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Comment by magnat | Hacker News Reader

> Low res analog video -> high res digital video

Major benefit of analog video is a progressive degradation of quality as a signal gets weaker and almost instant reacquisition after a complete dropout. I'm curious to see how DJI competes with that on a digital video.

> ~5 minutes fly time -> ~20 minutes fly time

For FPV racing that's rather a downgrade. Ideally you'd like to land with almost empty battery right after finishing the course. Any leftover charge is a dead weight that only slows you down. But then again - I don't think this drone will be used in competitive FPV racing.

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>Major benefit of analog video is a progressive degradation of quality as a signal gets weaker and almost instant reacquisition after a complete dropout. I'm curious to see how DJI competes with that on a digital video.

The good news is that you can find that out right now. DJI HD FPV has been available for over a year, this is just their first drone offering in the category.

The short answer is that it degrades very gracefully. They have what they call 'focus mode', where the edges of the video lose quality before the middle (where the data matters the most). Once you've used up that signal degradation threshold the rest of the frame slowly degrades to a lower bitrate, and then after that latency starts rising.

After flying analog for 5 years it only took me about 1 day to strongly prefer the DJI FPV video solution. The range is far better, and the video is mind-blowingly clear when compared to analog. On anything but my racing specific drones I have been installing the DJI HD FPV system instead of normal analog gear.

> it degrades very gracefully

Pretty convincing comparison by Joshua Bardwell:

Shark Byte: https://youtu.be/9iKc2v05blw?t=926

vs DJI: https://youtu.be/9iKc2v05blw?t=1046

vs analog: https://youtu.be/9iKc2v05blw?t=1227

> They have what they call 'focus mode', where the edges of the video lose quality before the middle (where the data matters the most).

If the latency is low enough it would be nice if they could incorporate eye tracking into that in the future, and move around the high quality region with your eyes. And maybe feed it from a gimballess 360 camera so you have full freedom to look around. Stereo cameras would also be nice, maybe with some differential compression between eyes to keep bandwidth down (would need a gimbal for that most likely, to keep line between cameras horizontal).

As you say at the end, this isn't a drone for racing. I think this drone would mostly be for videographers wanting to add FPV-style shots to their arsenal. I shoot with a Mavic 2 (https://serio.com.au/) and if there was a bit more of a market for the FPV look in the work I typically do, I'd grab one of these right away.

At this point though it's probably something I'd look at closer once I have a bit more spare time and can think about situations where it might be applied.

> Major benefit of analog video is a progressive degradation of quality as a signal gets weaker and almost instant reacquisition after a complete dropout. I'm curious to see how DJI competes with that on a digital video.

Waiting for a degradation tolerant codec.

Old MPEGs were, as they had broadcast use in mind, but even 264 blow them out of the water on compression nowadays.

Loss tolerant codec + modern channel coding will likelly outrange analog for quality picture

SVC profiles target bandwidth degradation, but yeah nothing really recovers from random dropouts anywhere in the steam like analog...

Lots of I-frames, I guess...

Lots of I-frames means you effectively revert to a little more sophisticated version of mjpeg

A cheap, and dirty hack I can think of is to dynamically adjust the bitrate for the bandwidth after FEC/channel coding. Margins will still have to be quite huge I believe.

On progressive degradation, perhaps the digital video output could be adapted with an indication of the error rate (which usually get corrected in the background until it reaches a threshold where the errors are too great)

Or perhaps the signal strength or SNR.

These parameters are available but not usually displayed.

Isn't the edge being there's almost no delay in analog video transmission? While the best DJI can do is like 130 ms.

They say their delay for this drone is 28ms, and I'm inclined to believe them.

I've been flying DJI HD FPV for about a year now and yes - latency hovers around 24ms in good conditions. The range also blows away my normal analog gear.

> Any leftover charge is a dead weight that only slows you down.

Uh? Can you explain this?

Presumably not literally like in the case of a rocket or formula 1, but also literally as in, I could have used a lighter battery with less charge that goes faster

If you have leftover charge after you land it means you could have used a smaller (and thus lighter) battery, which would have let you fly faster.

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