How many seconds does it take for IPTV to change channels? One or two seconds is due to the mechanism, and more than ten seconds is due to illness. I measured the dividing line.

During the Spring Festival last year, I was watching TV at my father-in-law's house. He pressed up one channel after another on CCTV1. He pressed it once and waited for ten seconds, then pressed it again and waited for another ten seconds. After pressing the fifth time, he became impatient and threw the remote control on the sofa.: 「This TV gets dumber the more I use it. 」My first reaction was that the box was broken. Later I compared it with my own box and checked the watch, only to realize that it was not that simple.—— My box also has to wait to change the channel, but the wait is one or two seconds, while his wait is more than ten seconds. . The ten seconds difference in between was partly due to the mechanism that no one could avoid, and partly due to the fact that his box was really sick. This account must be settled separately. Otherwise, if you take a moment or two to report for repairs, the master will come to your door and test everything, everything is normal, and the trip will be in vain. ； It is unjust to hold it on for more than ten seconds without repairing.

Let’s talk about the normal part first: No one can escape these three stages of waiting, changing channels

My box also has to wait a second or two to change channels. This is not because the box is slow, but because of the rules of the IPTV streaming method. The moment you press the remote control, there is more going on behind the scenes than you imagine. It is broken down into three parts.

The first paragraph is Unsubscribe from old station . IPTV live broadcast uses multicast - the computer room sends dozens of channels out at the same time. Your box only "subscribes" to the channel you are watching, and does not occupy other people's channels. The first step in changing channels is to send an unsubscription message to the old station. The problem is that online equipment cannot be returned as soon as you tell it to be returned.: What if the remote control is pressed and accidentally touched? Therefore, there is a confirmation link in the agreement. The device must send a query once or twice to confirm that no one has read it before stopping the flow. This section alone would take a second or two at worst. This is to prevent your hands from slipping, not a malfunction.

The second paragraph is Join new station . Newspaper subscription requests for new stations start from your home box and are reported level by level. Each hop of equipment must be processed and takes time. It takes milliseconds to look at each station alone, but it takes a few tenths of a second to stack up. You can't do anything about this period inside or outside your home, it's the account within the operator's network.

The third paragraph is the most hidden and the biggest gimmick: Wait for keyframes . The video stream is not sent out one complete picture at a time - that would take up too much bandwidth. The real method is to send a complete frame (called a key frame in jargon) every half to one second, and the middle frame is all the difference of "where it moved compared to the previous one." This saves bandwidth, but the price is: You join a channel midway, and the difference you have saved in your hand does not have a reference picture. You cannot interpret the picture, and you can only wait for the next complete picture to arrive. . If you are lucky, you will wait for half a second after walking, but if you are unlucky, you will wait for a full second. In addition, the box needs to pre-read a little buffering and anti-shake, which adds up to one or two seconds. I am here The article on multicast principles I talked about this mechanism using the metaphor of newspaper subscription. What I’m talking about here is the time account.: Unsubscription confirmation, step-by-step joining, and key frame waiting are all paid for changing IPTV channels around the world. This is how one or two seconds are spent.

Check the watch for self-test: First, distinguish whether you are paying for the mechanism or for illness.

Now that you know the normal accounts, the next step is to determine who will be responsible for the extra waiting in your home. The way I taught my father-in-law was very crude.: Use your phone to check the watch, and change ten channels in a row. Pay attention to two things every time you change one.—— The speed at which the station number and logo pops up, and the speed at which the screen keeps up. .

Normal channel changing looks like this: The station number is played first, and the screen follows it every one or two seconds, all ten stations are played like this, the speed is even. This is the mechanism's money, don't mess with it, there is no point in reporting for repairs, the master can't repair the agreement. At that time, my mother-in-law felt that she had reported a problem by changing the channel and calling 10000 slowly. The master did a remote test and said "everything is normal", so the call was in vain.

Pathological change of channel is another kind of appearance, which needs to be recognized separately.: It takes several seconds for the station number to pop up. , indicating that it is stuck on the box's own interface and has nothing to do with streaming. ； The screen came out but it was blurry for the first few seconds. , the more obvious it becomes at night, it is the account on the signal side. ； The standard definition channel is smooth, and the dedicated 4K channel is half a day slow. , is the account on the decoding side. Each of these three diseases belongs to its own department, and they will be discussed one by one below.

The first disease: I can’t even flip through the channel list, it’s the box’s own fault

My father-in-law is like this. I went over to take a look and found that not only was it slow to change channels - when I pressed "Confirm" to bring up the channel list, the list itself took three to four seconds to pop up, and it took even longer to scroll through the on-demand column. The list page does not touch multicast at all. The fact that it is stuck like this shows that The problem is with the box itself and has nothing to do with the wiring. . Go into settings and scroll through the storage column. There are only more than 200 megabytes of available storage out of 8 gigabytes, which has been completely eaten up by two Landlords and the cache accumulated over the past few years. When the storage is full, the system chokes on everything.

This kind of practice is cleaning up, not reporting for repairs.: Uninstalling unused applications, clearing the cache, and deleting installation packages that have not been deleted after installation can usually lead to immediate results after completing the four steps. The article about the box getting stuck the more you use it I have written the complete steps, but there is also a big pitfall that you must know before factory restoration - the business authentication account, which I will not repeat here. After clearing and returning cards, I was stunned for a long time even when I pressed the remote control. That’s because the box is really old. By the way, a reminder: The IPTV box is the operator's asset and is rented to you. If you are too old to save it, you don't have to pay for it yourself. You have to report it to a repairman and have it replaced for free.

second disease: The screen was blurry for the first few seconds after it came out. It was on the signal side.

This kind is the best at pretending. After changing the channel, the background icon popped up and the picture came up. It was blurry and mosaic for the first few seconds, but it became clear after a few seconds. It looks like "Changing channels is slow", but it's actually Multicast packet loss ——The shipment arrived, but a few packages were lost on the way. The differentially encoded picture loses one packet, and the following series of differentials cannot be deciphered. I’ll give you a blurry look. ； If the packet loss is serious, the entire section will be stuck. This problem has nothing to do with the channel changing mechanism, it’s a matter of line margin.: If the light attenuation is close to the critical line, the entire PON port is crowded during the evening peak, or the network cable has eight cores and is slowing down, check them one by one first. The mosaic piece I have calculated the three accounts, and there is a judgment formula that is equally useful here.: Packet loss on the Internet is only slow but not blurry, and packet loss on live broadcasts is blurry. If the computer speed test is normal but the TV is blurry, it is probably due to multicasting and not broadband.

There is a simple way to help you divide the pot: Switch to several channels with different bit rates and watch each for a few seconds. The standard definition channel has a code stream of two to three megabits, and it can withstand any bad line. ； The HD channel has eight or nine megabits, and the 4K channel has twelve megabits and upwards. If there is not enough margin, it should be blurred first. If the SD header is blurry for a few seconds, it’s a real packet loss. ； Only high bit rate stations are blurred, indicating that the line margin is just stuck on the line. On the channel information page (press the "Confirm" or "Information" button on the remote control), you can see the bit rate of the current channel, and check it.

The third disease: The 4K channel is slow because the decoder is struggling.

This is the disease that my own family encountered, and it is the most unlikeable disease. My box's standard definition and high resolution channels change smoothly in one or two seconds. Once entering the 4K zone, I have to wait five or six seconds to change channels, and there is a pause in the first second when the screen comes out. At first, I thought the line was tight due to the high bit rate of the 4K channel, but the bit rate for viewing the channel information page was only 12 or 3 Mbps, so the line margin was sufficient. Later I figured it out: The 4K channel uses H.265 encoding, and the decoding burden is several steps heavier than the H.264 of the HD channel. . Older box chips do not have a 4K hard decoding unit and rely entirely on CPU soft decoding. It is difficult to start broadcasting - it is not that the network delivery is slow, but that the box decoding is slow. The new box with 4K hard decoding is almost as fast as the HD channel, and this is the difference in price.

How to tell which kind of box your home belongs to? The most direct move: Take the same 4K channel and compare the channels on the box and a new TV (or new box) that supports 4K. The new device is faster than the old device and it is basically a matter of decoding. There is no switch on the user side of this kind of patient, and there are only two roads.: Either accept it and watch less 4K channels. The source limit of HD channels is originally 1080P. The picture quality article I have said that I am optimistic that the difference between HD channels and 4K channels will not be that big in daily living room distances. ； Or call 10,000 and ask about changing to a 4K box - but first confirm whether the package includes 4K permissions. The box is one door, permissions are another door , without permission to change the box no matter how good it is, you can’t enter the 4K area. By the way, let’s talk about the other half of the reason why other people’s boxes change channels quickly.: The manufacturer has made optimizations such as pre-adding adjacent channels on the new box and unicast and fast streaming when changing channels. These are all done in the box and the computer room. There is no switch on the user side, and you can't set it up no matter how you use the old box.

ending: Use a table to sort out the accounts before deciding whether to take action

That night at my father-in-law's house, I taught him this set of self-tests for measuring watches, and he reached the conclusion after pressing them for ten minutes.: The channel numbers and logos of eight out of the ten channels pop up in seconds, and the picture catches up within a second or two. Only the two channel lists of satellite TV are high-definition. After clearing the storage, the list opened instantly, and he recognized the remaining one or two seconds of the screen waiting - I explained to him that this was the rule of "ordering newspapers", and he became more at ease.: Knowing which part is normal and the remaining part is wrong before taking action is better than anything else. The table is collected here:

There is also a related experience: My mother's version of the topic of slow channel changing is different - she confused the channel changing with the time shift, thinking that watching the channel change backwards was a box lag. In fact, they are two different things. Time shift is a function that automatically moves back by pressing the "Left" key. Looking back and time-shifting the article I have written here that changing channels will clear the time-shift progress, which is a rule and not a fault. If there are elderly people at home, it is enough to teach them to recognize whether the station number has popped up or not.: It is normal to wait while the station number is fast but the picture is slow. Only when the station number cannot be played can you call someone. This judgment is enough for my two elderly people to save at least three trips to pay for repairs.