[mythtv-users] Force AC3 for HD-PVR?

Christopher Meredith chmeredith at gmail.com
Tue Jun 23 15:10:13 UTC 2009

On Tue, Jun 23, 2009 at 6:50 AM, Phil Linttell <phil.linttell at rogers.com>wrote:

> I have an SA4250HD, and I don't see any way to force the box to output AC3
> instead of AAC for stereo.  However, you can set the HD-PVR to encode AC3
> (even for stereo channels) as follows:
> v4l2-ctl --device=/dev/video0 --set-ctrl=audio_encoding=4
> It appears to get reset on system boot (or back-end restart?), so you may
> want to add it to rc.local.  Experiment first, however.  It would be nice if
> we could set this in the MythTV recording profile for the HD-PVR.
> I was trying to force the audio to AC3, as I noticed that the PS3 (DLNA
> front-end) doesn't seem to like stereo AAC stereo streamed from MythTV - I
> get no sound at all.   However, after setting the audio encoding as above, I
> recorded three programs in a row that would normally have been in stereo
> AAC, and the PS3  identified the audio as AC3 and played it fine - making it
> a pretty nice front-end for HD-PVR recordings.
> A caution though.... on my system (trunk 20737) the AC3 audio appears to
> break the preview generating process and results in a debilitating stream of
> messages on the back-end:
> 2009-06-23 05:59:36.862 [libfaad @ 0x7ff6cc838460]faac: frame decoding
> failed: Gain control not yet implemented
> 2009-06-23 05:59:36.862 [libfaad @ 0x7ff6cc838460]faac: frame decoding
> failed: Bitstream value not allowed by specification
> Anyone have any thoughts on how to fix this one?
> The other thing I haven't got to grips with is how to cut commercials out
> of the H264 recording....  I don't want to have to manually skip over
> commercials using the PS3 (ffd/rwd are a bit touchy anyway when streaming)
> so I'd really like to find a solution to cutting them out automatically.
> I've searched and it seems to simply be not supported for H264.
> I'm on Rogers cable in Canada, and all channels are encrypted, so all of my
> recordings are through the HD-PVR and in H264.

Thanks for that, I'll have to play with it. As far as commercial cutting,
see my writeup here:


I'm about to release an updated version of the script that has support for
show-specific folders and custom rules for specific shows on specific
channels. I've also been experimenting with lossless cutting using mencoder
and still have some bugs to work out.
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