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Old 12-29-2005, 11:56 PM   #1 (Print)
haslip
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NY Fox Channel out of Sync?? or just me

for the last couple days, anything on my NY fox feed has the audio and video out of sync by just a tad. (channell 88)

I could of started when I got upgraded to the new LNB5 dish perhaps, is that possible?

My setup is and HD-Tivo with HDMI as the feed. But its happening on my new H20 also.

So I suspect either its the feed, or something to do with my new dish, despite a very high signal strength. Any thoughts??

Scott
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Old 12-30-2005, 03:37 AM   #2 (Print)
litzdog911
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There have been reports of audio/video synch issues with the new H20 DirecTV Receivers. But it seems you're seeing the problem on your HR10-250 also, so it's most likely a problem with the NY Fox station.

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Old 12-30-2005, 07:31 AM   #3 (Print)
wje
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This is a relatively common problem, and not just with DTV receivers. For some reason not apparent to me, the industry has never been able to figure out how to reliably sync audio and video in compressed data streams. Just how hard is it to encode time markers?

There are even some industry guidlines as to how much skew is 'ok', i.e., not objectionable to the average viewer, and a number of companies make deskewers for just this problem, although that's an expensive solution for just one station!

Anyway, there's no problem on your end. It's either the station, or DTV's uplink encoding. It's possible that the change is a result of the new MPEG4 locals rollout; DTV could either be using a different feed, or running through a new encoder.

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Old 12-30-2005, 08:05 AM   #4 (Print)
JimSpence
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I have also seen this with my non-DVR HTL-HD DirecTV receiver.

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Old 12-30-2005, 03:20 PM   #5 (Print)
TyroneShoes
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Quote:
Originally Posted by wje
This is a relatively common problem, and not just with DTV receivers. For some reason not apparent to me, the industry has never been able to figure out how to reliably sync audio and video in compressed data streams. Just how hard is it to encode time markers?...

It's actually very easy. The problem is that TV stations typically port audio around the facility as AES and video as SDI. They are completely separate systems, and while both are always locked to a house timecode reference, at any point where MPEG encoding or decoding must happen, which can be a lot of different points in the signal chain, the playback of video can slow down imperceptibly on its own, which can have a cumulative effect that is usually temporary. SMPTE is currently looking into ways to add extra metadata to MPEG video streams to marry them tighter to audio, but that solution is some time off (no pun).

Also, there are a lot of fixed delays in video processing these days. If the station is not careful about matching the delays by also delaying the audio, a somewhat permanent lipsync error can creep in. Email the station's engineering department directly, and CC the general manager.
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Old 12-30-2005, 03:48 PM   #6 (Print)
Paperboy2003
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Been happening for a while with both of my Hr10's

Seinfeld has been off by a lot...quite annoying if you're actually watching and not working and listening at the same time

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Old 12-30-2005, 10:48 PM   #7 (Print)
wje
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Quote:
Originally Posted by TyroneShoes
It's actually very easy. The problem is that TV stations typically port audio around the facility as AES and video as SDI. They are completely separate systems, and while both are always locked to a house timecode reference, at any point where MPEG encoding or decoding must happen, which can be a lot of different points in the signal chain, the playback of video can slow down imperceptibly on its own, which can have a cumulative effect that is usually temporary....


I'd think this would be trivial. If the timecodes were preserved in both streams, the decoder would only have to delay one or the other stream until the timecodes aligned. I suppose this would be much easier after uncompression, since the bit rate is variable in the encoded stream.

Jeez, the phone companies have been doing this for years... every cell tower in existence has time and frequency synchronization with every other tower or CO anywhere near it, and with every cell phone it's communcating with, usually with accuracies of close to 10e-11 Hz or better (which is pretty phenomenal, come to think of it). Wandering off topic even more, this used to be done with precision ovenized crystal oscillators, back when you could practically count the bits as they went by. Then they switched to atomic clocks, generally rubidium. Now, it's all done using GPS time signals (which are good to 10e-12, with proper processing). I've got one of each. Makes it easy to set my wristwatch.

Anyway, it's really annoying at times; be nice if they'd get their act together on this.

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