Lip Synch Problem - Resolved

[elder]

I have noticed on several occasions a lip synch problem with my favorite program on GLC. When this happens in prime time I often just watch something else and since the program repeats three times in a 24 hour period I record one of the repeats for viewing and it's OK. Also, I have noticed that if I watch it the next morning it may be OK off the satellite. But to get to my question, tonight I was watching and recording on the DVR-1100c and a lip synch problem was obvious so my thought was to re-record during the wee hours. However, I went back to the recorded program after the network news just to confirm if I really wanted the program and found it to be OK. So, the question is what could be happening in the recording of a transport stream file that would alter the lip synch?

 

[Glorystar1]

During the playback of a prerecorded program the synchronization of the audio and video streams occurs during the initialization of the playback. If any error occurs during this syncing process, the audio and the video can playback out of sync. In this case, simply restart the program playback.

More often, the programming was transmitted out of sync and the transport stream was captured and is played back as it was received. This problem is most obvious with channels that are "turned" by an uplinker. The channel is received from another digital source (I.E. another satellite or fiber) and their head end receiver has lost AV sync. This out of sync programming then is retransmitted with the audio and video streams out of sync. If the programming was recorded out of sync, nothing can be done in the receiver to correct the playback. If the program is very important, the file could be corrected externally with a computer using an appropriate editing program.

The lip sync problem has been occuring more frequently with on our local over the air TV channels in the past months and I have had to call the stations on several occasions. Their engineers reboot the receiver or restart the file playback during a local insertion of commercials and when they return after a break, the lip sync is correct.

Goodbye to analog ghosting, snow and static! Welcome to digital with a new set of technical challenges!

 

[elder]

Maybe I was too wordy in my presentation. I was recording and viewing simultaneously when the lip sync problem was apparent. Later playback of that recording was OK.

 

[SatelliteAV]

Audio and video streams are synchronized by the receiver referencing a timing signal transmitted along with with the audio and video streams (PCR). During playback the receiver will look for this synchronization reference and coordinate the audio and video streams. Possibly the receiver had slipped sync during the real time viewing, but during playback the reference timing correctly synchronized the AV.

 

[jbmiller]

usually if you turn off wait 1 min then turn your receiver back on the sync problem will fix itself.
john

 

[Glorystar1]

Changing channels to receive another transponder then returning to the problem channel will force the dvb receiver to resync. Note: Resetting the power or changing channels will not correct the sync if the programming is being transmitted out of sync.

 

[elder]

Thanks, for the good information. It explains what could have happened in my situation and gives me suggestions of what to do if it happens again.

 

[elder]

I had emailed GLC prior to posting this thread, its answer was delayed due to the engineer being out of town. Here is his reply which confirms responses received here. GLC sells a system, so I don't know what brand of receiver he is addressing:

This problem, as you have noted, shows up occasionally when the audio and video lose their reference in the data stream. Normally this happens at one location or another and not across the whole network. To fix this problem we have found it is necessary to "glitch" the system enough to cause the satellite receivers to have to relock onto the signal. The problem can be caused at any number of locations but most often is a localized one. Next time it occurs try turning the power off on your satellite receiver. It may be sufficient to just turn it off using your remote control but we have found that at times it is actually necessary to use the switch on the back of the receiver or to actually unplug the receiver from the receptacle. This will cause it to reprocess the signal and lock back on to it.

 

[Cemguy]

I find that when sync is off on GLC, usually all it takes to resync is to switch to another channel on another transponder for a few seconds, then switch back.

 

[elder]

It has happened only once since I last posted, but a quick channel switch and return took care of it.

Thanks for all inputs, problem solved!