Strip headers from VITA-49 packets and dump the raw I/Q data contained within

vita_extract.py

import sys
import struct
import requests

# some details from https://github.com/RedhawkSDR/VITA49/blob/master/cpp/include/BasicVRTPacket.h

def parse_vita_float(radix, bits):
    # https://github.com/RedhawkSDR/VITA49/blob/a7230bcbd3547733be669b7c745eb7d9b0e17d25/cpp/include/VRTMath.h#L471
    div = float(1 << radix)
    return float(bits) / div

def parse_vita_double(bits):
    return parse_vita_float(20, bits)

def parse_vita_f16(bits):
    return parse_vita_float(7, bits)

if __name__ == "__main__":
    # Usage: python3 vita_extract.py {vita49_input_filename} {raw_output_filename}
    infn = sys.argv[1]
    if infn.startswith('http'):
        req = requests.get(infn, stream=True)
        if not req.ok:
            raise Exception(str(req))
        inf = req.raw
    else:
        inf = open(infn, 'rb')

    with open(sys.argv[2], 'wb') as outf:
        while True:
            hdrb = inf.read(4)
            if not hdrb:
                break
            assert len(hdrb) == 4

            h = int.from_bytes(hdrb, 'big')
            typ = h >> 28

            sz = h & 0xffff
            sz *= 4

            # size includes the 4 bytes we already read
            everything = hdrb + inf.read(sz - 4)
            assert len(everything) == sz

            if typ == 1:
                #hdr = everything[:7*4]
                data = everything[7*4:]
                outf.write(data)
            elif typ == 4:
                ctx = everything[7*4:]
                # context
                # https://github.com/microsoft/azure-software-radio/blob/main/gr-azure-software-radio/lib/difi_source_cpp_impl.cc#L314
                unpacked = list(struct.unpack('!LLQQQQLLQQLLQ', ctx))
                names = ['cif', 'rp', 'bw', 'ifref', 'rfref', 'ifoff', 'refl', 'gain', 'rate', 'tsadj', 'tscal', 'indic', 'payloadfmt']
                unpacked = dict(zip(names, unpacked))
                unpacked['cif'] = hex(unpacked['cif'])
                unpacked['rp'] = hex(unpacked['rp'])
                unpacked['bw'] = parse_vita_double(unpacked['bw'])
                unpacked['ifref'] = parse_vita_double(unpacked['ifref'])
                unpacked['rfref'] = parse_vita_double(unpacked['rfref'])
                unpacked['ifoff'] = parse_vita_double(unpacked['ifoff'])
                unpacked['refl'] = parse_vita_f16(unpacked['refl'])
                # unsure of this
                unpacked['gain'] = {1: parse_vita_f16(unpacked['gain'] & 0xffff), 2: parse_vita_f16(unpacked['gain'] >> 16)}
                unpacked['rate'] = parse_vita_double(unpacked['rate'])
                unpacked['indic'] = {'reflock': bool(unpacked['indic'] & (1 << 17))}
                unpacked['payloadfmt'] = {'bitdepth': (unpacked['payloadfmt'] >> 32 & 0x1f) + 1}
                print(unpacked)