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TCM HD Channel 789 on Comcast audio out of sync again

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It is 4:56 PST and TCM HD on Comcast is channel 789.  Have been trying to watch ''The Racket" but is wldly out of sycn --audio and video.  But not on SD TCM channel 501.


I'll call Comcast but will, as usual will be useless.   M

Stephen L

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I advised Comcast.  Hopefully they will corrrect.  Am now watching 'Too Late for Tears' on Comcast TCM Std Def 501.  Again, due to HD 789 HD way out of sync.  Might only be in my Comcast region (Santa Cruz, CA)



Stephen L


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Comcast TCM 789 Is back in perfect sync as of this morning (when I turned on 'Giant' about an hour ago.).  Comcast recommended I have a tech install a new cable card.   I will if it goes out of sync again notwithstanding no other channels do. On the  other hand, due to no ohter postings,  I must assume I'm the only  one who experienced this on TCM HD 789 last night (PST).  So a mystery why back in sync.



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  • 4 years later...

For the cable transmission, there are separate audio and video frames encoded into the digital stream.  They don't get locked together like the sound and picture on a 35mm film, mainly because they aren't side-by-side like that.  Instead they are in a single-file stream, with no mechanism to synchronize them, other than to receive everything perfectly.  On a good digital stream where A/V is in sync, there is a disproportionate amount of more video frames to audio frames, in random circumstantial order.  So it isn't something that has any obvious solution.

Due to the way streaming video works, If a packet is dropped on the network, there is no attempted recovery.  Then it is out of sync.  Changing the channel can temporarily alleviate this.  There are sometimes groups of channels sent together, so you might need to go several channels away, then back.  This forces the receiver to  communicate with the local cable plant and reset that multi-channel stream (for more on these groups of channels, look up SDV - "Switched Digital Video").  Last I looked into it, a typical cable service had both individual digital channels for the more commonly watched lower channels, and SDV on the lesser-watched upper channels.

It seems cable SD channels aren't as prone as HD channels, perhaps due to lesser demands on bandwidth.

Some local areas are worse than others, with more local cable network congestion and not enough equipment to meet those needs.  Depending on the cause, the network equipment might be able to be tweaked or altered to meet those needs.  Sometimes just getting newer specification cable wiring in your house might be the solution, like if you have had it for over 10-20 years.

On top of that, the cable channel would sometimes go blank on its own, unrelated to any power savings features.  This seems logical to be a related SDV issue, with interrupted communications between home and cable plant, in which the cable plant likely monitors the home DVR to see if it's still powered up and in use, then shuts off the stream if it doesn't get a reply - for the sake of bandwidth conservation on their network.  This is evidenced by the TV screen occasionally going blank as I am watching it - even though the DVR is still powered up and no power savings features are in use...

For those reasons I became a satellite viewer 4 years or so ago, and haven't replied to any of the dirt cheap cable offers to go back.  The satellite transmission chain is incredibly simple - it is just point-to-point up to the satellite and then back.  Also, unlike cable and Internet where every single connection requires one-to-one (individual) 2-way communication, satellite is a one-to-many transmission - just like local broadcast TV.  It doesn't matter how many or how few customers are trying to use it at the same time.  So unless there is a rain fade during a heavy storm, or potential hard drive issue with the DVR, it is usually really good.


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