Lip sync (1 Viewer)

[grubi]

To track down the problem I made some further tests with the following results:

1.) Lip sync issue seems only to be seen on AC3 aduio; mpeg audio does not show that problem.
2.) There are a few channels where this problem doesn't exists (Das Erste - ARD)
3.) There are channels where this problem is distinctive (SAT.1).
4.) I tested three different soundcards and different drivers but thas does not solve the problem.
5.) I tested different codec combinations but that does not solve the problem.
6.) The only way solving this problem seems to use ReClock.

grubi.

 

[dekkers]

I do have also have lip sync prolems when using SPDIF. This also occurs on my Samsung DCB360R settopbox.

It looks like this has something to do with SPDIF. When I use on my settopbox the HDMI link for sending audio to the television there's no delay in it, when using SPDIF (to the amplifier) it has delay. I didn't figure out yet why this is happening.

I've seen this more then once on different A/V setups. Most of the time it's hardly noticeable, but when focusing on it you can see/hear it.

 

[grubi]

I do have also have lip sync prolems when using SPDIF. This also occurs on my Samsung DCB360R settopbox.

It looks like this has something to do with SPDIF. When I use on my settopbox the HDMI link for sending audio to the television there's no delay in it, when using SPDIF (to the amplifier) it has delay. I didn't figure out yet why this is happening.

I've seen this more then once on different A/V setups. Most of the time it's hardly noticeable, but when focusing on it you can see/hear it.

It also seems to depend on the quality of the channel. From what I have found on other forums often AC3 is not muxed accurately in sync on DVB so it's the repsonsibility of the decoder to get it insync again.

grubi.

 

[nexsen]

Lip-sync error is very common but insidiously masks itself from most people because sound before the event that caused the sound is impossible in the real world and our brains can't handle the confusing and contradictory aural and visual information.

Research at Stanford proved it causes a negatiuve impact on viewer perception making the characters seem more agitated, less successful, less persuasive, etc even when not consciously noticed so those who see it and correct it should not only eliminate the annoyance but eliminate that disruptive albeit subliminal force that plagues essentially all home cinema's.

You've already noticed it but most people who haven't noticed it are probably looking away from the lips subconsciously avoiding this contradiction of nature or perhaps there is some other avoidance mechanism but whatever it is must be the root cause of what Stanford documented.

Because of this difference in the detection capabilities of different people this is a very hard topic to discuss on a forum since we do not all perceive the same lip-sync eror even though we might be viewing the same thing. One person doesn't see 40 ms error and I am now bothered by one millisecond so how do we converse on this subject?

For others reading this post that don't believe what I am trying to say, conduct this test:

Force your self to really look at the LIPS. You will probably be amazed at the lip-sync error you previously ignored which will prove some sort of avoidance mechanism is in play. Some people will find this very hard to do since they have seen very little material that was truly in-sync to compare.

Usually most people won't notice 40 or 50 ms (Stanford showed 42 ms still caused the impact on perception) but when a new DLP, LCD, or plasma display adds another 50 or 60 ms the 100 ms plus error may be consciously noticed and after that much smaller lip-sync error becomes annoying.

Luckily three companies: Alchemy2, Felston, and Primare make digital audio delays expressly for the purpose of correcting this problem and here is a review of all three:

http://www.audaud.com/article.php?ArticleID=3011

The most important feature of all of them are the plus and minus buttons which allow on-the-fly fine adjustment of audio delay without disturbing the image you are watching and all of them have that. The other features like presets, etc. are nice but the plus and minus button adjustment without disrupting your program is the main thing you need for perfect lip-sync.

Lip sync error creeps into media starting at image capture and continues through post production and broadcast or DVD encoding and is often well above the 42 ms Stanford showed causes interference with perception before the media center even gets the signals so even if the media center were perfect and introduced no video delay there would still be significant lip-sync error. The only way to eliminate it is by subjectively matching the video delay with the same audio delay.

 

[grubi]

Very interresting link. Since the first time I noticed lip sync I'm always looking after it even if I don't want to and I get really annoyed if I detec even the smallest non sync.

grubi.

 

[nexsen]

You may be interested in reading the research report from Stanford that documents the negative impact on perception leading audio causes:

http://www.pixelinstruments.tv/pdf/Articles/Effects of Audio-Video Asynchrony.PDF

It seems incredible this has been known for 14 years.

 

[Taipan]

I have been plagued by lip-sync issues recently too (using TVE2) - I watch only DVB-T and I have noticed that some channels will start out fine and then over the next 10 to 20 minutes, the video will lag the audio by up to 300 mS (my estimate). Changing off that channel and back again will usually correct the lip-sync, but it will drift out again. Having timeshift ON or OFF makes no difference.

I haven't noticed if it is only AC3 audio that is affected - I will do some tests over the next few days to see if I can narrow the particular conditions. I will also make some recordings to see if they are affected, too.

I have tried all combinations of video and audio decoders, but with no improvement.

The fact that I have only been aware of this lip-sync problem in the last couple of months suggests that it was introduced in a SVN release. I can't be absolutly sure, but I think it was fine with v0.2.3.0RC1 (no SVN). I guess I could go back and try that version, just to be sure.

 

[nexsen]

That's a good idea since our own perception and sensitivity to lip-sync error changes as our exposure to larger lip-sync error reduces our threshold of recognition.

 

[ziphnor]

I remember having lip sync issues much earlier than 0.2.3.0RC1, and when it happens it can easily be up to nearly a second out of sync (!) but usually its much less.

I noticed that lip sync usually happens in correlation with image stutter, for example the small stutter that happens as you turn on time shifting, change a channel or encounter a poor signal situation. As previously mentioned here, changing the channel or turning time shifting on/off will sometimes solve the problem.

As others have mentioned, i don't believe there are lip sync issues in TVE3, or at least i dont remember noticing it.

 

[grubi]

I can acknowledge all that has been written here. It would be interresting to find out if this problem is caused by MP or if other software is also affected. In my setup (DVB-C) it also depends on the channel. ARD is allways in sync whereas SAT.1 is the most worse. Switching channels or audio track sometimes reduces or eliminates the problem. I only ecounter it with AC3. No problem so far with MPEG audio. There is no difference if using TV2 or TVServer3. There was a long open mantis case about exactly that issue, but it has been closed a week ago as not beeing reproducable (IMHO there must be more users out have it but they do not recognize it).

On other forums I have found that different providers take more or less care about the sync issue on broadcasting an rely on the playing devices to correct this issue. This seems to be correct as I do not have this problem with the built in DVB-T receiver of my TV-Set.

Is there an option in MP to manually configure delay for audio?

grubi