If the TV cannot be found or there is no sound when casting the screen, 90% of the time you can fix it by yourself after three levels of troubleshooting.

In the evening, my wife cast the screen on her mobile phone to catch up on a TV show. She clicked on the small TV button and scrolled for a long time, but the device list was empty and she couldn't find anything. Her mobile phone signal is full, the internet speed is normal, and she can watch videos without any lag. I took it over and took a look and was very happy - the phone was connected to the neighbor's WiFi upstairs, and the name was exactly the same as my 2.4G. Her phone "remembered" the neighbor's network in the middle of the night and automatically connected to it.

There are many ways to overturn the screen projection thing, but after tossing around with the TVs, boxes, and speakers at home, I found that all the overturns were three-layer.: The failure to find the device is a matter of the discovery layer, the presence of images but no sound is a matter of the format layer, and the stuck PPT state is a matter of the transport layer. Through hierarchical inspection, 90% of the problems can be located within five minutes.

First figure out which way you are investing. Three ways are different things.

Many people think that screencasting means "sending the screen to the mobile phone." In fact, the screencasting button on the mobile phone does something different from what you think. I split it into three roads and said:

first road: The TV button in the online video app. Click on the small TV icon on the playback page of Tencent, iQiyi, and Bilibili to select the device. What it does is send the playback address to the TV, and then TV pulls itself . The mobile phone is just a remote control from beginning to end. After you put it on, you can lock the screen, exit the app, or even walk out of the house, and the TV will continue to play. Therefore, whether the screen projection is stuck on this road has nothing to do with the half cent of the mobile phone signal. It is a matter of the TV's own network.

second way: Mirror local files. Videos from the mobile phone album and movies from the NAS are pushed to the TV through DLNA. This way is to really push the video stream from the mobile phone or NAS to the TV, using the home WiFi and occupying the home bandwidth.

third way: Screen mirroring. Copy the entire mobile phone screen to the TV, which is useful for playing games and video conferencing. Most Android "wireless screencasting" uses Miracast, which is a direct point-to-point connection between the mobile phone and the TV, and does not occupy the bandwidth of the home router at all. ； Lebo's solutions, which are common on domestic TV, essentially record the screen on a mobile phone, add encoding and then push the stream. The mobile phone will get hot and the picture quality will be compromised.

first floor: No equipment found, five real culprits ranked by probability

The real murderer: The mobile phone and the TV are not on the same network. This is the most common occurrence, and that was the case in my house. Except for the case of accidentally connecting to the wrong network (I later changed the name of the WiFi at home, this matter is The article about changing the WiFi name (written in), there are two other: One is that the mobile phone is connected guest network ——My relatives came to stay for a few days. I turned on the guest WiFi and my wife’s mobile phone connected easily. The guest network was isolated from the main network by default. The devices could not see each other and the screencasting was naturally blinding. What the guest network can and cannot do I have tested it and found that it cannot be touched on NAS or screencasting. ； The other is that the TV is connected to the WiFi of the optical modem, and the mobile phone is connected to the WiFi of the router. The two network segments cannot find each other. Remember one thing: Under the same router, the mobile phone is connected to 5G and the TV is connected to 2.4G. Doesn’t count Cross-network, can discover each other - don't listen to the saying on the Internet that "screencasting must be connected to the same frequency band".

The real murderer two: AP isolation is on. There is a switch for "AP isolation" or "disable wireless user communication" in the background of the router. When it is turned on, even a WiFi device will not be able to see each other. This switch is normally off by default for home use, but I have seen it turned on on second-hand routers and routers installed by landlords. What is AP isolation and where are the switches of each brand? Wrote a complete walkthrough.

The third murderer: The reception program on the TV side is not in place. For Android TV to be used as a screen mirroring receiver, a corresponding App must be running. After upgrading the system of the old TV, or clearing the background of the "screencasting and receiving" app on the TV, it will no longer appear in the list. Look through the list of TV apps and install one if it’s not available.

The real murderer four: TV fake online. After the TV turns off the screen and goes into hibernation, the DLNA discovery service is disconnected, but sometimes its name is still cached in the mobile phone list. When clicking on it, there is no response or a connection failure is reported. First use the remote control to wake up the TV completely, wait for more than ten seconds before turning on the TV.

The real five: Multicast is blocked. Discovery protocols such as SSDP and mDNS that are used for screen casting use multicast. If the home network is divided into VLANs and finely isolated, multicast cannot pass through and it will not be discovered. Ordinary families cannot encounter this. Only those who have gone through soft routing partitions are suspicious. What's going on with multicast? Wrote the principles.

second floor: There is picture but no sound when uploading, the format is causing trouble.

This level is the most confusing, because the words "cast in" make people think that it is successful, but in the end, the characters in the TV series opened their mouths and fell silent. I'll put them in the order they've been stepped on:

DTS and AC3 audio tracks are not recognized by the TV. I transferred an old movie from the NAS to the TV. The picture was fine but there was no sound. The sound file itself was not damaged, but the TV refused to decode the audio track. This is not a fault of screencasting, it is just as dumb when played directly on the TV—— The TV plays the NAS movie directly I have written in detail about the solution to this pitfall, including changing a track or changing a player.

External subtitles are not included. DLNA streaming only pushes the video itself. The srt subtitles hanging next to the mobile phone will not follow, and it will be raw on the TV. Either press the subtitles into the video, or install a player on the TV that can load subtitles.

Copyrighted content is directly prohibited from being posted. Due to the copyright owner's request for some dramas, the cast button is gray, or the prompt "Screen casting is not supported due to copyright reasons" is displayed. This is a content-level limitation, and it doesn’t matter how good your home network is.

Member clarity limit. This is an old grudge: Starting from January 2023, iQiyi reduced the screen resolution of gold members to 480P. If you want high-definition screencasting, you have to upgrade to the more expensive platinum member. Users sued. In July 2024, the platform lost the first trial of the court. Up to now, the policies of each company are different. Tencent Video is the most lenient. It has basically canceled the restrictions on the resolution of the screen. Only some copyrighted content cannot be cast. Therefore, the screen projection quality suddenly becomes blurry. First check whether it is due to the membership level. Don’t blame the router in a hurry.

third floor: When the card is stuck in PPT, first identify who is pulling traffic.

Let me ask you a question before checking in.: Did you vote online or locally?

Use the online screen mirroring card to check the TV, not the mobile phone. As mentioned before, after clicking the TV button, the TV downloads the video itself, and the full signal of the mobile phone cannot help at all. My daughter-in-law is stuck while watching a TV show. The first thing I do is not restart the router, but watch the WiFi on TV - the TV in the living room is separated from the router by a wall, and the 2.4G signal is at -70dBm, and it gets stuck during the evening rush hour. Moving the TV closer, or connecting 5G to the TV, or running a network cable is more effective than anything else. Is the TV connected to WiFi or plugged in a network cable? I have actually tested that article. For the same drama, if the TV is moved from 2.4G edge to 5G close range, the bit rate can be increased several times.

Local screen projection card, calculate a bandwidth account. Local streaming really requires moving video data from a mobile phone or NAS to a TV. 1080P video sources generally require a sustained speed of around 8 MB, and 4K original disks can reach 60, 70 MB or even higher. The mobile phone is on the edge of 2.4G, with a negotiated speed of 72M, but the actual speed is often more than 20M, and 1080P is barely enough, and 4K is bound to be stuck. This set of signal binning and code rate accounts, How to choose between 2.4G and 5G Actual measured figures have been written in it. If the signal is not bad but still stuck, and the signal is stuck at eight or nine o'clock in the evening, it means the channel has crashed. How to choose a channel Use your phone to scan the surrounding areas for occupancy.

If you are not sure where the bottleneck is, let’s run a test on the TV side first. Speed ​​test ： The TV itself has been measured to have over 20 to 30 Mbit/s, and online 1080P is enough. ； As for local 4K, that one needs to go to 100Mbps. Another thing to mention, if you want to safely push local streaming, play movies on the NAS and play on the TV, each hop on the path must be wide enough. NAS pushes music to speakers This is the same principle, source to end is direct, and the intermediate device only forwards.

iPhone and Android screen mirroring are not the same thing

Apple has two sets, and many people use them interchangeably and think they are the same one.: The AirPlay button in the App pushes the video itself, saving power and maintaining stable image quality. ； The "screen mirroring" in the control center copies the entire screen. Whatever the phone does, the TV will display it. If the TV does not have AirPlay certification (most domestic TVs do not), you must install a receiving app on the TV so that your phone can see it in the list.

Android's "Wireless Screen Casting" uses Miracast, and the mobile phone is directly connected to the TV. The advantage is that it does not occupy the bandwidth of the home router, and it will not be affected by the router jam. The disadvantage is that some App content will black out and prevent you from casting. This is an anti-screen recording mechanism. If you install a screen casting app like Lebo on your TV and scan the QR code for pairing, it uses screen recording and push streaming. It can cast anything. However, the phone is hot, the picture quality is damaged, and there is a delay of a few tenths of a second. It is not suitable for watching TV dramas and playing games.

The most trouble-free thing about computer screencasting is the screencasting plug-in in the browser. It uses the DLNA method, which is the same as the mobile phone for online video casting.

Check the seats and check in this order fastest.

Give an order at the end: First, make sure the phone and TV are on the same network, then check the isolating switch, third, use the remote control to wake up the TV and resubmit, fourth, check the audio track subtitles, and fifth, activate the network. The first three steps don't cost a penny and can solve 90% of the screen overturning problems. That time, my wife "forgot" the neighbor's network in the mobile WiFi, and the TV immediately appeared in the list.