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Image Splicing Idea for FPV Flying?

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Carbon_Rod

Sun Jul 29 2012, 09:24PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155

Actually they do, depending on the media stream encapsulation and transmitter:

1. simply ignore lost fragments (allow frame data to overlap)
2. replace lost media areas with green squares or garbage (like your TV)
3. drop the corrupt frame
4. recover the lost fragments using transceiver buffer
5. recover the lost fragments using network protocols
6. adjust band to minimize collision interference
7. lower resolution bandwidth to increase ECC loss redundancy

Pinky's Brain

Sun Jul 29 2012, 09:34PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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wrote ...

Actually they do, depending on the media stream encapsulation and transmitter:

Want to qualify who "they" are with a concrete example :)

Carbon_Rod

Mon Jul 30 2012, 03:59AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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DARPA's challenges inspired numerous companies to create industrial sensors:

Not sure why you are interested in a "concrete example", but here is google's answer:

HD camera capture can be low cost, but it really depends on the intended application.

2Spoons

Mon Jul 30 2012, 04:38AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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There seem to be quite a few cameras out there with H.264 encoding built in. That would greatly lower the data rate. whether there is one small enough is another story.

Hazel1919

Mon Jul 30 2012, 08:05AM

Registered Member #1376 Joined: Wed Mar 05 2008, 08:31AM
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The quote below, which I found in this thread

I think sums up the predicament pretty well. Perhaps the technology is available, but not yet affordable or practical.

This is why I proposed the idea in the first post. If people can get a low quality analogue video link at 1km+, can we not use two transmitters and share the footage over both to get 2x the quality using 2x the bandwidth? We will still have 1km+ range then and the only special equipment we need is an image splitter and image splicer, of which the splitter need be onboard.

"My conclusion is that using current technology, HD transmission for FPV is not possible. If by "HD" you mean the uncompressed digital video signal, like it is transmitted over an HDMI cable, the bandwidth of that signal is approximately 4Gbps. It will be difficult to transmit this amount of data over a wireless link. You may be able to use some UWB technology but then the range is insufficient for FPV. You could of course compress the video, using e.g. H.264, to a reasonable bitrate, say 3Mbps. But then you have the problem that you need to put a quite powerful computer in the heli to compress video and the compression/decompression also introduces a delay (among other things bc. motion compensated coding is used for video compression), which makes it pretty much unusable for FPV. Anyways, even if you had some fantasy low delay video compression technology, you still need to transmit 3Mbps over a long distance, which is difficult to do reliably.

Digital video transmission has also some other problems. One is that when you get out of range you will suddenly lose the whole video link without any warning, which is much worse than with analog video where you get more and more distortions as you approach the maximum transmission range."

Carbon_Rod

Mon Jul 30 2012, 08:32AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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meh, several Mbps at "50km" in theory is available to the public (few hundred on eBay).

Kind of pointless given the broadcast power limits on the selected unlicensed bands.

It is possible to build by a hobbyist...
There is just an huge fine waiting for the person who does it.

Cheers,

Hazel1919

Mon Jul 30 2012, 09:45AM

Registered Member #1376 Joined: Wed Mar 05 2008, 08:31AM
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This video gives a very good illustration of the difference between the HD recording and the live output.

The current conventional FPV setup that most people use involves a camera sensor unit connected to a 5.8Ghz

or 1.2Ghz Video Tx, each being connected to the main battery.

Pinky's Brain

Mon Jul 30 2012, 05:07PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

wrote ...
This is why I proposed the idea in the first post. If people can get a low quality analogue video link at 1km+, can we not use two transmitters and share the footage over both to get 2x the quality using 2x the bandwidth?

If you want to increase the resolution both horizontally and vertically you will need 4 analogue channels of course ...

wrote ...
"you still need to transmit 3Mbps over a long distance, which is difficult to do reliably."

With a tracking antenna (for which ready made solutions are already available I see) it could probably be done ... and you could always have an analogue backup channel.

PS. 1.2 GHz is not an ISM band ... I question the legality.

Steve Conner

Mon Jul 30 2012, 07:02PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Was there ever a standard for analogue HD video? I think a digital transmitter (or indeed a digital encoder) would be heckuva heavy and power hungry.

From an information theoretic point of view, there's no difference between 4 cameras feeding 4 transmitters, and one camera with 4x the pixels, feeding a transmitter with 4x the bandwidth and 4x the output power. The RF power budget and range would be the same.

From a practical point of view, one big system might be lighter than four small ones, which would have many components in quadruplicate (for example 4 lenses)

If you are serious about experimenting with novel transmission systems, you really ought to get a ham license. That's what it's for! You could run hundreds of watts of transmit power legally.

Hazel1919

Tue Jul 31 2012, 09:12AM

Registered Member #1376 Joined: Wed Mar 05 2008, 08:31AM
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"If you want to increase the resolution both horizontally and vertically you will need 4 analogue channels of course ..."

It could just be a matter of aspect ratio (16:4.5 + 16:4.5)? Data transmission is proportional to bandwidth.

Steve, a ham license would be fantastic, but alas I live in France now and need to learn the language before that! What you say is absolutely correct about integrating it into one unit, I am just thinking from a prototype point of view. If this works there should be products like it for sale?

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