Audio sync problems with Live TV

[Barsk]

I have had this problem for a long time now and tried several ways to cure them, i.e trying a bunch of different decoders, both for video, audio and audio renderer but I am stuck! I've discussed this with Sub and he claims the problem is due to the combination of decoders and audio renderer. But I have tried everything I can think of and I am out of options...

The problem occurs ONLY with Live TV on AC3 (Dolby Digital) channels. When timeshifting or viewing recorded shows the problem goes away.
With the AC3 track channel I get bad sync with approximately up to 500 ms. But not always! Sometimes the sync is perfect. Sometimes the sync is better, sometimes worse. In timeshift mode however perfect all the time...

Soundcard is a Realtek ALC883 with latest drivers with S/PDIF out to a receiver that decodes PCM and AC3 tracks. MP2 sound on the other channels is decoded to PCM by ffdshow or similar before going to the receiver. The tuner is a Twinhan DVB-T PCI decoder.
Channels with MP2 sound does not have sync problems.

I would really like to cure this problem as it is driving me nuts. Any insight anyone?

My current setup is PowerDVD 8 video decoder, ffdshow audio decoder and Realtek HD Audio audio renderer.

[fiteclub]

Barsk,

Unfortunately, I don't have an answer; as a matter of fact, I am having almost the same problem. I can usually get rid of the sync problem by changing the channel and coming right back to the one of interest. Many times this works for the entire time I am watching; but sometimes the sync drifts out again. Very annoying. Recordings are always in sync for me; however, timeshift for me is so bad that its pretty much unwatchable. Weird that it magically works if the entire program is already recorded. These problems ONLY occur for me using the HDHomerun source. All my analog sources behave perfectly all the time. I too have tried a variety of decoders and renderers. The best that I have found is the nvidia video and audio decoder and "system default" as audio renderer. I could never get ffdshow, Dscaler or AC3filter to ever work very well for me. Others always tell me that is sounds like a "mux" problem, but it is my understanding that a mux is not used during liveTV mode. I see no place in PVRX2 config to select a mux anyway. I don't think it is the same thing as the BDA multiplexer that is on the Misc 2 tab.

My audio is S/PDIF from an on the motherboard Realtek audio chip.

Just wanted to let you know that you are not alone in your frustration.

Bill

[sub]

Others always tell me that is sounds like a "mux" problem, but it is my understanding that a mux is not used during liveTV mode. I see no place in PVRX2 config to select a mux anyway. I don't think it is the same thing as the BDA multiplexer that is on the Misc 2 tab.

The "mux" is the BDA Multiplexer on the Misc2 tab. A mux is being used whenever you're recording, including timeshift live tv. The files produced by some muxes are better at playing back while recording than other muxes, so it could certainly be a factor in what you're seeing. Try the Microsoft DVR-MS mux - its usually pretty well behaved.

[Barsk]

The "mux" is the BDA Multiplexer on the Misc2 tab. A mux is being used whenever you're recording, including timeshift live tv. The files produced by some muxes are better at playing back while recording than other muxes, so it could certainly be a factor in what you're seeing. Try the Microsoft DVR-MS mux - its usually pretty well behaved.

Just a reminder to those trying the DVR-MS mux. It works perfectly on a single computer. However if one wants to use a client setup such as an NMT (e.g Popcorn Hour) or the older MVP from Hauppauge or even another GP-PVR from another computer in client mode in a LAN you cannot use the DVR-MS mux. There is a sticky thread discussing and linking to several versions of different muxes. If you have problems with timeshift, the source of those problems is very often a bad mux!

The mux is not used on Live TV, but when producing an mpeg file for timeshift or recordings. And of course only for BDA sources (DVB, i.e digital TV).

Hmm, I tried the new built-in ts mux when I last upgreaed to the newest GB-PVR. I don't remember exactly what was the problem with it for me, but i skipped it for a Cyberlink mux instead. I might have been mistaken though... What is the status of the TS mux today? Is it reliable?

[Barsk]

Barsk,

Unfortunately, I don't have an answer; as a matter of fact, I am having almost the same problem. I can usually get rid of the sync problem by changing the channel and coming right back to the one of interest. Many times this works for the entire time I am watching; but sometimes the sync drifts out again. Very annoying. Recordings are always in sync for me; however, timeshift for me is so bad that its pretty much unwatchable. Weird that it magically works if the entire program is already recorded. These problems ONLY occur for me using the HDHomerun source. All my analog sources behave perfectly all the time. I too have tried a variety of decoders and renderers. The best that I have found is the nvidia video and audio decoder and "system default" as audio renderer. I could never get ffdshow, Dscaler or AC3filter to ever work very well for me. Others always tell me that is sounds like a "mux" problem, but it is my understanding that a mux is not used during liveTV mode. I see no place in PVRX2 config to select a mux anyway. I don't think it is the same thing as the BDA multiplexer that is on the Misc 2 tab.

My audio is S/PDIF from an on the motherboard Realtek audio chip.

Just wanted to let you know that you are not alone in your frustration.

Bill

Thanx Bill,

good to hear others are suffering from similar problems. I'am not sure what media type HDHomerun is, but i conclude it is DVB in some sorts. In that case we are in the same boat and suffering from similar problems. The common thing here is the sound card, a Realtek. May that be the source of the problems? I am running the absolute latest drivers from Realtek's web. the 2.02 version. But I have had the same problems with earlier versions too.

The BDA driver for my Twinhan card is the latest the last time a checked, sometime early this year. I have tried Nvidia purevideo drivers too but no luck.

[fiteclub]

The "mux" is the BDA Multiplexer on the Misc2 tab. A mux is being used whenever you're recording, including timeshift live tv. The files produced by some muxes are better at playing back while recording than other muxes, so it could certainly be a factor in what you're seeing. Try the Microsoft DVR-MS mux - its usually pretty well behaved.

Sub,

Thanks for clearing that up, I installed the LEAD mpeg2 mux but it does not show up in the drop down on the misc2 tab. Are only certain muxes supported? Also, I see sync problems in liveTV mode with NO timeshifting used. Since a mux is not in use what else could cause it? It seems to happen on all my digital channels which are all dolby digital sound. Recorded channels play perfectly using the DVR-MS mux so this seems to get the mux off the hook. The only fly in the ointment is the severe sync problems in timeshift mode. I would love to use timeshift mode but it is too bad to put up with. Could it be that my PVR/video card needs more horsepower (specs are in my signature) I currently must use overlay for the video renderer to have smooth HD playback.

Thanks,

Bill

[sub]

Sub,

Thanks for clearing that up, I installed the LEAD mpeg2 mux but it does not show up in the drop down on the misc2 tab. Are only certain muxes supported?

Yes, only certain muxes are supported. They're proprietary and work in different ways, so GB-PVR has to build in support for each type of mux. Some mux download links can be found here: http://forums.nextpvr.com/showthread.php?t=25630

Also, I see sync problems in liveTV mode with NO timeshifting used. Since a mux is not in use what else could cause it? It seems to happen on all my digital channels which are all dolby digital sound.

The usual cause of audio/video sync issues is the decoders you're using, but it could potentially also relate to the audio renderer.

Recorded channels play perfectly using the DVR-MS mux so this seems to get the mux off the hook.

Some muxes produce files that are easier to play back while still recording, so it may not be 100% off the hook.

When testing timeshift, I definitely think its worth trying both DVR-MS and TS Mux, and one of the .mpg muxes like the Cyberlink one.

The only fly in the ointment is the severe sync problems in timeshift mode. I would love to use timeshift mode but it is too bad to put up with. Could it be that my PVR/video card needs more horsepower (specs are in my signature) I currently must use overlay for the video renderer to have smooth HD playback.

If your machine is already struggling, then its possible the extra overheads of live tv are pushing it over the edge in some way.

[AndyPro]

The only time I end up with this problem is when I have AC3Filter encoding stereo stuff to surround, then feeding it to my surround receiver. Theres a setting in AC3filter to offset the audio from the video however much you want, but that doesn't help because my issue is that it starts out perfect and drifts off moe and more as time goes on.


The way I've found to fix it is to let my receiver do the conversion, rather than the computer. I just output everyhting raw straight out the optical jack (of a realtek onboard sound). If it's already a surround stream, it outputs it as a surround stream. If it's a stereo stream, it outputs the pcm but then the receiver turns it into "enhanced 5 channel" somethin or other. You can also use things liked dolby pro logic and pl2 which actually work quite well, relatively.

Basically, I offload as much as I can from the computer. It's not like I'm getting bogged down either...my CPU never goes above 4% in sd, and 20% on one core in HD. It's just the fact that if you're processing, you're offsetting. To really see what I mean, hook up some speakers tot he analog out of the card, and also listen, at the same time, to the digital out of the card. Makes some really nice reverb effects but is very difficult to listen to :p

--Andy P

[fiteclub]

Andy

I offload audio stream via S/PDIF to my receiver for decoding but I still get sync issues. Thanks for your comments

Bill

[Barsk]

Just an update on the situation for me. I changed the Audio Renderer to System default and the problem was (mostly) solved. So, it seems Sub was right again... As always... Sorry about that.

However, there are still some sync problems at times, just as reported in the first post. The delays are just that magnitude smaller now, but still somewhat erradic. Sometime spot on, sometimes a few tenths of milliseconds off. I would say around 50 ms. Not that much, but enogh to throw lip-sync slightly off.
When I go to timeshift - always spot on. This occurs it seems with AC3 sound channels only. I use S/PDIF out and no decoding on the PC.

So, there is still some problems. Don't know how to progress from here though... Might Vista solve this?