WTMJ-DT and Statistical Multiplexing

[techboy]

Thank you Brian for your post.  That's the kind of information I'm looking for.  I FTP'd a short problem stream to MIT in Korea for analysis and they noted a high number of packet errors, but suggested that they should not be serious enough to cause a problem.  I also can play back a stream without break-up using the Elecard software Mpeg decoder.  TMJ only breaks up when using the MIT card: recorded or live.  ( TMJ also freezes my SONY HD STB in the same places the MIT card pixels. )  I've e-mailed K.A. ( the chief engineer ) at TMJ, so he is aware that I have a problem, but he hasn't heard complaints from anyone else.   Of course, almost everyone gets their HDTV from cable, and how would the average OTA guy recognise and report a problem back to the station engineer? (Rethoric.)  I personally believe there is a serious problem with the TMJ stream, but I don't have the equipment to prove it.  Maybe some hardware handles it OK, but I suspect there are many that don't.   I have TSR lite, but that is of little help.  What I need is a real time Tektronix system analyzer.    Have you e-mailed with Terry Petersen?  He is very interested in this "issue".  He is the intermediate link between Digital Connection and MIT in Korea.  He has been very helpful.  They are also seeing this on KQED in San Francisco.  I'm sure Terry would like to hear from other MDP users with this problem.   Are you linked with the AVS MDP user forum?

Tod

[Jaxxos]

I have also been experiencing this problem, it seems to pause for a moment then go again. I have it on SD and HD broadcasts OTA, but not on the satellite SD broadcast.

I have good signal strength 86%-90%, I am using a DishNetwork HD receiver 411, I don't know much technical information but it does say MPEG 4 on the front of the turner.

I have watched NBC before OTA with no problem I started to notice the problem somewhere after the last Apprentice series ended and after Nascar went back to NBC. I do not experience this problem with any other local OTA HD or SD broadcasts.

[Doug Mohr]

Thank you Brian for your post.  That's the kind of information I'm looking for.  I FTP'd a short problem stream to MIT in Korea for analysis and they noted a high number of packet errors, but suggested that they should not be serious enough to cause a problem.  I also can play back a stream without break-up using the Elecard software Mpeg decoder.  TMJ only breaks up when using the MIT card: recorded or live.  ( TMJ also freezes my SONY HD STB in the same places the MIT card pixels. )  I've e-mailed K.A. ( the chief engineer ) at TMJ, so he is aware that I have a problem, but he hasn't heard complaints from anyone else.   Of course, almost everyone gets their HDTV from cable, and how would the average OTA guy recognise and report a problem back to the station engineer? (Rethoric.)  I personally believe there is a serious problem with the TMJ stream, but I don't have the equipment to prove it.  Maybe some hardware handles it OK, but I suspect there are many that don't.   I have TSR lite, but that is of little help.  What I need is a real time Tektronix system analyzer.    Have you e-mailed with Terry Petersen?  He is very interested in this "issue".  He is the intermediate link between Digital Connection and MIT in Korea.  He has been very helpful.  They are also seeing this on KQED in San Francisco.  I'm sure Terry would like to hear from other MDP users with this problem.   Are you linked with the AVS MDP user forum?

Tod

Please PM me the contact info for WTMJ and I will file a problem report as well.

Doug

[tencom]

I recorded a half hour segment of a channel 4 HDTV production, and then checked the file, with a computer program called "MPEG REPAIR" which can be used to check transport streams for errors and it came up with  a total of 131 video frames that had errors most were either Macro block  and motion vector errors
It also showed a time stamp error of about 1 second this is more errors then any other channel that I checked plus 3 audio packets were in error I send this text file to the engineering department at the station and responding to my E-MAIL was " Kent Aschenbrenner", whose repliy was  "We are researching this issue".
So lets see what happens!

[techboy]

When I started this thread, I was narrowly interested in finding out if other users of MIT PC cards were experiencing the same problem that I was having with macro blocking and pixelation on WTMJ-DT since they added the WX sub channel.  As evidenced by this thread, many people are having reception issues with WTMJ's DT statistical multiplex program stream on many different receiver platforms.   I have it on my Sony STB and my PC card.   I am a former WTMJ TV engineer; retired about 3 years ago.  I consider myself to be quite technically competent on the issues.  I have been in contact with Mr. Aschenbrenner, the Engineer In Charge, at WTMJ TV.  He is well aware that a number of viewers are having reception issues.   His last response to me was that he is working with the vendor of the SM encoder to try to resolve the issue.  Statistical Multiplexing has been primarily a satellite delivery encoder method.  It is new to OTA TV.  The idea is to allocate "bandwidth" on an "instantanious as necessary" basis.  So, when there are multiple program streams,  when one stream needs  to carry more data, the secondary stream is reduced.  So, compression quotient is not constant.  Seems to work great for the guys at Direct TV.  But of course their receivers were designed for this.  

So for now, I think we need to wait and see if "the vendor" can provide a solution.  If not, then we need to let WTMJ know they will loose viewers and hope we can strongly encourage them to return to fixed multiplex streams.

I'd really like to know if this is a wide spread issue. What percentage of viewers are affected by this problem.  If I were to go to Flanner's and have them display WTMJ on all the sets in the showroom, how many sets would have the problem?  Is this an issue only with older 1st and 2nd generation gear?  Or does it affect a large number of viewers who simply don't recognise that the picture isn't supposed to break up frequently?  

So keep the feedback coming.  What's your experience?

Tod

[tencom]

Isn't VARIABLE BIT RATE, the samething? Also doesn't CATV  use STATISTICAL MULTIPLEXING for their digital output?

[techboy]

For those interested in the "details"....  Go to the Wikipedia and search the terms statistical multiplex, vriable bit rate, time division multiplex, etc., and follow through on the various links.  Prepare for an education......

[tencom]

Also the differences between the P and  I  and B video frames.  What the DCT function is also what is the purpose of the equalizer , plus what a trellis encoder does and many other ATSC fundamentals associated with this technolgy.

[bubbaridesfast]

Is this an issue only with older 1st and 2nd generation gear?  
Tod

Well, I have had my new D* H20 STB long enough now that it also does suffer the same problem although it the visual effect is slightly different but still happening.

My 2nd generation LG box would pixelate but on this one the video freezes temporarily.

[Will]

I have noticed this on 4-1 OTA also.  I have a Sony kd34xbr960 (widescreen tube with ATSC tuner) and 4-1 pixellates often.  It looks like white dots in the darker areas of the screen.  

Antenna strength shows 98%, and I have no problems like this on any other digital OTA stations.  I can't compare 4-1 OTA picture to cable -- I don't have cable or dish; only OTA.

Hope this helps.

[techboy]

Those little white dots you see on WTMJ-DT network shows are an entirely different problem.  If you don't see large square blocks or freezes, your equipment is not affected by the statistical multiplexing issue.  It would appear that some receivers are OK while others react adversely.

[Will]

Those little white dots you see on WTMJ-DT network shows are an entirely different problem.

Can you explain this to me?  Is this also a WTMJ-DT-only issue?  If so, are they aware of it / working on it / do they care?  Or is it just my TV?

Thanks!  (and sorry about the thread-jacking)

[tencom]

Apparently channel 4 DTV OTA Engineering staff sees nothing wrong with there Digital OTA signal,  as no improvement has been noticed, maybe the codec used in some decoders might have to be updated to accomidate "statistical multiplexing"
However if you have cable and have the ability to decode QAM 256 the problems with channel 4 OTA signal aren't present on the cable  signal as measured both by sight and using "mpeg/repair" to analyze both stream.                                        On the OTA signal
"mpeg/repair, error log, states that they are using "differential motion vectors"
and not all decoders can support DMV that maybe the problem. I can't find any data for DMV to say for sure if its just a problem because of buggy software being used by WTMJ-TV as I undertstand it DMV is only used when  B frames aren,t being used but in channel 4s case they are, so who Knows whats at fault,

[techboy]

WTMJ engineering has been working with Leitch and has recently made some changes to the SM parameters.  Finding test equipment and knowlegable personnel to track down this issue has been a problem for them.  So, an entire new SM encoder ( Same model, same manufacturer ( Leitch )) was put into service for testing.  I've noticed a small improvement on my system, but the problem continues.  It seems to come down to null packet over-runs.  Anyone else who's been followiing this thread notice any changes?
Tod

[waterhead]

My PC program (Media Portal) no longer crashes when I tune to 4.1, from another channel. I was having to exit live viewing, then select 4.1 when re-initializing the tuner. I guess that counts as an improvement.