| Electronics > Beginners |
| Why does the average digital TV set take so long to "come on"? |
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| james_s:
I'm not sure if this is representative of the market as a whole, but most of the people I know want a TV that is just a large monitor with a simple UI and a bunch of HDMI inputs. Pretty much all bigger TVs these days have built in "smart" features but very few people actually make use of them, they're almost universally terrible. |
| CatalinaWOW:
--- Quote from: KD4PBS on April 13, 2018, 02:04:27 pm ---The CPU/controller and firmware in the TV for sure take quite some time to initialize, depending on the TV. And the channel change? Yes, the I-frame is part of the equation, but there are other things that affect this. We run all of our broadcast OTA channels with a variable GOP schema. For us, it might take as many as 45 frames until an I frame is sent, or it might happen every frame, all depending on how much motion exists in the video. I don't know how other broadcasters have their encoders configured, and there really is no "standard" on how many P and B frames before an I frame. The other factors are the PSIP table repeat rates. There are several that are sent, at different rates, and a few of them are essential to being able to put a picture on your screen, while the rest are not needed to display the picture. The most important table is the MGT (Master Guide Table). It's the table that describes all of the separate PIDs being sent in the program stream, including all of the other PSIP data. Without it, your TV doesn't know what to display. That's why we have ours set to repeat at 90 millisecond intervals. Next up would be the VCT (Virtual Channel Table). Again, the TV will likely not be able to display pictures until this table is received and processed. I've set ours to repeat every 395 milliseconds. These two tables are essential to displaying the pictures. As such, your TV has to wait until both have been received before making those pictures visible. I think the "standard" allows for slightly longer intervals for the MGT and VCT (I think 150ms and 400ms, respectively) So, a "channel flicker" will have to wait at least 400ms with most terrestrial broadcast stations before it's displayed. --- End quote --- All this goes a long ways toward explaining a phenomena on my system. Periodically when changing channels the set will get confused, go dark and eventually come up with a resolution not supported message. The frequency of occurrence is very heavily dependent on the channel. Unfortunately one of the worst is the local news channel which we frequently go to. Presumably the local channel has much lower refresh rates on these various elements of the transmission, and the set has more opportunity to get confused or have a noise event. |
| SeanB:
Your news channel likely has been allocated a very low bitrate in the multiplex it is using, meaning the data rate is very low, plus they have a very long I frame interval as the typical content is low motion. Thus the long time to both decode the channel out of the stream and then get a valid frame to start the video from, plus it likely is a multiplex that is transmitted at lower power so has a higher error rate to contend with for initial acquisition in the first place. Likely a bit of work on the antenna ensuring the signal strength is both high enough, and that all connections are well made ( basically undo every F connector, clean the core and apply a bit of contact cleaner, then tighten them up again, and replace any premade leads that are made from the nastiest grade of cheap almost screened cable) and there is a good error free signal into the tuner should improve things a lot. |
| SL4P:
With MJPEG, MPEG1 & MPEG2 streams of past, the streaming GOP structure was typically less than 2 seconds (I,B,P frames), but the newer codecs H.26x use much longer encoding structures, hence the 3-4-5 second wait for the next I-frame (full ‘Intracoded’ frame) equivalent. The bandwidth efficiency goes up, but the quality for a given (spatial and temporal) resolution and frame rate drops significantly. Money talk$. |
| CatalinaWOW:
--- Quote from: SeanB on April 14, 2018, 04:15:20 am ---Your news channel likely has been allocated a very low bitrate in the multiplex it is using, meaning the data rate is very low, plus they have a very long I frame interval as the typical content is low motion. Thus the long time to both decode the channel out of the stream and then get a valid frame to start the video from, plus it likely is a multiplex that is transmitted at lower power so has a higher error rate to contend with for initial acquisition in the first place. Likely a bit of work on the antenna ensuring the signal strength is both high enough, and that all connections are well made ( basically undo every F connector, clean the core and apply a bit of contact cleaner, then tighten them up again, and replace any premade leads that are made from the nastiest grade of cheap almost screened cable) and there is a good error free signal into the tuner should improve things a lot. --- End quote --- Generally good advice on improving the situation, but this comes in through the satellite, and short, clean signal paths on my end. The local news is a small town operation and the many signs of low budget in the production tell me that the signal problems were inserted before it ever got to the satellite provider. Or the satellite provider is providing some "payback" for the rather contentious rate negotiations that go on between the local guys and the satellite guys periodically. |
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