[mythtv-users] HD-PVR SPDIF audio trashed at beginning of recordings

[JS Boyd]

I found that if I used the slower channel change over firewire command:

mythchanger -f 7 -c

and added a 1 second sleep after that channel change that the noise 
disappeared.

But.... I get a new but more pleasant side effect: The audio will appear 
immediately in the recording and then disappear about a second or two 
into the recording and then begin again at the next scene change always 
within 3 to 10 seconds, which appears to be the next keyframe.

Thank you John for the info and insight.

JS.

John P Poet wrote:
> On Mon, Apr 6, 2009 at 2:55 PM, JS Boyd <mythtv at futures.com> wrote:
>   
>> Hello All,
>>
>> I was wondering if anyone else with an HD-PVR is getting from 1 second to 20
>> minute burst of static in the audio at the beginning of their recordings?
>>
>> It's almost always only about 1 second, but sometimes much longer. Once the
>> static disappears it never reoccurs within that recording. It's definitely
>> in the stream being passed to Myth. Playing the files with mplayer produces
>> the identical audio that the Myth Internal player plays. And given that Myth
>> does not process HD-PVR files while recording, I suspect it is the HDPVR or
>> maybe the cable box. Though directly connecting to the AV receiver via SPDIF
>> from the cablebox produces no static.
>>     
>
>
> Happens to me occasionally.  I have never had the static last more
> than 2 seconds, though.
>
> I was able to reduce the problem by waiting for the second "keyframe"
> in Myth's recorder before starting to "record" the stream from the
> HD-PVR.  However, that is the way it is in current trunk, so I am
> surprised that you are having much of a problem there.
>
> You could try H264Parser-fixes-v1.1.patch from
> http://svn.mythtv.org/trac/ticket/6243 .  With that patch, I actually
> get 1 second of static at the beginning *more* often then I do with
> the committed code, but it might work better for you.  That patch is
> actually more "correct" than what is currently committed to trunk.
>
>
>   
>> The HD-PVR is connected to a Motorola DCH3416 cablebox via SPDIF. The analog
>> audio is disconnected. I am using the latest driver from the Haupauge
>> website: 1.0.5.301
>>     
>
>
> I have mine hooked up to a Directv HD receiver.
>
>
>   
>> The static seems to always occur after a channel change, but even then it
>> does not always happen. I am using:
>>     
>
>
> I am guessing that the static is caused by the AC3 stream being in the
> middle of a frame when the recording starts.  So, it won't happen if
> the recording starts at the beginning of a frame.
>
>
>   
>> mythchanger -f 6 -c
>>
>> over firewire to change the cablebox channels.
>>     
>
>
> You could try adding a 1 or 2 second sleep at the end of the channel
> changing script.  I have a 1 second sleep at the end of mine, and that
> may be why this is not as much of a problem for me.
>
> It takes the HD-PVR a relatively long time to "sync" up with the
> incoming audio & video after a channel change (especially if the video
> resolution changes).  Myth wants to start processing the data from the
> HD-PVR *immediately* after the channel change script completes.
> Sometimes myth tries to process the data before the HD-PVR has settled
> down, and I think that may be part of the problem.
>
>
> John
>   


-- 
==
Ubuntu Feisty 7.04
MythTV 0.21-fixes 20018M+VDPAU+HDPVR_patches
AMD 64 x2 4200+ 65W Energy Efficient Processor
Abit NF-N2 nView Motherboard
NVidia 9500GT (VDPAU) fanless 1GB PCIe x16 videocard 
PVR-500 (Phillips Chipset)
 IVTV 0.10.4
HDHomerun /sys/version 20071120
Moto DCH3416 Cablebox + HDPVR & Firewire
4GB RAM
2- 500GB Seagate SATA: ST3500641AS Rev 3.AA
1- 1.5TB Seagate SATA: ST31500341AS Rev SD1B
SONY DVD RW AW-G170A