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

Bob Sully rcs at malibyte.net
Tue Sep 29 20:52:05 UTC 2009


Greg Zornetzer wrote:
> 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
>

Hi, Greg:

CPU is a 2.4GHz quad-core (Q6600) with plenty of RAM (8G - yeah, I know,
it's overkill but I had plenty of memory lying around out of another
machine, might as well use it).  Yes, I'm using VDPAU, and with the
6.5-10Mbit/s HD-PVR files I'm getting about 5-6% CPU (max) utilization. 
Mplayer is using all four cores (set as a default in ~/.mplayer/config). 
I probably should be using frequency scaling given that the box isn't
otherwise not that heavily used, but currently I'm not.

I do notice that on some recordings the delay gets progressively worse the
longer the file has been playing.

Thanks
Bob

-- 
________________________________________
Bob Sully - Simi Valley, California, USA
http://www.malibyte.net
http://www.malibyte.com



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