Electronics > Projects, Designs, and Technical Stuff

Digital FPV video for drone racing

<< < (27/28) > >>

Kilrah:
One of the requirements is having 8 systems working together in a relatively narrow ISM band, so "freaking huge" bandwidth won't cut it.

BTW that already exists (WHDI-like systems) but while RF latency is almost 0 the use of standard input/output interfaces and camera/displays still introduces quite a bit of it in the total. And the transmission performance is meh at more than short distances.

Marco:

--- Quote from: ogden on January 23, 2019, 12:46:41 pm ---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.

--- End quote ---
vlc -I dummy -vvv "xxx.mp4" --sout=#transcode{venc=x264,fps=60,vcodec=h264,vb=2048}:standard{access=file,mux=ts,dst=yyy.mp4}

Downloading a 60 fps movie off youtube is a bit tricky, all the new firefox extensions suck ... but YouTube Video and Audio Downloader can do it (you have to play a bit of a guessing game which it is).

--- Quote ---This is not how h264 you are promoting, works.

--- End quote ---
Yes it does. Slices are in principle designed for parallel encoding/decoding, but they work fine to reduce latency too, x264 went down the same path when they were paid to create a low latency encoder for network gaming.

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

--- End quote ---
I know why higher framerate lowers latency, but it's simply not an option for now in a system at sensible cost/size. So framelocked encoding/decoding chasing/leading the scanline at 60 Hz is the best you can do.

Marco:

--- Quote from: LaserSteve on January 23, 2019, 04:07:53 pm ---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?

--- End quote ---

To do it cheaply it's by far the easiest to use the existing 5.8 GHz chipsets ... in which case you get an amplitude only input/output for a FM encoder/decoder.

For what it's worth, the RTC6715 seems pretty good at AGC at least, just out of hand rejecting it as crap is presumptuous.

hexahedron:
Hey again! I just had a fantastic idea, let's see what will be thought of it! Pure digital is for sure not going to be very easy to accomplish, but what if we just improved the analog standard? Obviously ntsc has a lot of issues when it comes to how color is encoded, and I could fix that, but I have a better idea. What if we were to apply the discrete cosine tranform to 8x8 blocks, but them transmit them as an analog signal? We could assign more time to the more important parts of the image (IE: low frequencies and brightness) and on the other end, we could do a ton of over sampling. This would result in high frequency parts of the image being lost first, giving the effect of higher levels of jpeg compression as signal quality is lost. Thoughts?

ogden:

--- Quote from: Marco on January 23, 2019, 05:41:59 pm ---So framelocked encoding/decoding chasing/leading the scanline at 60 Hz is the best you can do.

--- End quote ---

What's the point of building 60Hz digital system if by design it's latency cannot be lower than existing NTSC (60Hz half-frames)?

[edit] Thank you for h.264 slices info. It makes sense to use just "standard" h264 for this application. Most likely you wanted to post following link: https://en.wikipedia.org/wiki/Flexible_Macroblock_Ordering. I wonder - does rPI h264 encoder have slicing support?

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod