Lip sync (1 Viewer)

[grubi]

I did further research about the issue in the web and found some interresting things.
MP is not the only one having problems with it. I found a thread in the German "Dreambox" forum where you can read that Dreambox users have the same problem. Interrestingly they also supplied the reason why.

The broadcaster send the AC3 audio track between 60 and 160 ms earlier than the picture (different providers choose different delays) to give the devices enough time for processing the AC3 signal. As receivers are not equal in processing speed you then have to delay audio again in your setup to get into sync again. They choose this way as it is only possible to delay audio but not to speed it up. This gives also the explanation why this is only seen on AC3 and not mpeg audio because there is no processing necessary. The devs of the Dreambox implement an audio delay you can configure on a per channel basis.

I strongly vote for a similar configuration option in MP.

Regards,
grubi.

PS: here is a link to the discussion

http://www.dream-multimedia-tv.de/board/thread.php?threadid=674&threadview=0&hilight=&hilightuser=0&page=1

 

[ziphnor]

The broadcaster send the AC3 audio track between 60 and 160 ms earlier than the picture (different providers choose different delays) to give the devices enough time for processing the AC3 signal.

That doesnt really fit with my (admittedly limited) knowledge of how DVB broadcasting and DirectShow works. What we are receiving is an MPEG-2/4 transport stream. The data transmitted in this way is equipped with a 'Present' time stamp that informs the decoder when to present the data (and this might be some time into the future) (and similar time stamping is used in the DirectShow filter graph). The decoder should then process and buffer the data (whether audio, video or subtitles etc) until its time to present it. The idea is of course to send data sufficiently in advance to allow all relevant material to be decoded by the decoder. Therefore the exact amount of time spend by an AC3 decoder shouldn't matter, it should just be decoded and buffered until present time.

In addition, i would like to add that there might not be one single cause of the sync problem. As mentioned earlier in this thread all the physical AV components in the system (receiver, soundcard, TV etc) can all contribute in a small way to audio/video sync issues. That can then be compounded by software problems.

The lip sync issues i have encountered so far in MP are probably related to MediaPortal, or possibly buggy DVB card drivers. Im basing this on the fact that for example starting time-shifting can cause lip sync problems, and that occasional stutter in the image will result in an accumulated lip sync deviation.

If you guys want to test this you should try out another program for DVB viewing and see if you suffer similar lip sync issues everywhere.

 

[grubi]

The broadcaster send the AC3 audio track between 60 and 160 ms earlier than the picture (different providers choose different delays) to give the devices enough time for processing the AC3 signal.

That doesnt really fit with my (admittedly limited) knowledge of how DVB broadcasting and DirectShow works. What we are receiving is an MPEG-2/4 transport stream. The data transmitted in this way is equipped with a 'Present' time stamp that informs the decoder when to present the data (and this might be some time into the future) (and similar time stamping is used in the DirectShow filter graph). The decoder should then process and buffer the data (whether audio, video or subtitles etc) until its time to present it. The idea is of course to send data sufficiently in advance to allow all relevant material to be decoded by the decoder. Therefore the exact amount of time spend by an AC3 decoder shouldn't matter, it should just be decoded and buffered until present time.

In addition, i would like to add that there might not be one single cause of the sync problem. As mentioned earlier in this thread all the physical AV components in the system (receiver, soundcard, TV etc) can all contribute in a small way to audio/video sync issues. That can then be compounded by software problems.

The lip sync issues i have encountered so far in MP are probably related to MediaPortal, or possibly buggy DVB card drivers. Im basing this on the fact that for example starting time-shifting can cause lip sync problems, and that occasional stutter in the image will result in an accumulated lip sync deviation.

If you guys want to test this you should try out another program for DVB viewing and see if you suffer similar lip sync issues everywhere.

I agree that there are different causes for different kind of audio sync issues. What I'm talkink about is the problem that different channels show different behavour. E.g in my setup ARD is always in sync and SAT.1 is the most worse. Interrestingly audio comes alway to early and not to late and MPEG audio is always in sync on all channels. I only see this problem with AC3.

Any suggestion what app to test to further track down the problem?

Regards,

grubi.

PS: Only having this problem with DVB - DVD playback is always as accurate as it can be (DD and DTS)

 

[ziphnor]

I agree that there are different causes for different kind of audio sync issues. What I'm talkink about is the problem that different channels show different behavour. E.g in my setup ARD is always in sync and SAT.1 is the most worse. Interrestingly audio comes alway to early and not to late and MPEG audio is always in sync on all channels. I only see this problem with AC3.

At my end i havent really noticed any variation in the problem based on channels, but there could easily be multiple issues involved.

Any suggestion what app to test to further track down the problem?

DVBViewer is nice, but its not free ( http://www.dvbviewer.com/en/index.php )

I would probably try MyTheatre's trial edition ( http://www.dvbcore.com/ ) its full featured except for exiting after 1 hour which is probably not that important for testing this. Its also doesnt install any annoying services etc, which is nice when you only need it for testing / comparison.

Otherwise try one of the following:
http://www.gbpvr.com/
http://www.altdvb.ro/
http://www.progdvb.com/

 

[grubi]

At my end i havent really noticed any variation in the problem based on channels, but there could easily be multiple issues involved.

Any suggestion what app to test to further track down the problem?

DVBViewer is nice, but its not free ( http://www.dvbviewer.com/en/index.php )

I would probably try MyTheatre's trial edition ( http://www.dvbcore.com/ ) its full featured except for exiting after 1 hour which is probably not that important for testing this. Its also doesnt install any annoying services etc, which is nice when you only need it for testing / comparison.

Otherwise try one of the following:
http://www.gbpvr.com/
http://www.altdvb.ro/
http://www.progdvb.com/

Thank's for suggestions.
I will do some tests at the weekend and post back the results. Maybe this gives a clue what is MP related, what is driver related and what is provider related and at least if there is anything usefule we could do to compensate in MP.

Regards,

grubi.

 

[Taipan]

I will do some tests at the weekend and post back the results.

Did you come to any conlusions about the cause of the poor lip-sync?

I have tried all sorts of variations (different video decoders, different audio decoders, different audio renderers), but have not been able to identify a hard "cause and effect" relationship, except that the lip-sync is noticably worse when I watch HD (720p, 1080i) channels. In fact, the lip-synch will start out OK, but then get progressively worse over the first 20 minutes until it is unwatchable. Flicking to another channel and back again will cure the lip-sync for about another 20 minutes ...

I would use TVE3 (as it is reported to be free of lip-sync issues) but the recording of mpeg files in TEV3 is flakey ...

 

[grubi]

I will do some tests at the weekend and post back the results.

Did you come to any conlusions about the cause of the poor lip-sync?

I have tried all sorts of variations (different video decoders, different audio decoders, different audio renderers), but have not been able to identify a hard "cause and effect" relationship, except that the lip-sync is noticably worse when I watch HD (720p, 1080i) channels. In fact, the lip-synch will start out OK, but then get progressively worse over the first 20 minutes until it is unwatchable. Flicking to another channel and back again will cure the lip-sync for about another 20 minutes ...

I would use TVE3 (as it is reported to be free of lip-sync issues) but the recording of mpeg files in TEV3 is flakey ...

The lipsync issue is not so easy to track down because lipsync is only a symtom for which one or multiple causes may be responsible. From what I have found so far TV3 did not suffer from some of the issues TV2 additionally have (esp. when timeshift is enabled) so first I would go the TV3 route. Then you should make checks if audio is in sync seperately for AC3 and MPEG audio. MPEG audio should be in sync all the time. AC3 maybe somewhat to early on some channels. If you encounter this problem I did not find a way to fix this with MP as some providers send AC3 a lot earlyer (100 to 200 ms) to give additional time for processing but MP does not seem to resync it again (there is also no option to manually delay AC3 on a per channel basis). As last resort if you pass AC3 to an external receiver you could check if your receiver has a AC3 delay option, however as delay varies for every channel this is not very comfortable.

BTW: Some other DVB Receivers suffer from exactly the same problem. E.g. I found that some Dreamboxes are affcected to. There developers have added the possibility to delay audio manually on a per channel basis.

grubi.

 

[Taipan]

I did some more tests over the weekend and I am beginning to think that the lip-sync problem is a 'feature' of the particular Video decoder used and TVE2.

For example, I used the TV viewing software that came with my Dvico Fusion DVB-T card and it was able to play all SD and HD channels without any perceptible delay in the lip-sync.

So then I configured MediaPortal to use the same Dvico DxVA video decoder, and again I could not notice any lip-sync issues. The problem with the Dvico DxVA video decoder is that it won't work with .dvr-ms recorded files and the de-interlacing is not as good as with other video decoders.

If I use the Intervideo (WinDVD 8) video decoder, the lip-sync is terrible, but it works with all SD and HD channels and the de-interlacing is fine.

If I use the Cybelink (PowerDVD 7) video decoder, the lip-sync is better, but it won't work with some HD (1080i) channels.

And, if the corruption problem with TVE3 recorded mpg files didn't exist, then I would switch over to TVE3 immediately.

 

[grubi]

The lipsync problem with TV3 and AC3 audio on some channels is much less present compared to some weeks ago. Not sure if it is related to changes made in one of the latest svns or something that changed on the provider side (KDG).

 

[xuxo]

unfortunately i'm also affectd by this problem. I have the standard MP Client TV Engine with DVB-C / Floppy DTV running here. i can also confirn, that some germany channels are really bad on that!

Anyway did somebody try to eliminate this issue by using reclock?

I'm not sure if reclock runs well with MP or is able to solve that.

regards.