Electronics > Projects, Designs, and Technical Stuff

Digital FPV video for drone racing

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mikeselectricstuff:
There is a lot of redundancy from one line to the next, so some sort of line-to-line delta compression might be worth investigating, as it could be very simple to encode and decode.

Also may be some mileage in multiple receivers working on a line-by-line basis, so as long as one receiver gets a good line, the whole frame will be correct. Receivers linked with gbit ethernet using raw packets (not TCP/IP) ought to be fast enough to handle this

ogden:

--- Quote from: mikeselectricstuff on January 23, 2019, 11:00:01 am ---There is a lot of redundancy from one line to the next, so some sort of line-to-line delta compression might be worth investigating, as it could be very simple to encode and decode.

--- End quote ---

Yes, indeed similar to h264 motion estimation can be used, but then low latency compressor becomes exponentially complex task.... unless video is ~80% centered crop of the sensor area, each frame is compressed in shifted coordinate system to match previous frame - so redundant image parts (if any) can be omitted, yet later frame is displayed in original coordinates. Kind of whole frame motion estimator. We may be on to something here.

[edit] This is more or less how digital steadycam is working, obviously it does not do "displayed in original coordinates" ;)


--- Quote ---Also may be some mileage in multiple receivers working on a line-by-line basis, so as long as one receiver gets a good line, the whole frame will be correct. Receivers linked with gbit ethernet using raw packets (not TCP/IP) ought to be fast enough to handle this

--- End quote ---

Yes, "digital diversity" shall be included into feature list. Thou we talked about 8pix vertical slice so (M)JPEG compression can be used. For 480p video slice could be vertical 16pix so whole frame is split into 30 packets. At 20Mbit & 120 FPS it is ~694 bytes/packet.

Marco:

--- Quote from: ogden on January 23, 2019, 10:33:48 am ---You offer to compress video with fast vertical panning using 292:1 compression? - You sound like those 21-st century teens who declare that there's no need for education/experience/skills other than trained thumbs and internet :)

--- End quote ---
You sound like someone who hasn't actually tried to convert some action cam footage to 2 Mbps. It's not pretty, but then neither is NTSC. That's at less than 1 bit per symbol, which is a tad pessimistic ... noise isn't that high in the NTSC footage.

--- Quote ---By 100% saturating data channel you are adding one more frame time
--- End quote ---
Nah, as I said you can probably slice encode. Get X lines, encode as slice, put on wire, decode as slice ... that's <3X lines delay.

120 fps isn't all that important, since displays which can actually do it are so sparse. The mobile phone panels which can do it are unobtainium, there's just some expensive square panels for VR glasses ... or you need to move up to 15.6" laptop panels.

ogden:

--- Quote from: Marco on January 23, 2019, 11:58:20 am ---
--- Quote from: ogden on January 23, 2019, 10:33:48 am ---You offer to compress video with fast vertical panning using 292:1 compression? - You sound like those 21-st century teens who declare that there's no need for education/experience/skills other than trained thumbs and internet :)

--- End quote ---
You sound like someone who hasn't actually tried to convert some action cam footage to 2 Mbps.

--- End quote ---

Yes, I admit that I did not try to compress 480p 120fps action cam footage into 2Mbps. Did you? Really? - You sound like you tried everything.


--- Quote ---Nah, as I said you can probably slice encode. Get X lines, encode as slice, put on wire, decode as slice ... that's <3X lines delay.

--- End quote ---

This is not how h264 you are promoting, works.


--- Quote ---120 fps isn't all that important, since displays which can actually do it are so sparse.

--- End quote ---

It is. You may need to re-read (or comprehend) my posts to understand why.

LaserSteve:
Would it not be easier to take the raw digital stream from the camera, encode it with something like Manchester 2 or similar telephone style 3 or 4 level polarity independent scheme, ie AMI or NRZI , transmit a sync word, and send keyed, AM, FM, Whatever,  it with one of the sidebands suppressed by a simple filter?  ie Vestigial  Sideband like an old TV modulator...  In other words, just  MAKE IT PSEUDO ANALOG? Decode with a  Costas Loop if needed, etc.. If need be mix with a pseudo-random stream to make it spread spectrum...  You would have no  error correction, no multipath protection, bandwidth is freaking huge, I know the downsides... Then just do diversity receive using a pilot carrier...

Might just work. I've seen far crazier stuff done in Ham Radio to get video across.

Expecting inbound laughter... in 5,4,3,2,1 ... But very low latency...

Steve 

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