[mythtv-users] HDPVR audio out of sync in 5.1 AC-3 mode

[Greg Zornetzer]

Hi Bob,

On Mon, Sep 28, 2009 at 6:44 PM, Bob Sully <rcs at malibyte.net> wrote:

> > Date: Sun, 27 Sep 2009 12:53:28 -0700
> > From: Greg Zornetzer <gzornetzer.lists at gmail.com>
> > Subject: Re: [mythtv-users] HDPVR audio out of sync in 5.1 AC-3 mode
> >
> > Hi Oz,
> >
> > On Sun, Sep 27, 2009 at 12:29 PM, Oz <ozdror at adelphia.net> wrote:
> >
> >>
> >> When I change my Sat Box from PCM to Dolby digital and the HDPVR Audio
> >> encoding to 4 (AC-3). The audio is significantly lagging behind the
> >> video (possibly 2 seconds)
> >>
> > You cannot send 5.1 PCM over SPDIF (either toslink or digital coax) -
> only
> > stereo PCM is available.  5.1 can only be sent over TOSLINK compressed as
> > AC3 or DTS.  This is why you get only stereo when setting the box at PCM.
> >
> > Potentially dumb question - If you hook up the Sat box directly to the TV
> > and the audio to a surround receiver, do you still observe the 2 second
> > offset?  If so, it's the source's fault and not the HDPVR.
> >
> > -Greg
>
> I have noticed this same problem when recording from the HD-PVR.  It seems
> to be variably bad (sometimes almost no delay, other times bad enough
> (say, 2 seconds or more, as noted above)) to make it annoying enough to
> just delete the recording.
>
> I am recording at 720p with the 5.1 optical input to the HD-PVR from the
> STB.  I am recording (using a bash script I wrote) from the command line,
> as I am not running trunk.  I am using JYA's version of 0.21-fixes, with
> the VDPAU updates.  Before switching to the 5.1 optical output, I did NOT
> have this problem when recording in stereo from the RCA inputs.   However,
> I want to find a way to fix this rather than going back to 2ch audio, as
> transcoding files with the 2ch audio track was problematic.
>
> Unfortunately, I can't test this with my 5.1 stereo receiver, as its
> optical audio inputs recently went to hell (I'm looking into a new
> receiver).  The input from the Myth box into the receiver is via digital
> coaxial, which does still work fine.  I do NOT get these delays with 5.1
> recordings from the HD HomeRun or the pcHD-5500, so my guess is that it IS
> the HD-PVR.  However, the recordings aren't consistently bad.
>
> Anyone else have a clue as to what's causing this?
>
> Thanks!
> Bob
>
> Given Oz's note that dropping the bit rate helped him, are is your CPU
overloaded?  If you bring up 'top' in a console window on the frontend, what
is the CPU load?  What CPU do you have?  Are you using VDPAU?  Are you using
CPU frequency scaling on that box?  What bit rate are the recordings?
HDPVR recordings will take a lot more horsepower to decode as compared with
recordings from the HDHomerun, due to the different encoding.
Good luck,
-Greg
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