[mythtv-users] LipSync Issues with HDMI and 0.22

Jean-Yves Avenard jyavenard at gmail.com
Wed May 5 16:03:13 UTC 2010


On 5 May 2010 21:16, Jurgen Kramer <gtmkramer at xs4all.nl> wrote:
> I have the same problem when I switch my TV to 24Hz for 24fps films when
> playing with mplayer. What seems to help (workaround) is that when I do
> a fastforward while playing and then return to the original playing
> position with a rewind the lag is gone. I guess this is a caching issue
> of some sort.
> Nb when I play 24fps films with the TV still on 50Hz there are no
> lipsync issues.

The problem is that the refresh rate is never a perfect static value,
and there will always be syncing issues between the TV and the video

When your TV is set at 24Hz, the decoding + playback doesn't have much
latency to play with. If the video is playing slightly too fast, it
has to drop frames , if it's playing too slow it needs to seek
Calculating the proper timestamp to keep perfect AVSync becomes complicated.
That's why you will usually notice in the logs that myth is suddenly
playing twice faster to catch up or dropping frames.

When your TV is set at 50Hz, those issues do not occur and it's much
easier to keep thing working properly.

There is a patch somewhere for mplayer that improves things. I would
have thought it made it to mplayer by now. Have you tried a recent
mplayer ?

As for MythTV and AVSync, under some circumstances (especially with
timestretch active), there were errors in the timecode calculations
and there is work currently underway to improve the algorithm used for

I would expect that it won't be too long before this work gets in,
hopefully by 0.24


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