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headersquash.py combines running headers used to pad early broadcasts.

In the early 80s, BBC transmissions repeated the packet headers multiple
times. This combines them using bitwise_mode. eg:

./t42cat.py 0001/t42/ | ./headersquash.py | ./demux.py h | less -r

This will only work if the transmission has only one magazine and
it especially won't do anything useful with later ITV broadcasts,
which pad using headers for page 1ff followed by one real header.
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1 parent e8b4e0c commit 1c4a520a599598c82df333711ed301f4ecad632d @ali1234 committed Feb 19, 2012
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  1. +48 −0 headersquash.py
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+#!/usr/bin/env python
+
+# * Copyright 2011 Alistair Buxton <a.j.buxton@gmail.com>
+# *
+# * License: This program is free software; you can redistribute it and/or
+# * modify it under the terms of the GNU General Public License as published
+# * by the Free Software Foundation; either version 3 of the License, or (at
+# * your option) any later version. This program is distributed in the hope
+# * that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# * GNU General Public License for more details.
+
+# Squash repeated headers
+# Usage: cat <data> | ./headersquash.py | ./demux.py h | ./printer.py
+
+import sys
+import numpy as np
+
+from util import mrag, bitwise_mode, page
+
+def dump_headers(headers):
+ if len(headers) > 1:
+ ans = bitwise_mode([np.fromstring(h, dtype=np.uint8) for h in headers])
+ ans = "".join([chr(x) for x in ans])
+ else:
+ ans = headers[0]
+
+ sys.stdout.write(ans)
+
+if __name__=='__main__':
+
+ headers = []
+
+ while(True):
+ tt = sys.stdin.read(42)
+ if len(tt) < 42:
+ exit(0)
+ ((m,r),e) = mrag(np.fromstring(tt[:2], dtype=np.uint8))
+ (p,e1) = page(np.fromstring(tt[2:4], dtype=np.uint8))
+ if r == 0:
+ headers.append(tt)
+ else:
+ if len(headers) > 0:
+ dump_headers(headers)
+ headers = []
+ sys.stdout.write(tt)
+ sys.stdout.flush()
+

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