Why do you feel that iptv of telecom is not as clear as broadcasting?

I have been engaged in IPTV for several years, and I also know something about IPTV and digital transmission of radio and television. Let me correct the mistakes of many nonsense sentences first.

First, the State Administration of Radio, Film and Television (SARFT) is more of an administrative organization that manages TV and video services. The so-called statement that radio and television reduce the number of frames of code streams for operators is completely the heart of villains. In fact, both cable TV users and IPTV users are the same to SARFT. IPTV itself is also controlled by radio and television, so don't add it blindly.

Second, the TV transmission system of radio and television network is frequency division system, which is equivalent to transmitting all TV programs to TV. Whether you watch this channel or not, the TV signal is actually there. And IPTV multicast is equivalent to which channel you watch, which channel the server pushes to you. The selection of channel is equivalent to the selection of code stream, which saves transmission bandwidth. Moreover, the channel switching speed is extremely fast, which is difficult for human eyes to distinguish. There is no question of which channel bandwidth this channel grabs. Third, the transmission bandwidth of operators (only mobile, China Unicom and telecommunications are mentioned here, and other TV boxes dare not compliment) is enough to ensure the bandwidth of IPTV. To be sure, fiber-optic broadband has developed for so many years, and the transmission resources are already sufficient.

So why do some people say that IPTV is not as clear as HDTV?

There are three reasons for the fluency of any application: source server, intermediate transmission and client. Then the problem is coming. The following reasons may be that your TV definition is not as high as others' HDTV.

Has the IPTV provider improved the HD channel and HD film source? This point must be clear first. It is meaningless to compare ordinary channels with high-definition channels. If the operator provides you with HDTV service, you must have enough bandwidth, otherwise he will find trouble for himself. Does your set-top box support HDTV? Is the set-top box connected to the HDMI interface of the TV through a cable? Does your TV support HDTV? Is the cable quality between the set-top box and HDTV qualified? At present, transcoding of high-definition video may cause a little bit of coding loss, but it is unrealistic to say that it can be seen by naked eyes. IPTV technology has developed for so many years, and its maturity has been quite high.

In short, if you think the definition of IPTV is very clear and smooth, such as other people's HDTV, you should first ask the operator if you have provided HDTV service, and then see if your set-top box is connected to the HDMI port of the TV, and then make a comparison. In addition, the quality of TV itself is also very important, which we should understand.

Why do you feel that IPTV of telecom is not as clear as broadcasting? From some personal experience, this is more likely to be an illusion.

Although I am not a telecom IPTV user, I have used Unicom's IPTV service for more than three years, and I also have a cable network of radio and television at home. I don't think IPTV is as clear as radio and television. So, what makes users feel that IPTV content is not as clear as radio and television? There are several possibilities.

The film source itself is not clear enough.

From a technical point of view, the IPTV service of telecom or Unicom is the same as the cable TV network of radio and television, but the transmission mode is different. The IPTV service of operators is basically multicast, and the cable TV of radio and television is frequency division. More importantly, IPTV content also comes from radio and television.

The content produced in the last five years is basically high-definition content with resolution of 720P and above. Ten years ago, the highest definition of the content was only 480P p, so if the definition of the film source itself is not high, the effect is not clear whether IPTV or broadcasting.

The connection cable between the TV and the set-top box is different.

The IPTV box of telecom and the set-top box of radio and television should be connected to the TV through cables. At present, the cables connecting the set-top box and the TV are mostly HDMI, but in some areas, IPTV boxes provide traditional AV cables.

AV line transmits analog signals, and the highest resolution only supports 480P, while the resolution supported by HDMI line can be as high as 1080P. Some high-level HDMI cables support 2K resolution. Therefore, if the IPTV set-top box is connected with the traditional AV cable and the broadcast TV set-top box is connected with the HDMI cable, the definition will definitely be different.

In addition, in some areas, telecom operators, IPTV services do not adopt multicast mode, but share bandwidth with broadband * * *, so in the case of network card, the clarity of content may not be as good as that of radio and television.

When friends use the radio and television set-top box, they will find that the radio and television box watches TV clearly and stably, and there will be almost no jam. When you use telecom IPTV, you will find that watching TV sometimes loads slowly, so you will get stuck after watching it for a while, and then you will get stuck after watching it for a while. Why is the IPTV of telecom not as clear as that of radio and television? This answer is explained from the transmission network of the two.

I. Bandwidth allocation of transmission network

We compare the transmission network to a road. There will be many lanes on this road, such as motor vehicles and non-motor vehicles. Cars, trucks, etc. You can only take motor vehicle lanes, while electric vehicles and bicycles can only take non-motor vehicle lanes.

1, used for radio and television.

There are many lanes on this road, including dozens and hundreds. Each lane will be assigned to the designated program according to the prior agreement, which means that each program has one lane. For example, if the first lane is assigned to program A, then programs B and C can't grab the first lane. The second lane is assigned to program B, so programs A and C can't grab the second lane, and so on. The advantage of this is that each program is transmitted in its own lane, which is very stable.

2. For telecom operators.

There may not be so many lanes on this road, and every program will grab the lane. For example, program A grabs the first lane, so program B can't grab it for the time being. But once the A program is lost, it is very likely that the B program will immediately seize the first channel, so the next time the A program is transmitted, it is necessary to find another channel. Once the driveway is full, poor A-series programs will be transmitted aimlessly.

So in the evening rush hour, you will find that the TV set-top box is still so clear, but the IPTV of telecom operators may load slowly and get stuck.

Second, the quality of the transmission network.

We still compare the transmission network to the road above. If this road is of good quality, cars can run smoothly on it. If the road is bumpy, the car will bump. Do you feel good?

1, used for radio and television.

The indicators of radio and television transmission network are generally good, and all programs are transmitted smoothly. Although there will be some loss in the transmission process, it can be corrected quickly through remedial measures.

2. For telecom operators.

The transmission network is hard to say. Maybe it's blocked here, and the route there is broken. In order to solve these problems, QOS technology came into being, that is, the quality of service guarantee of transmission.

First, let's talk about the cable TV system and see how it transmits TV programs:

HDTV programs in China adopt the standard of19201080,50i. The sampling rate of video signal is 4:2:2. After sampling 10 bit quantization, the bit rate after quantization reaches 1.48Gbps, which is huge. Television theory tells us that there are a lot of redundant information in TV images, such as visual redundancy, spatial redundancy and structural redundancy. For example, because TV images are moving images, 25 images are transmitted every second. By comparing two adjacent images, we can find that there is almost no difference between the two images, so when we store the previous image, the next image only needs to store different parts of the two images, and this same part is redundant information. Therefore, in practical application, we need to get rid of these useless redundant information, which has no influence on our viewing effect. In this way, we can compress the original information again, and the bit rate after compression is 100Mbps, so the original high bit rate of 1.48Gpbs becomes a low bit rate. Although the bit rate becomes lower, there is no loss of image quality for human eyes. The next thing to do is modulation. Different from the Internet transmission mode (packet transmission), CATV adopts QAM (Quadrature Amplitude Modulation) and then sends it to the channel (cable or optical fiber), and the signal is transmitted to the user. After the set-top box is demodulated, our digital TV signal is restored. What you see is a very clear TV image.

Let's talk about IP TV first, which is very different from cable TV. What is the difference? As the name implies, it is spread through the Internet. In this case, it must conform to the transmission rules of the Internet (meet the requirements of various protocols) during transmission. At present, it is difficult to transmit the image information of 100Mbps, so it must be compressed before transmission. When the bit rate drops below 30Mbps, the human eye can obviously feel the quality of the image. At present, Internet companies can't give you 100Mbps bandwidth to transmit TV exclusively, and even the minimum requirement of 30Mbps is difficult to meet, so IPTV can't be clearer than cable TV. Because the Internet uses packet interaction technology and adopts the store-and-forward mode, when a packet arrives at the switch, it must be stored in the cache first, and then the next packet is taken out of the cache and forwarded from the corresponding port of the switch after the previous packet has interacted, which means that IPTV will cause great delay, and there is another key problem. When the Internet transmits video image signals, it uses UDP links. It is a connectionless transmission mode, so the data transmission is unreliable and the error rate is high. In data cutting, it is necessary to add various header and trailer information to the original data packet, which also increases the network overhead and reduces the transmission efficiency. Because its transmission rate is far from the basic requirements of HDTV, its picture quality and definition are far less than cable TV, and there is a great delay.

IPTV and DVB of telecom operators have different video sources and different bit rates. IPTV video comes from IPTV operation license company under Radio and Television Group, and operates in cooperation with telecom operator (China Telecom Mobile Unicom). DVB, on the other hand, is operated independently by the radio and television company under the Radio and Television Group. There are two different teams on both sides. And which code rate is better, the situation varies from place to place, not absolute.

The policy of Radio and Television Group is to let the two coexist, but the operation methods are different. At present, IPTV, such as CCTV 3568, which limits the natural advantages of the network to a certain extent, is not allowed to broadcast live on IPTV in principle (the actual situation will be biased, for example, the incident of radio and television suing telecom operators for secretly broadcasting the CCTV5 World Cup in the 20 18 World Cup has caused heated discussion).

There are two kinds of IPTV licenses. The license of telecom operators is IPTV transmission license, which is different from broadcasting and television. The broadcast control right of IPTV is still in radio and television, and telecom operators only participate in the sharing by providing broadband networks and user traffic.

As for a bunch of people who say that telecom operators have lowered the code of IPTV, this is nonsense. The following is divided into two aspects.

First of all, radio and television licensees stream multicast videos with different bit rates to telecom operators, and telecom operators provide multicast replication points on the network for users to access set-top boxes and obtain multicast streams to watch live channels. This is the IPTV live broadcast process. The bit rate of users watching live channels only depends on the channel selection of users in the set-top box and the bit stream provided by radio and television. Telecom operators only provide a network channel, and there is no transcoding process in the middle.

IPTV also has the functions of live channel time shift and TV review, which are unicast mode instead of multicast mode. The process is to transcode the multicast stream into a unicast stream, then video record the program and store it in pieces, and then feed back the file storage location information to the broadcast control platform (this transcoding recording and piece storage process may be completed by the on-demand platform of radio and television, or it may be completed by the content distribution platform built by operators, depending on the actual situation of cooperation between the two parties, but the broadcast control platform must belong to radio and television). If the user moves forward or chooses to watch the recorded program backward during the live broadcast, the set-top box will send a request to the broadcast control platform, and the broadcast control platform will reply the download address of the video file to the set-top box, and the set-top box will request to download the recorded video file with time stamp, and play it on the set-top box through the playback software and output it to the TV at the same time. The bit rate of this downloaded media file is definitely the same as that of the live multicast stream, and there is no need to reduce the bit rate. Otherwise, when you watch the live channel, you will see programs with different code rates. In fact, this is not the case under normal circumstances.

Lowering the bit rate does happen. This means that the IPTV set-top box detects that your network is in poor condition, the current high bit rate channels are often stuck, or your TV simply can't support high bit rate programs. The set-top box will automatically request to join the same channel low bit rate multicast to realize automatic code reduction and ensure that the program you want to watch can be played smoothly. This process has nothing to do with telecom operators.

Some people think that telecom operators will reduce the code privately, not to mention it is not good for telecom operators. The key point is that the IPTV license is issued by radio and television, and the overall operation of IPTV is also accepted and controlled by radio and television. Telecom operators simply don't have such great rights.

The white cable of radio and television home has a very large bandwidth, because of the large bandwidth, of course it is not stuck. In addition, the transmission mode is broadcast, and all users receive the same signal at the same time, which is not iptv point-to-point playback mode, and there is no pressure on the broadcasting equipment in the computer room.

Finally, talk about the bandwidth of the white line. The white wire is called coaxial cable, which can transmit analog RF signals. In the past, it was used to transmit TV. There are about 70 programs, and each TV set has an RF bandwidth of 8M. Now upgrading to digital TV, using 64qam modulation technology, the RF bandwidth per hz can be turned into 6-bit digital signals. According to the RF bandwidth of 750M, coaxial cable can transmit 4500mbit data signal, which is equivalent to the data rate of 4.5Gbit per second. Such a large bandwidth can transmit hundreds of sets of SD and dozens of sets of HD at the same time. In the future, only a few sets of HD can reduce the transmission of 4K.

I have the most say in this question. The fundamental reason lies in the quality of transcoding. My family has both IPTV and cable TV programs. The 300M fiber-optic broadband installed in July, the special 4K high-definition set-top box for telecom, Samsung 65-inch 4K high-definition TV and HDMI 2.0 connection are absolutely up to standard. Just during the World Cup, a comparison was made. Objectively speaking, the images of broadcast cable programs are clearer, and the details of IPTV programs are seriously lost. This is because the compression is too hard. Broadcast cable and IPTV are essentially so-called "digital TV", and both adopt H.264 compression mode. If the compression is too harsh, the details will be pasted together, and the two are only transmitted in different ways.

First, the source of cable TV programs of radio and television is source broadcasting, which is directly obtained from satellite sources (Zhongxing 6A and Zhongxing 6B), most of which are these two satellites. The film source of Phoenix Satellite TV is 105.5, and some foreign programs are from other satellite sources. Guangdong Cable also has TVB Emerald Satellite TV, which is optical fiber transmission! These program sources are all broadcast by source code, and there is no need for secondary transcoding! Some radio and television program sources in southern China are transmitted through their own optical fiber backbone network, with satellites as backup. Television program definition cable is better than IPTV!

Second, IPTV, whether it is telecom or other operators, is transmitted by transcoding and streaming media after its source, and needs to be compressed. You can tell by watching TV. The static picture may be clear, but it will be blurred or tailed when entering the dynamic picture. Although the network box is called 1080P Full HD and 4k HD, the standard of global radio and television is interlaced scanning, and the HD is 1080i. In addition, the network transmission has bandwidth limitation, so it is necessary to compress the code stream, which has a great impact on the image quality!

The advantage of IPTV over broadcasting cable lies in the choice of content. Besides live TV, there are other movies and TV works to watch. There is nothing to watch on radio and TV except watching live sports on cable TV. I also read more online. Because of the delay and image quality problems, unbelievers can record a video with a set-top box, compared with IPTV!

Don't spray it if it's not good, just ignore it. If you think it's good, just pay attention. Thank you! Welcome those who like to study this aspect, and communicate together!

Telecom iptv is indeed worse than radio and television in definition, probably to save bandwidth. I am a telecom user in Deyang, Sichuan. CCTV's Dolby HD channel actually only outputs two-channel audio signals in pm format. The TV box supports Dolby, and I have set the box to hdmi transmission. Only a few movies in VOD can output dolby digital 5. 1 channel audio signal. I remember that the standard audio signal of HDTV should be in dolby digital format, and the live broadcast of telecom TV obviously has a delay of10 for 30 seconds. However, the range of telecom TV transmission is relatively wide, and there is no extra charge, so it is still quite fragrant. Although radio and television are doing well, their broadband is poor. After all, the general situation now is that broadband is used more than TV. If I am not short of money in the future, I will install a telecom broadband and a radio and television HDTV, and the best of both worlds will not be entangled.

Radio and television still take the traditional coaxial line, and the other three major operators have long been optical fiber. Why is the clarity of IPTV not as good as that of radio and television? The root cause lies in the program source code.

Many people may not believe it. Most of the high-definition program sources are in LeTV's library. After the failure of LeTV, many apps lost the source of high-definition programs. After using other libraries, the clarity is greatly reduced.

Let me add here. Although LeTV can't do it, its program clarity, APP interface design and live broadcast level are still unsurpassed. In particular, PPTV, which has taken over most of the sports copyrights, can't really see the horror of live low.

Of course, the definition is not as good as that of radio and television, mainly in some live TV sources. If you watch these video website programs through an APP like iQiyi, the clarity is higher than that of radio and television.