Why does the average digital TV set take so long to "come on"? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: April 12, 2018, 06:41:16 pm
content: It's probably a naieve question, but it's something I have long idly mused over. Why does a typical low end all semiconductor digital flat screen domestic TV take so long to emit a picture and sound after turn on, or after a channel change? Even the audio is slow to lock to a new channel, but my SDR radio receivers change instantly. Thanks, make me look an idiot....

author: bitwelder
author_rank: Super Contributor
timestamp: April 12, 2018, 07:09:23 pm
content: At least for slowness with channel changes, I remember rumours claiming it was to discourage 'zapping' channels (as in, changing channels during commercial breaks).It seems plausible but I don't know if it's true.

author: MosherIV
author_rank: Super Contributor
timestamp: April 12, 2018, 07:16:55 pm
content: I do not know exactly.My guess is that due to the streaming nature of digital tv, the decoder needs enough of the stream to reconstruct a whole frame or screen.I seem to remember that mpeg worked by encoding a picture every so many frames. In between these whole frames, only the difference is encoded.Maybe cheap decoders cannot give a picture until the whole frame.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 12, 2018, 07:42:16 pm
content: Because all software is awful, and everything is a computer.Boot-up is literally booting up; it may not be a general purpose computer as such, but it's something programmable, at least at manufacture time (but, following the premise that all software is awful -- they may release with bugs and provide future firmware updates through some mechanism). You'd have to check and see what TVs have been hacked/jailbreak'd, if this is useful at all or whatever.As for operating delays, yeah, there's quite a long delay, a second or so of video sitting in the decode buffer. It also can't show a picture until a keyframe has been received, which is transmitted every second or so (I forget what exactly, I don't care too much about DTV). Until then, only deltas are transmitted -- which is how you get those wonderful image corruption warps where a keyframe is lost and faces melt into freakish gibberish.There may be additional delay due to video buffering. A lot of TVs do that, which makes them particularly unpleasant for real-time applications -- computers, video games, etc.Tim

author: Gyro
author_rank: Super Contributor
timestamp: April 12, 2018, 07:44:30 pm
content: When I was designing (the hardware of) DTVs and Set Top Boxes back around the turn of Millennium, the pressure from distributors was always to speed up the channel change. Every millisecond shaved off counted in terms of user experience. Channel zapping is essential, especially with Satellite receivers with several hundred FTA channels, even when favorites are set up, there's no attempt to hinder it (maybe there is on some broadcaster specific boxes, I don't know).Yes, a large element of the channel change time is being able to start with a clean image, which needs an I-frame rather than the intervening motion interpolation P-frame and B-frames, that can take varying times depending on the channel quality. The last thing you want to start with is a green-screen of corrupt, slowly forming, picture. The other time element is pulling the programme information from the stream to put up on the channel banner in the UI. The stream has multiple channels encoded, with audio, video, and data packets interleaved, not necessarily in presentation order (hence the buffering).In terms or turn-on time, apart from the general initialization and housekeeping functions, the major time elements are putting up the Splash screen, if enabled, and more time consuming, updating the EPG (programme guide) data. Edit: A lot of sets check for s/w updates too.Edit: These days I assume there is a fair amount of time taken up booting Linux, Android or whatever too.

author: Rick Law
author_rank: Super Contributor
timestamp: April 12, 2018, 08:45:04 pm
content: Quote from: T3sl4co1l on April 12, 2018, 07:42:16 pmAnd those darn things has all the disadvantage of one too.- Randomly goes into bewilderment mode (everything seem to take 5x as long)- Hangs like any computer- Spies on youPretty soon, your TV will tell you: "The channel you are watching is prone to fake news and is considered 'unsafe for the community'; Please choose another channel now or I will automatically change your channel in 5 seconds."

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 12, 2018, 09:51:31 pm
content: Quote from: Gyro on April 12, 2018, 07:44:30 pmOh and, another factor is the time to negotiate the connection -- for cable. Cable boxes these days are little more than special-purpose network streaming boxes. AFAIK, network TV is always on (or, the most popular channels are), but the less common channels, and on-demand streams, are just that. Also part of the reason why cable modems have crap upload -- hardly any is needed in the first place.(It should be even less surprise, then, why telecom/cable companies want to control the distribution and pricing of content available on the general internet.)Tim

author: EEVblog
author_rank: Unknown
timestamp: April 12, 2018, 09:59:19 pm
content: Quote from: T3sl4co1l on April 12, 2018, 07:42:16 pmThis.My Sony smart TV's take a while to switch on, and then even longer until again the Netflix button works.So they deliberately try to make it display something first, but it still takes time for other function to load and start working.

author: james_s
author_rank: Super Contributor
timestamp: April 12, 2018, 10:04:28 pm
content: At one of my jobs we made digital video products and getting fast channel changes was something we put a lot of effort into with only modest success. It annoys the heck out of me too but it's just a consequence of the way digital broadcast works. There is also some significant truth to the comment above.It doesn't bother me as much as it used to though simply because there's nothing on TV worth watching anymore. Most of it is garbage to begin with, then everything is polluted with those stupid logos superimposed on top of the picture, and scrolling animated ads, and the overall ad load has been steadily increasing. Some broadcasters even speed up shows a few percent and/or edit out bits to pack in another commercial or two. I gave up TV entirely quite a while ago and stream everything. I was using a lot of DVDs but more recently I ripped all of my content onto a server and use Plex, I don't miss broadcast TV in the slightest. If I could go back to 1970s-80s analog TV and the quality content I would gladly do so.

author: rdl
author_rank: Super Contributor
timestamp: April 13, 2018, 01:08:15 am
content: Quote from: james_s on April 12, 2018, 10:04:28 pmI also think 70s - 90s TV was pretty good, but maybe I'm remembering through rose colored glasses. It's true though that at one time when you watched a program, that was all you saw other than commercial breaks. No logos, overlays, etc. to pollute the viewing experience. It seemed to start going down hill in the late nineties. Other than bits and pieces of a few Superbowls, I haven't watched broadcast OTA TV since 2008. I imagine it has gotten pretty bad since.

author: rdl
author_rank: Super Contributor
timestamp: April 13, 2018, 01:11:35 am
content: My TV is three years old now. It takes about 30 seconds to boot, after that all it does is display whatever is coming out the computer's video card. It has never had an antenna or cable attached. I don't even know if those parts actually work.

author: BradC
author_rank: Super Contributor
timestamp: April 13, 2018, 01:24:23 am
content: Quote from: rdl on April 13, 2018, 01:11:35 amThat is one of the tests the wife and I do when we go shopping for a new screen. "Can you turn it off and back on again please?". We have an LG that takes about 7 seconds and a Samsung that takes ~5. Had to sort through a load of chaff before we found units that ticked all the "requirements" boxes and had a minimal boot up time. Neither of those take any longer than my old CRT used to take to warm up.As others have said though, on channel changes you are at the mercy of the I frame. Same as CCTV. "Why does it take up to 2 seconds when I pull up that camera? It used to be instant".

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 01:45:44 am
content: Quote from: rdl on April 13, 2018, 01:08:15 amWell the fact that I have loads of 60s-90s TV content on hand confirms that there was plenty of good content back then, before the "reality" cancer took over every channel. It's the logo overlays that really ruined it for me though, I remember being annoyed at it when a few channels started showing logos for a bit after commercials, then at some point that cancer spread to *every* channel and they're displayed *constantly* which makes the content absolutely unwatchable to me. It's like a blob of something on the screen that I can't clean off. Then the ones that are solid colored, animated, or things that make sounds, wtf are network executives smoking? Then they act surprised that viewers are fleeing in droves. I can buy a series on DVD and watch it whenever I want, free of logos and commercials. The younger generation now has an expectation to watch what they want, when they want, and know little else.

author: Teledog
author_rank: Regular Contributor
timestamp: April 13, 2018, 01:54:26 am
content: The TVs for the last X years have been "Green" & energy efficient, etc. etc.Mandated by the government (along with RoHS built in obsolescence, but that's another topic)The old "instant on" were always drawing power, which thepowers that bedo not care for.My opinion?If I'm paying $$ for my power/water/resources, then the decision should be left up to me?But again, 98% of people have no clue as to how their appliances/automobiles/toilet/etc. operate..so, ..legislation is typically mandated down to the least common denominator/end politico rant

author: Bud
author_rank: Super Contributor
timestamp: April 13, 2018, 02:10:09 am
content: Netflix app takes about 30 sec to load. Makes me

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 07:33:30 am
content: Quote from: Teledog on April 13, 2018, 01:54:26 amThe "Instant On" you refer to kept the filaments in the vacuum tubes heated all the time, obviously consuming quite a bit of power. On the plus side they were great for cats, which had a tendency to sleep on the always warm TV console. I don't know how much energy regulations affect TV boot times now, I suspect if the CPU kept running all the time it would get in a bad state and need rebooting eventually anyway.

author: HT1950
author_rank: Newbie
timestamp: April 13, 2018, 08:28:57 am
content: The TV warming up so slowly is one (very annoying) thing, but why the screen goes off and on while the soundbar starts working? I have a soundbar connected to the TV, bothswitch on at the same tim, but soundbar needs even more time and because of it it looks like the TV needs to warm up two times... So the whole operation takes at least 15 seconds. Do you know why?

author: KD4PBS
author_rank: Contributor
timestamp: April 13, 2018, 02:04:27 pm
content: 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.

author: grifftech
author_rank: Frequent Contributor
timestamp: April 13, 2018, 02:15:46 pm
content: CCFL backlight warmup?

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 04:58:25 pm
content: Quote from: HT1950 on April 13, 2018, 08:28:57 amThat's largely down to the HDCP (useless copy protection) the sound bar picks the audio off the HDMI I'm guessing so it has to negotiate with the source and provide the decryption keys, then the TV has to negotiate with it and provide its decryption keys, then if you get lucky everything actually works and you get video and audio.Of course HDCP was cracked years ago so it's completely worthless as copy protection but that doesn't stop it from being mandatory.

author: rdl
author_rank: Super Contributor
timestamp: April 13, 2018, 06:25:51 pm
content: I paid attention the next time I turned the TV on and it actually took only about 10 seconds. The backlight came on at about 7 seconds, followed by the input selection display. The Windows desktop appeared maybe a second later. That doesn't seem too bad. I don't have any channels to switch, so I don't know about that.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: April 13, 2018, 08:45:18 pm
content: Man,We are so impatient these days! Does anyone recall old analogue valve TV's. Not only did they take an age to warm up, but in the UK at least, there were only a couple of channels until 1964 when BBC2 commenced. Much of the entertainment was trying to decide when, on switch off, the last 'spot' on the phosphorescent screen decayed into invisibility.Dave

author: IconicPCB
author_rank: Super Contributor
timestamp: April 13, 2018, 10:21:20 pm
content: You should have seen my old girlfriend... an analogue model... took for ever to "come on".

author: Bicurico
author_rank: Super Contributor
timestamp: April 13, 2018, 11:02:49 pm
content: A modern LCD TV is built with many components.And it behaves like a computer:1) When turned on, a bootloader inside the flash is started.2) The bootloader checks if all components are OK.3) The bootloader then needs to move the remaining firmware from flash to memory.4) Then the firmware starts, which is actually almost an OS - on Smart TV's.5) The firmware needs to start tuner, MPEG2/4 engine, video processor, audio processor, surround processor, etc.6) Meanwhile it starts showing the picture of the last set input.7) The video/audio stream needs to be buffered and gets sent to the video/audio processors for all sorts of enhancementsFinally the OS has finished booting and loading all the SmartTV stuff.9) The front processor is now ready to receive commands from the remote.10) If the DVB-S/S2/C/T channel is witched, the MPEG decoder needs to wait for a key-frame, which can take up to one second.This is just a rough list of all that is going on inside a modern TV!Better TV's may have some advanced logic to allow fast switching on channels of the same transponder, by keeping a simultanous tack of each stream.But if you change transponder, you will have to wait again for the tuner to lock in and the key-frame to appear.Regards,Vitor

author: coppice
author_rank: Super Contributor
timestamp: April 13, 2018, 11:48:56 pm
content: Quote from: Bicurico on April 13, 2018, 11:02:49 pmA modern TV is not just like a computer. It is a computer, and a perfectly good development system for its own code. In the TV development labs I've been to, people just connect a USB keyboard and mouse to a TV, and sit in from of its 65" panel developing the TV's code.

author: james_s
author_rank: Super Contributor
timestamp: April 14, 2018, 02:47:20 am
content: 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.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 14, 2018, 03:30:01 am
content: Quote from: KD4PBS on April 13, 2018, 02:04:27 pmAll 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.

author: SeanB
author_rank: Super Contributor
timestamp: April 14, 2018, 04:15:20 am
content: 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.

author: SL4P
author_rank: Super Contributor
timestamp: April 14, 2018, 04:44:07 am
content: 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$.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 15, 2018, 02:13:29 am
content: Quote from: SeanB on April 14, 2018, 04:15:20 amGenerally 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.

author: paulca
author_rank: Super Contributor
timestamp: April 15, 2018, 06:31:32 pm
content: Switching channel delay is due to buffering. The TV wants to get WELL ahead in the stream, like several seconds ahead so it can drop corrupt packets. If it cannot decode an audio or video packet it has to drop the correct length of both audio and video streams to keep the audio in sync. Even with a perfect signal all it takes is someone to switch on the oven or hoover and it will glitch. There is error correction built into the DVB stream but it has it's limits.Trust me, you want this. If you ever get a raw DVB card when it plays a corrupt audio packet it "chirps" really loudly, when it plays a corrupt video packet the screen goes nuts, when it doesn't resync the A and V streams the lip sync gets out of phase. When it runs out of buffer (or has none) then it freezes and stutters from time to time.If the later happens anyway, and it does, use "Live pause" if you have it available to create a new buffer of a few seconds.As to it taking ages to come on, probably because most of the TVs are just a custom built computer with a CPU and DSP which has a boot up time, possibly a warm up time on the analogue receiver and then buffering time for the selected channel.

author: bson
author_rank: Unknown
timestamp: April 16, 2018, 12:27:02 am
content: Quote from: coppice on April 13, 2018, 11:48:56 pmI've never seen that, but I have worked many times with Broadcom's reference boxes to create firmware for TVs, Blu-Ray players, and whatnot. (And grown to completely hate MIPS in the process.) Since these run Linux (usually very much the BCM stock BSP system and toolchains) it's convenient to tftpboot them from a cross build on the computer you work on when doing anything kernel or system related. For app development they all these days have environments like Air/Flash Lite with tricks like running off a USB stick or a CIFS mount.

author: bson
author_rank: Unknown
timestamp: April 16, 2018, 01:03:44 am
content: Audio always leads video, so in an MTS stream the audio you receive right now correlates with future video. This is to maintain lip sync; it's much cheaper and easier buffer and delay audio than video, then sync it to the video playback. This means when you first start demuxing MTS you get video for which you don't yet have audio. This delay also permits all kinds of audio processing, like surround sound and room equalization. This means if the video lags the audio in the muxed MTS stream by 1 second there's at least a 1 second playback delay, plus whatever lag the video decode and playback pipeline introduces. Obviously you also might suffer from large GOP sizes.Video processors also add lag when doing cadence corrections, cadence changes, and hide bad splices that introduce cadence errors. (This also ties into quality deinterlacing since apart from a slight stutter a cadence error can introduce field flips, where you get two odd/even fields in a row, which need to be detected and avoided as it causes horrible artifacting.)

author: ez24
author_rank: Super Contributor
timestamp: April 17, 2018, 12:45:53 am
content: I have a Hisense and the problem is it takes too long to turn off. I have to turn it off two times and there is about a 15 second delay between each turn off. It comes back on when I turn it off the first time.

author: Chris Wilson
author_rank: Super Contributor
timestamp: April 23, 2018, 11:59:00 am
content: I never though my post would creates as many replies, seems I am expecting too much and the old analogue sets, once warmed up were superior in instant channel lockingI still run two proper CRT analogue sets with digital converters, much to my wife's disgust who gets sniffy about having "ancient old tat" about the place. She won't want to her watch her soaps on one of mine then, when her SMPS caps in her mega screen beast let go....Thanks for all the fascinating info!