Puzzled: went to a friend (has Apple Tv and a Macbook Pro 2017), he played a 8GB video file on his TV - and the file was on the Mac. WHAT?!

[idh1oi12jkl31jk2bgve3jk12b]

How is this possible? 

And yes, I made sure the file itself was on the mac, was not uploaded to the cloud, and when you close the lid (of the macbook), the movie will stop playing on the TV (via AppleTV app on Apple TV device). 

 

Is there a way that this is done on WiFi? My thinking is that it's impossible since the throughput would have to be INSANE. An 8GB file (hour and 30 minutes) is (i think) something like 90MB per Second. 

 

Confused. 

[Lightwreather]

Well, pretty certain it's airplay.

ANd WiFi last time I checked has a bandwidth of 600–9608 Mbit/s

SO it is entirely possible.

[idh1oi12jkl31jk2bgve3jk12b]

35 minutes ago, J-from-Nucleon said:

Well, pretty certain it's airplay.

ANd WiFi last time I checked has a bandwidth of 600–9608 Mbit/s

SO it is entirely possible.

 

pardon my ignorance, what are you saying that a WiFi network can send (9000/8 = 1125Mega BYTES per second - right?) over WIRELESS WAVES???

 

did I wake up in 2222?

 

[Levent]

3 minutes ago, idh1oi12jkl31jk2bgve3jk12b said:

 

pardon my ignorance, what are you saying that a WiFi network can send (9000/8 = 1125Mega BYTES per second - right?) over WIRELESS WAVES???

 

did I wake up in 2222?

 

Is this file 8 seconds long and is 9gigabytes? If not that math is wrong.

 

 

What is important for streaming and also quality is the bitrate, highest nitrate for blueray is 128mbps and Netflix at its best streams at 40-45mbps.

 

Assuming this is a 100second video file with no sound with constant 45mbps of bitrate, file size would be approximately 560mb.

 

 

So, this is even possible on a wifi4 connection.

[maremp]

1 hour ago, idh1oi12jkl31jk2bgve3jk12b said:

Is there a way that this is done on WiFi? My thinking is that it's impossible since the throughput would have to be INSANE. An 8GB file (hour and 30 minutes) is (i think) something like 90MB per Second. 

How are you surprised by that speed on a local network over a couple of meters, and not by the fact that you can stream a 4k video over the actual internet?

 

According to a calculator I found online, youtube 4k compression for 90 minutes of video comes at 29GB, almost 4x the size of what you're describing. Calculating for 1080p, it comes at 7.3GB, which is about the size you're describing. So are you seriously impressed by the fact that you can stream a 1080p video over wifi, when you're able to do that over internet + wifi, heck even via phone data transfer, for years? 

 

Also, your math is way off. 8GB = 8192MB, duration 1.5h = 90mins = 5400s, 8192MB / 5400s = 1.52MB/s. Even the almost 20 years old wifi 802.11g standard at 54mbit/s cap can handle that.

[idh1oi12jkl31jk2bgve3jk12b]

14 minutes ago, maremp said:

How are you surprised by that speed on a local network over a couple of meters, and not by the fact that you can stream a 4k video over the actual internet?

 

According to a calculator I found online, youtube 4k compression for 90 minutes of video comes at 29GB, almost 4x the size of what you're describing. Calculating for 1080p, it comes at 7.3GB, which is about the size you're describing. So are you seriously impressed by the fact that you can stream a 1080p video over wifi, when you're able to do that over internet + wifi, heck even via phone data transfer, for years? 

 

Also, your math is way off. 8GB = 8192MB, duration 1.5h = 90mins = 5400s, 8192MB / 5400s = 1.52MB/s. Even the almost 20 years old wifi 802.11g standard at 54mbit/s cap can handle that.

 

I appreciate this informative response!!!!!!!! Thank you (and sorry for my horrible math). 

 

Let me ask this: why is it then, that when the Mac uses Screen Mirroring, it lags like crazy? Even the mouse curser is VERY laggy, not to mention playing a video (un-viewable). 

 

[Eigenvektor]

2 minutes ago, idh1oi12jkl31jk2bgve3jk12b said:

Let me ask this: why is it then, that when the Mac uses Screen Mirroring, it lags like crazy? Even the mouse curser is VERY laggy, not to mention playing a video (un-viewable).

As @Levent said, bitrate matters. A video is usually highly compressed. It is also not a realtime application, so latency isn't really relevant and/or noticeable. As long as packets arrive at a constant rate, it doesn't matter whether they took 1ms or 1m to arrive at your computer (you would notice playback takes 1m to start, but after that it would still be smooth)

 

A remote desktop connection on the other hand is latency sensitive, i.e. you immediately notice when your mouse cursor lags behind. And since good compression takes time and compute power, the connection probably isn't as highly compressed (since that could add even more latency). So the bandwidth requirement may actually be higher than that of a video file.

[idh1oi12jkl31jk2bgve3jk12b]

3 minutes ago, Eigenvektor said:

As @Levent said, bitrate matters. A video is usually highly compressed. It is also not a realtime application, so latency isn't really relevant and/or noticeable. As long as packets arrive at a constant rate, it doesn't matter whether they took 1ms or 1m to arrive at your computer (you would notice playback takes 1m to start, but after that it would still be smooth)

 

A remote desktop connection on the other hand is latency sensitive, i.e. you immediately notice when your mouse cursor lags behind. And since good compression takes time and compute power, the connection probably isn't as highly compressed (since that could add even more latency). So the bandwidth requirement may actually be higher than that of a video file.

 

That is phenomenal! Thank you so much! 

 

(me and my friend were arguing over this for like 20 minutes yesterday with no conclusion, so thanks for that!!!) 

 

EDIT: to be honest I am still surprised by the agility of WiFi in transferring data this quickly but I guess I need a good slap in the face. 

[maremp]

1 hour ago, idh1oi12jkl31jk2bgve3jk12b said:

Let me ask this: why is it then, that when the Mac uses Screen Mirroring, it lags like crazy? Even the mouse curser is VERY laggy, not to mention playing a video (un-viewable). 

 

To mirror a screen, the technology, either airplay or anything else, has to do the following:

1. Capture the real-time recording of the screen. 
2. Compress the video for faster transmission.
3. Send the video over the network.
4. The remote device (TV, apple TV, etc.) has to decode the video and then play it back.

The resolution of laptops is quite large, e.g. the new 14" macbook has native resolution of 3024x1964. Even when running it at 2x scaled (default), that's 1512x982, that's ~72% of 1080p resolution. It takes a lot of processing to achieve that, and if the cpu is not fast enough, it has to drop frames or it will just keep lagging behind. That's why the computer gets so hot when doing any kind of screen sharing, e.g. you might have noticed it with zoom or other chat apps if you ever use those. 

The lower framerate or dropped frames are why it feels laggy, especially with a video where you notice immediately because it breaks the continuity. It's like a fps drop when gaming, but worse.

 

But when playing back a video via apple TV, the video has some special properties that help with smooth playback. It's already compressed so the device can skip first two steps and just send it over the network. And the device can send parts of the video in advance, for example, it sends chunks of one minute, and when 30s in, it will send next minute and so on (I made up these numbers as an example). This way, even it there is a delay in the network, there is some video to play back and you won't notice any stutter. And in the rare cases when it does, you'll see the loading spinner (the good ol' buffering). 

With screen mirroring, you cannot do that because you can't record into the future and send video ahead of time. Even when playing back a video, the device still has to record the screen in realtime. 

[idh1oi12jkl31jk2bgve3jk12b]

4 hours ago, maremp said:

To mirror a screen, the technology, either airplay or anything else, has to do the following:

1. Capture the real-time recording of the screen. 
2. Compress the video for faster transmission.
3. Send the video over the network.
4. The remote device (TV, apple TV, etc.) has to decode the video and then play it back.

The resolution of laptops is quite large, e.g. the new 14" macbook has native resolution of 3024x1964. Even when running it at 2x scaled (default), that's 1512x982, that's ~72% of 1080p resolution. It takes a lot of processing to achieve that, and if the cpu is not fast enough, it has to drop frames or it will just keep lagging behind. That's why the computer gets so hot when doing any kind of screen sharing, e.g. you might have noticed it with zoom or other chat apps if you ever use those. 

The lower framerate or dropped frames are why it feels laggy, especially with a video where you notice immediately because it breaks the continuity. It's like a fps drop when gaming, but worse.

 

But when playing back a video via apple TV, the video has some special properties that help with smooth playback. It's already compressed so the device can skip first two steps and just send it over the network. And the device can send parts of the video in advance, for example, it sends chunks of one minute, and when 30s in, it will send next minute and so on (I made up these numbers as an example). This way, even it there is a delay in the network, there is some video to play back and you won't notice any stutter. And in the rare cases when it does, you'll see the loading spinner (the good ol' buffering). 

With screen mirroring, you cannot do that because you can't record into the future and send video ahead of time. Even when playing back a video, the device still has to record the screen in realtime. 

 

this is am amazingly informative answer, thank you so much for sharing this info! 

i am a bit wiser now. 

tbh this makes me want to run the Plex sotfware on a raspberry pi device at home just to try this out. 

[maplepants]

AirPlay is pretty handy for other stuff too. Back before it was built into macOS, I used an app called AirServer so that I could AirPlay my phone to my Mac, and then share that screen in a meeting I was taking from there. Super handy for anyone in mobile development. 

 

AirServer works on Windows too and I recommend it to every mobile dev. Trying to share the simulator or your Android emulator is terrible, especially if you're trying to demonstrate the nature of or fix for a device specific bug.