SSDV essentially snaps up JPEG files into pieces, cuts out metadata we do not need, and makes packets of 256 bytes. In those 256 it also includes Reed Solomon Forward Error Correction code, so that it can repair any badly received bits, up to 7%. This makes this method very error proof.
Different from SSTV
SSTV Is widely known, and is a analogue signal. SSDV is a digital signal, with bits that make up bytes that make up actual files.
Speed, Size and Efficiency
I have tried it from 50 bits per second to ~1200 bits per second (bits/second should actually be baud, im ignoring that for clarity). Currently the implemented method with decoding by DL-FLDIGI software is maxed out at 1200 baud due to software issues that arise if it is pushed any faster.
How i used it
The code has already been sucesfully tested from 36km altitude in a 2.5hour flight to the stratosphere. You can read about the Space Cmera Live 1 project here