While technically it is possible to convert JPEG images to SRF format (Sony RAW), it's typically a pointless endeavor, unless you need that for some particular purpose.
You can find graphics/photo editors that support saving to SRF format, so if you truly desire, jpeg to srf conversion is doable, but the resulting file will lack any metadata that would be otherwise saved by the Sony camera.
But in any case, the best way how to produce SRF files is to actually record these using Sony digital camera.
Updated: August 14, 2023