import sys,time,struct,os
BODY=bytes([6,14,43,52,2,5,1,1,13,1,2,1,1,3])
ITS=bytes([6,14,43,52,2,83,1,1,13,1,2,1,1,16,1,0])
def get_frames(p):
  try:
    sz=os.path.getsize(p)
    if sz<50000:return 0
    with open(p,"rb") as f:
      f.seek(max(0,sz-3000000));d=f.read()
    pos=len(d)
    while True:
      i=d.rfind(BODY,0,pos)
      if i<0:break
      pos=i;bs=i+16;b0=d[bs]
      if b0==0x83:bl,bv=4,struct.unpack(">I",b"\x00"+d[bs+1:bs+4])[0]
      elif b0==0x82:bl,bv=3,struct.unpack(">H",d[bs+1:bs+3])[0]
      else:bl,bv=1,b0
      if len(d)<bs+bl+48:break
      ibc=struct.unpack(">Q",d[bs+bl+40:bs+bl+48])[0]
      if not ibc:continue
      itd=d[i+16+bl+bv:i+16+bl+bv+ibc]
      ii=itd.find(ITS)
      if ii<0:break
      ib0=itd[ii+16]
      if ib0==0x83:ivl,ivv=4,struct.unpack(">I",b"\x00"+itd[ii+17:ii+20])[0]
      elif ib0==0x82:ivl,ivv=3,struct.unpack(">H",itd[ii+17:ii+19])[0]
      else:ivl,ivv=1,ib0
      sd=itd[ii+16+ivl:ii+16+ivl+ivv];p2=isp=dur=0
      while p2<len(sd)-3:
        t=struct.unpack(">H",sd[p2:p2+2])[0];l=struct.unpack(">H",sd[p2+2:p2+4])[0]
        if p2+4+l>len(sd):break
        v=sd[p2+4:p2+4+l]
        if t==0x3F0C and l==8:isp=struct.unpack(">q",v)[0]
        elif t==0x3F0D and l==8:dur=struct.unpack(">q",v)[0]
        p2+=4+l
      return max(0,isp+dur)
  except:return 0
  return 0
mxf=sys.argv[1]
while not os.path.exists(mxf) or os.path.getsize(mxf)<20000:time.sleep(0.3)
with open(mxf,"rb") as f:hdr=f.read(200000)
offs=[]
for pat in [b"\x02\x02\x00\x08\xff\xff\xff\xff\xff\xff\xff\xff",b"\x30\x02\x00\x08\xff\xff\xff\xff\xff\xff\xff\xff"]:
  p=0
  while True:
    i=hdr.find(pat,p)
    if i<0:break
    offs.append(i+4);p=i+1
print("[dur-patch] %d Duration fields"%len(offs),flush=True)
def patch(val):
  if not offs:return
  try:
    with open(mxf,"r+b") as f:
      for o in offs:f.seek(o);f.write(struct.pack(">q",val))
  except Exception as e:print("[dur-patch] err:",e,flush=True)
# Premiere rejects a growing OP1a/RDD9 whose header Duration is -1 on import
# (bmx thread 87ac5750: Premiere prefers 0). raw2bmx writes -1 at clip-open, so
# overwrite every -1 with 0 immediately, BEFORE any frames exist, then track the
# live frame count every 3s.
patch(0)
print("[dur-patch] Duration=0 (initial)",flush=True)
while True:
  time.sleep(3)
  fc=get_frames(mxf)
  if fc>0:
    patch(fc)
    print("[dur-patch] Duration=%d"%fc,flush=True)