf)
>
> A correct recording would be:
>
>  Stream #0 pid(0x1011) type(video-h264  0x1b)
>  Registration Descriptor: 'HDMV' Blu-Ray A/V for read-only media (H.264 TS)
>  Stream #1 pid(0x1100) type(audio-ac3  0x81)
>  Registration Descriptor: 'AC-3' ATSC audio stream A/52
>
> It seems to be happening in about 5-10% of my recordings but later recordings
> with the same tuner seem to record fine.
>
> I didn't have this issue with Fedora 12 and 0.22-fixes.
>
> There was a thread on this in July but it wasn't clear if there was a solution.
> I have my Motorola cable boxes locked at 720p and just use 6200ch to
> change channels with firewire.  I never had to have a sleep in my channel
> changes but would adding that help here?  Any other ideas to resolve this?


It is possible that a sleep (even just 1 second) would fix this.  The
HD-PVR can do some strange things when told to start recording, and
the signal from the STB is not "crystal" clean.

In 0.24, Myth does it's best to wait for "clean" video, but there is
no way to wait for "clean" audio.


> I build from source so if someone has an idea on how Myth could detect this
> and restart the recording I'd be interested.  Or even detect it and abort the
> recording.  At least in that case I'd have a chance to restart the recording
> myself before it is over.

The problem with trying to detect this, is some channels (usually
standard-def) don't have AC3 audio.  With the optical audio input, I
believe the HD-PVR just muxes in whatever audio it sees --- I don't
think it re-encodes non-AC3 into AC3 the way it will with the RCA
audio inputs.  So, failing when the audio is not AC3 would not be a
proper solution for everyone.


John
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