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480mbps isn't enough for good quality video? It's 3.75x the maximum bitrate of a 4K Blu Ray. It should be fine. It can't be lossless, but it should be damn high

480mbps isn't enough for good quality video? It's 3.75x the maximum bitrate of a 4K Blu Ray. It should be fine. It can't be lossless, but it should be damn high quality.

orbital-decay 3y ago
I was going to say something about MJPEG, but it looks like UVC supports H.264 for a decade already. I guess I was confused by the cheap USB 2.0 webcams, they mostly use MJPEG and yes it's utter trash. Still, good webcams use USB 3.0 and no chroma subsampling, to avoid recompression and enable certain tricks. I hope the YUV 4:4:4 mode will be supported in this, for those who have the speed and want chromakeys/non-blurry reds.
duskwuff 3y ago
> 480mbps isn't enough for good quality video? It's 3.75x the maximum bitrate of a 4K Blu Ray. Webcams need to be very near real-time to be useful. That severely limits what kinds of compression you can use on the video stream.
- ClassyJacket 3y ago
  That's absolutely true but I still very much doubt it's so bad that you would exceed 480mbps even on a decent resolution stream. We're not talking multiple orders of magnitude difference. Like... if all else fails just send every frame as a separate image with a fast encoder and you've still got 1.6 megabytes for each. Steam in-home streaming needs to be realtime too, but is very playable, and most people aren't realistically getting 480mbps out of their wifi. 4k I don't know... 1080p no problem. Don't most phones have dedicated hardware video encoders on their SoC now anyway?
  - rcme 3y ago
    You could transmit raw rgba pixels at 1920x1080 and 60 fps in less than 500 mbps.
    - ClassyJacket 3y ago
      I don't think so... my maths (for RGB, no need for alpha channel) comes out to 2,847mbps. Did you accidentally switch megabits and megabytes?
      - duskwuff 3y ago
        And don't forget that 480 Mbps is the line rate. Practical throughput to a device will be substantially less, especially if other devices are on the bus.
GuB-42 3y ago
To make a point, early webcams were USB 1.0, 12Mbps maximum, and it was enough for SD-quality video. USB 2.0 is 40x faster, which, assuming similar encoding (i.e. 20 year old tech), should be more than enough for 1080p video. It should be enough to best any laptop webcam, which are usually USB2 internally, but with worse optics and without the processing power of a smartphone behind it. Using more fancy encoding, 4k should be no problem, even with a bit of headroom for on-device encoding and low latency.
- Dalewyn 3y ago
  >without the processing power of a smartphone behind it. Considering the cheapest of desktop/laptop CPUs and iGPUs are more powerful than the best mobile CPUs and GPUs, this is a problem with the encoders and video chat software involved.
  - Retric 3y ago
    The best cellphone CPU’s easily beat cheap laptops’s from a few years ago that used low end 10th gen Intel chips. They don’t have the terminal budget to quite beat today’s chips, but it’s much closer than you might expect. That might seem unfair, but many people replace their phones far more frequently than their computers.
  - GuB-42 3y ago
    I meant the chip between the builtin laptop webcam and its internal USB2 connection, which is typically a tiny, dedicated IC. Smartphones cameras are not USB2, they are, I think, directly connected to a powerful SoC. The USB2 link is for sending data to the computer after the smartphone has processed it with all the might of its main processor.
  - kccqzy 3y ago
    Have you been living under a rock? The encoders have been hardware based for more than a decade.
ianburrell 3y ago
The video out isn't over USB2 data but over the high speed lines that are for USB3 and alternate mode. It should be possible to have DisplayPort output but with USB2 data. In fact, we know it is possible because the iPhone 15 does it. It has USB2 data speeds but 4K Displayport.
kccqzy 3y ago
Indeed Apple CarPlay is entirely based on sending H.264 video over IP over USB 2.0 and it's very good quality with low lag. It's absolutely good enough for webcam style usage. https://devstreaming-cdn.apple.com/videos/wwdc/2016/722x2eefo3u2rp8k8qs/722/722_developing_carplay_systems_part_1.pdf?dl=1 https://devstreaming-cdn.apple.com/videos/wwdc/2016/722x2eef...

480mbps isn't enough for good quality video? It's 3.75x the maximum bitrate of a 4K Blu Ray. It should be fine. It can't be lossless, but it should be damn high quality.

orbital-decay 3y ago

I was going to say something about MJPEG, but it looks like UVC supports H.264 for a decade already. I guess I was confused by the cheap USB 2.0 webcams, they mostly use MJPEG and yes it's utter trash. Still, good webcams use USB 3.0 and no chroma subsampling, to avoid recompression and enable certain tricks. I hope the YUV 4:4:4 mode will be supported in this, for those who have the speed and want chromakeys/non-blurry reds.

duskwuff 3y ago

> 480mbps isn't enough for good quality video? It's 3.75x the maximum bitrate of a 4K Blu Ray. Webcams need to be very near real-time to be useful. That severely limits what kinds of compression you can use on the video stream.

ClassyJacket 3y ago
That's absolutely true but I still very much doubt it's so bad that you would exceed 480mbps even on a decent resolution stream. We're not talking multiple orders of magnitude difference. Like... if all else fails just send every frame as a separate image with a fast encoder and you've still got 1.6 megabytes for each. Steam in-home streaming needs to be realtime too, but is very playable, and most people aren't realistically getting 480mbps out of their wifi. 4k I don't know... 1080p no problem. Don't most phones have dedicated hardware video encoders on their SoC now anyway?
- rcme 3y ago
  You could transmit raw rgba pixels at 1920x1080 and 60 fps in less than 500 mbps.
  - ClassyJacket 3y ago
    I don't think so... my maths (for RGB, no need for alpha channel) comes out to 2,847mbps. Did you accidentally switch megabits and megabytes?
    - duskwuff 3y ago
      And don't forget that 480 Mbps is the line rate. Practical throughput to a device will be substantially less, especially if other devices are on the bus.

GuB-42 3y ago

To make a point, early webcams were USB 1.0, 12Mbps maximum, and it was enough for SD-quality video. USB 2.0 is 40x faster, which, assuming similar encoding (i.e. 20 year old tech), should be more than enough for 1080p video. It should be enough to best any laptop webcam, which are usually USB2 internally, but with worse optics and without the processing power of a smartphone behind it. Using more fancy encoding, 4k should be no problem, even with a bit of headroom for on-device encoding and low latency.

Dalewyn 3y ago
>without the processing power of a smartphone behind it. Considering the cheapest of desktop/laptop CPUs and iGPUs are more powerful than the best mobile CPUs and GPUs, this is a problem with the encoders and video chat software involved.
- Retric 3y ago
  The best cellphone CPU’s easily beat cheap laptops’s from a few years ago that used low end 10th gen Intel chips. They don’t have the terminal budget to quite beat today’s chips, but it’s much closer than you might expect. That might seem unfair, but many people replace their phones far more frequently than their computers.
- GuB-42 3y ago
  I meant the chip between the builtin laptop webcam and its internal USB2 connection, which is typically a tiny, dedicated IC. Smartphones cameras are not USB2, they are, I think, directly connected to a powerful SoC. The USB2 link is for sending data to the computer after the smartphone has processed it with all the might of its main processor.
- kccqzy 3y ago
  Have you been living under a rock? The encoders have been hardware based for more than a decade.

ianburrell 3y ago

The video out isn't over USB2 data but over the high speed lines that are for USB3 and alternate mode. It should be possible to have DisplayPort output but with USB2 data. In fact, we know it is possible because the iPhone 15 does it. It has USB2 data speeds but 4K Displayport.

kccqzy 3y ago

Indeed Apple CarPlay is entirely based on sending H.264 video over IP over USB 2.0 and it's very good quality with low lag. It's absolutely good enough for webcam style usage. https://devstreaming-cdn.apple.com/videos/wwdc/2016/722x2eefo3u2rp8k8qs/722/722_developing_carplay_systems_part_1.pdf?dl=1 https://devstreaming-cdn.apple.com/videos/wwdc/2016/722x2eef...