7d61c2f8f1
External vectors written by permissively licensed encoders at pinned revisions from synthetic pictures (tools/make_external.sh, provenance.json), generated vectors and negative controls, the facts each encoder was asked for, the LCEVC streams fetch.sh fetches by digest, and format_probe_verify.py, written from the two texts. Co-Authored-By: Claude Opus 5.5 <[email protected]>
66 lines
2.3 KiB
Python
66 lines
2.3 KiB
Python
"""Two framing helpers of make_external.sh.
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python3 -I frame.py jxsvideo <out> <w> <h> <fps_num> <fps_den> <codestreams>
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Splits a file of consecutive JPEG XS codestreams (each with its length in its
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picture header's Lcod, as a constant-bit-rate encoder writes) and writes them in
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wai.video.jxs's framing: five u32 little-endian values n, h, w, fps_num, fps_den,
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then each codestream preceded by its u32 little-endian length (format-probes §3.3).
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python3 -I frame.py base <in> <out>
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Keeps the NAL units of an H.265 Annex B byte stream whose nuh_layer_id is 0: the
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base layer of a multilayer bitstream, each NAL unit after a four-byte start code.
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"""
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import struct
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import sys
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def codestreams(b):
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out, at = [], 0
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while at < len(b):
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if b[at:at + 2] != b"\xff\x10" or b[at + 2:at + 4] != b"\xff\x50":
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raise SystemExit("no SOC and CAP at %d" % at)
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lcap = struct.unpack(">H", b[at + 4:at + 6])[0]
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pih = at + 4 + lcap
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if b[pih:pih + 2] != b"\xff\x12":
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raise SystemExit("no PIH at %d" % pih)
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lcod = struct.unpack(">I", b[pih + 4:pih + 8])[0]
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if lcod == 0:
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raise SystemExit("a codestream without Lcod: the encoder was not at a constant rate")
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out.append(b[at:at + lcod])
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at += lcod
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return out
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def jxsvideo(out, w, h, num, den, src):
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cs = codestreams(open(src, "rb").read())
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data = struct.pack("<5I", len(cs), int(h), int(w), int(num), int(den))
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for c in cs:
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data += struct.pack("<I", len(c)) + c
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open(out, "wb").write(data)
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def nal_units(b):
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starts, i = [], 0
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while i + 2 < len(b):
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if b[i] == 0 and b[i + 1] == 0 and b[i + 2] == 1:
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starts.append(i + 3)
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i += 3
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else:
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i += 1
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units = []
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for k, s in enumerate(starts):
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e = starts[k + 1] - 3 if k + 1 < len(starts) else len(b)
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while e > s and b[e - 1] == 0:
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e -= 1
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units.append(b[s:e])
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return units
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def base(src, out):
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keep = [u for u in nal_units(open(src, "rb").read()) if ((u[0] << 8 | u[1]) >> 3) & 0x3F == 0]
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open(out, "wb").write(b"".join(b"\x00\x00\x00\x01" + u for u in keep))
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if __name__ == "__main__":
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{"jxsvideo": jxsvideo, "base": base}[sys.argv[1]](*sys.argv[2:])
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