Fox locals splicer burp

[TomCat]

For a couple of months now, I have noticed a freeze and audio mute coming out of local breaks and going back into the network. I started to notice it when I started to record FOX shows via MPEG-4 sat channels rather than OTA using a HR20. Local video freezes, audio burps with zipper noise, video goes to black for a second, and then upcuts the network. Sometimes it happens going the other way (net to local).

This is not a local station issue, as I have made simultaneous recordings OTA on the same HR20 of the same program also recorded as MPEG-4. They are clean. LIL is not.

Since FOX is deriving their SD locals from the HD locals, the same problem is seen on their SD bcxes.

FOX uses a Terayon MPEG/AC3 splicer to insert local ASI directly into the FOX ASI bitstream. MPEG splicing is not perfect when the two streams can not be timed to each other, and since one originates from the network while the other originates locally, and since MPEG is elastic, such timing is not easily done, and so far has not been done by FOX afffils. The splicer crashes the running GOP and compensates by dropping or repeating frames, so that the switch appears to be synchronous, but it is still never perfect, because the reconstruction of the truncated GOPs done on the fly still has problems that might not pass certain decoders gracefully.

There is a theory that there might be an incompatibility between the MPEG splicer at FOX stations and the Harmonic MPEG-4 encoders used by DTV. I assume the problem has been there since locals were added.

My question is have other viewers of FOX prime or sports HD programming on LIL locals noticed this problem also?

TIA for responding.

[videojanitor]

TC,

I have not noticed this on the LIL feed I receive from KTVU in the SF area. I just went back and checked a couple of things I recorded this week, and there is no freeze or mute going in or out of the local breaks. Now before you ask, yes, for reasons I won't state publicly, I do know that these were the local breaks I was looking at. ;)

The only problem I see on KTVU is that their splicer TIMING is way off. By that I mean, the splicer configuration can be adjusted so that the local and network streams are coincident, thus at least giving you a fighting chance of having the "switch" occur in the right spot (though as you said, the switch point is "elastic," so there's always going to be a +/- error). However, theirs is off by at least a second or more every time -- you will often see a segment start in SD for a second, then start again (repeating that same second) in HD.

Now, that said, watching several FOX stations OTA with various tuners, I have noticed that some of them tend to hiccup at the splice point. I used to have one that would mute about a second BEFORE the spice happened -- could always tell when the local break was coming. So, perhaps in your area, DirecTV is using an off-air receiver that is having a similar problem when it encounters the splice, and that upsets everything else down the chain? One thing that I know can cause problems is if the local station doesn't send 5.1 during local, or if the bit rate is different from the network.
That can cause a disturbance at the splice, which may or may not upset things.

Hope this helps!

[t_h]

All my locals have the audio brrrping on a regular basis, sometimes within the show so its not a transition thing.

When I've talked to directv about it, they've said it was the local stations problem so there was nothing they could do about it. The local stations said it was directv's problem so there was nothing they could do about it, and cited local broadcasts and cable carriers not having the problem with their signal. But of course those are in mpeg2.

[evan_s]

I have seen the so called Brrps altho for the most part I try to ignore them as much as possible since that seems to avoid getting annoyed as much as possible. Some of the times it seems to consistently be occurring would definitely seem to support this belief but it definitely does happen at other points.

Personally I think your theory is probably correct or at least very close in that slight issues in the mpeg2 stream that don't cause significant problems as is get amplified when the encoder converts it to mpeg4 and makes it noticeable. A solution can and should come from both ends. The stations should be trying to minimize these minor mpeg 2 issues as much as possible and at the same time DirecTV and Harmonic need to be improving how the mpeg4 encoders handle these minor mpeg 2 issues.

[veryoldschool]

This seems to be related to this thread: http://www.dbstalk.com/showthread.php?t=152754

[Mavrick]

The answer I gave in the other thread at least with my local fox station the problem was found to be caused by the exciter on their OTA transmitter.

http://www.dbstalk.com/showpost.php?p=2014625&postcount=148

[mgmrick]

Syracuse fox is horrible...The other networks are better but not perfect. How long before this is fixed? I spend 130 month and may look at my other options if that does not change this has been going on way too long

[TomCat]

This seems to be related to this thread: http://www.dbstalk.com/showthread.php?t=152754Possibly, but I specifically do not want to equate this with non-specific glitches. I am specifically talking about those only at net>local>net transitions from FOX affils.

[TomCat]

The answer I gave in the other thread at least with my local fox station the problem was found to be caused by the exciter on their OTA transmitter.

http://www.dbstalk.com/showpost.php?p=2014625&postcount=148Sorry, again, a different problem. That thread is from 3 years ago. The problem I am speaking of only began here when LIL HD became available in this market, and migrates now to SD because the MPEG-4 HD is the source of the LIL SD, rather than the old analog source.

But thanks just the same :)

[R0am3r]

Syracuse fox is horrible...The other networks are better but not perfect. How long before this is fixed? I spend 130 month and may look at my other options if that does not change this has been going on way too long

The problem at WSYT used to be a lot worse. When the local engineers added the second digital channel [68.2] many of the problems were cleared up. I have watched many of the Fox HD programs without a problem. But... the problem has returned and was horrible on Monday night during the House episode.

According to Quantum19 at WSYT the problem exists at numerous Fox stations around the country because many of them use similar equipment. Hence, many of them have a same problems. There is a thread over at AVS Forum that discussed this very issue.
http://www.avsforum.com/avs-vb/showthread.php?t=334413

[TomCat]

TC,

I have not noticed this on the LIL feed I receive from KTVU in the SF area. I just went back and checked a couple of things I recorded this week, and there is no freeze or mute going in or out of the local breaks. Now before you ask, yes, for reasons I won't state publicly, I do know that these were the local breaks I was looking at. ;)

The only problem I see on KTVU is that their splicer TIMING is way off. By that I mean, the splicer configuration can be adjusted so that the local and network streams are coincident, thus at least giving you a fighting chance of having the "switch" occur in the right spot (though as you said, the switch point is "elastic," so there's always going to be a +/- error). However, theirs is off by at least a second or more every time -- you will often see a segment start in SD for a second, then start again (repeating that same second) in HD.

Now, that said, watching several FOX stations OTA with various tuners, I have noticed that some of them tend to hiccup at the splice point. I used to have one that would mute about a second BEFORE the spice happened -- could always tell when the local break was coming. So, perhaps in your area, DirecTV is using an off-air receiver that is having a similar problem when it encounters the splice, and that upsets everything else down the chain? One thing that I know can cause problems is if the local station doesn't send 5.1 during local, or if the bit rate is different from the network.
That can cause a disturbance at the splice, which may or may not upset things.

Hope this helps!Thanks, VJ, and I have known you long enough to know exactly what your ;) reasons are. So for reasons I won't state, I can tell you the local station has done everything they can think of so far to remedy this, including mirroring the GOP structure and audio bit rate to make the splicer transitions as seamless as possible. Since FOX uses statmux on their feeds, there is no way to match the video rate to the local bit rate. But if they were mismatched far enough, that would cause buffer underflow/overflow enough to cause an actual video breakup on OTA, which it does not.

The splicer can either drop or add frames, so the timing between SD and HD going into a local break can differ up to 10 frames or so from the timing coming back out of that break. When the return switch from upconverted SD to HD happens is not determined by the splicer or a setting regarding that, but is a function of the offset for the automation relative event timing, which can be adjusted. The problem is that it is a moving target due to the elasticity in the splicer, so is not a hard target and occasionally the switch to HD will be late, and a few frames of network in SD will be seen. It's ugly, but so far there is no real fix for that. That problem is not specific to DTV, and can be seen OTA, but it is handled better by some tuners than others.

Non-synchronous splicing does seem to be at the root of the freeze/burp problem on DTV, as well. The splicer has the uneasy task of trying to compensate for two non-synchronous GOPs, both truncated, on the fly. On tuners that tolerate it gracefully there still may be a brief audio mute, and part of the GOP compensation may be to drop or repeat frames. The result is never perfect, but is usually tolerable. The DTV post-processing seems to have aggravated things, and that is why I am curious if this is happening in other markets.

You are correct about the audio bit rate and 5.1, but about the worst that this could cause would be a brief audio mute at the STB as the local decoder changes the downmix from 2.0 to 5.1 or changes gears to adjust to the new bit rate. It should not cause the severe disturbance seen on DTV boxes. But something does.

[videojanitor]

The splicer can either drop or add frames, so the timing between SD and HD going into a local break can differ up to 10 frames or so from the timing coming back out of that break. When the return switch from upconverted SD to HD happens is not determined by the splicer or a setting regarding that, but is a function of the offset for the automation relative event timing, which can be adjusted.

Well really, the switch timing TO the break is not controlled by the splicer either, and by that I mean, the time to make the switch is determined by the local station, either by entering the clock time into an automation playlist, or rolling the local break manually. This "time" is just when the contact closure will occur give the command to splice -- after that, you've got the +/- 10 or so frames that will happen in the splicer itself.

There is a config file in the splicer that Grass Valley can alter to adjust the timing of the streams so you are centered in the +/- window. I spent an enter week with them about a year ago trying to get ours exactly right. They were bumping it back and forth until I determined that the majority of the time, it was right on the money. We never, ever see any repeated video at the start of net segments (ie: no SD, then repeated in HD), and that's good!

Non-synchronous splicing does seem to be at the root of the freeze/burp problem on DTV, as well. The splicer has the uneasy task of trying to compensate for two non-synchronous GOPs, both truncated, on the fly. On tuners that tolerate it gracefully there still may be a brief audio mute, and part of the GOP compensation may be to drop or repeat frames. The result is never perfect, but is usually tolerable. The DTV post-processing seems to have aggravated things, and that is why I am curious if this is happening in other markets.

I would concur with that, even though I have evidence either way. It just sounds right! We recently ran into a situation where viewers with certain brands of cable DVRs had a problem when recording FOX from our station -- at every local break, it would make a new recording -- so for an hour show, it might be broken up into six or more pieces. No doubt this is all part of the same problem with these splices. Everything has to be "just so," and some boxes handle it better than others.

[kevinwmsn]

WALA Fox10 in Mobile,AL breaks up at the top of hour every hour. They are working on the issue too.