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@TimSC TimSC/mjpeg.py
Last active Aug 22, 2018

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Python code to parse a JPEG structure and to convert Motion JPEG/MJPG binary data to standard JPEG. This code may be used under CC0.
import struct
huffmanSegment = '\xFF\xC4\x01\xA2\x00\x00\x01\x05\x01\x01\x01\x01'\
'\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x01\x02'\
'\x03\x04\x05\x06\x07\x08\x09\x0A\x0B\x01\x00\x03'\
'\x01\x01\x01\x01\x01\x01\x01\x01\x01\x00\x00\x00'\
'\x00\x00\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09'\
'\x0A\x0B\x10\x00\x02\x01\x03\x03\x02\x04\x03\x05'\
'\x05\x04\x04\x00\x00\x01\x7D\x01\x02\x03\x00\x04'\
'\x11\x05\x12\x21\x31\x41\x06\x13\x51\x61\x07\x22'\
'\x71\x14\x32\x81\x91\xA1\x08\x23\x42\xB1\xC1\x15'\
'\x52\xD1\xF0\x24\x33\x62\x72\x82\x09\x0A\x16\x17'\
'\x18\x19\x1A\x25\x26\x27\x28\x29\x2A\x34\x35\x36'\
'\x37\x38\x39\x3A\x43\x44\x45\x46\x47\x48\x49\x4A'\
'\x53\x54\x55\x56\x57\x58\x59\x5A\x63\x64\x65\x66'\
'\x67\x68\x69\x6A\x73\x74\x75\x76\x77\x78\x79\x7A'\
'\x83\x84\x85\x86\x87\x88\x89\x8A\x92\x93\x94\x95'\
'\x96\x97\x98\x99\x9A\xA2\xA3\xA4\xA5\xA6\xA7\xA8'\
'\xA9\xAA\xB2\xB3\xB4\xB5\xB6\xB7\xB8\xB9\xBA\xC2'\
'\xC3\xC4\xC5\xC6\xC7\xC8\xC9\xCA\xD2\xD3\xD4\xD5'\
'\xD6\xD7\xD8\xD9\xDA\xE1\xE2\xE3\xE4\xE5\xE6\xE7'\
'\xE8\xE9\xEA\xF1\xF2\xF3\xF4\xF5\xF6\xF7\xF8\xF9'\
'\xFA\x11\x00\x02\x01\x02\x04\x04\x03\x04\x07\x05'\
'\x04\x04\x00\x01\x02\x77\x00\x01\x02\x03\x11\x04'\
'\x05\x21\x31\x06\x12\x41\x51\x07\x61\x71\x13\x22'\
'\x32\x81\x08\x14\x42\x91\xA1\xB1\xC1\x09\x23\x33'\
'\x52\xF0\x15\x62\x72\xD1\x0A\x16\x24\x34\xE1\x25'\
'\xF1\x17\x18\x19\x1A\x26\x27\x28\x29\x2A\x35\x36'\
'\x37\x38\x39\x3A\x43\x44\x45\x46\x47\x48\x49\x4A'\
'\x53\x54\x55\x56\x57\x58\x59\x5A\x63\x64\x65\x66'\
'\x67\x68\x69\x6A\x73\x74\x75\x76\x77\x78\x79\x7A'\
'\x82\x83\x84\x85\x86\x87\x88\x89\x8A\x92\x93\x94'\
'\x95\x96\x97\x98\x99\x9A\xA2\xA3\xA4\xA5\xA6\xA7'\
'\xA8\xA9\xAA\xB2\xB3\xB4\xB5\xB6\xB7\xB8\xB9\xBA'\
'\xC2\xC3\xC4\xC5\xC6\xC7\xC8\xC9\xCA\xD2\xD3\xD4'\
'\xD5\xD6\xD7\xD8\xD9\xDA\xE2\xE3\xE4\xE5\xE6\xE7'\
'\xE8\xE9\xEA\xF2\xF3\xF4\xF5\xF6\xF7\xF8\xF9\xFA'
class ParseJpeg(object):
def __init__(self):
pass
def Open(self, fiHandle, verbose = 0):
#This function steps through the JPEG structure but
#does nothing useful. It might be a useful basis for
#extension.
data = fiHandle.read()
parsing = True
frameStartPos = 0
while parsing:
#Check if we should stop
if frameStartPos >= len(data):
parsing = False
continue
#Read the next segment
twoBytes, frameStartPos, frameEndPos = self.ReadFrame(data, frameStartPos)
if verbose:
print map(hex, twoBytes), frameStartPos, frameEndPos
#Move cursor
frameStartPos = frameEndPos
def InsertHuffmanTable(self, fiHandle, outHandle, verbose = 0):
#This converts an MJPEG frame into a standard JPEG binary
#MJPEG images omit the huffman table if the standard table
#is used. If it is missing, this function adds the table
#into the file structure.
data = fiHandle.read()
parsing = True
frameStartPos = 0
huffFound = False
while parsing:
#Check if we should stop
if frameStartPos >= len(data):
parsing = False
continue
#Read the next segment
twoBytes, frameStartPos, frameEndPos = self.ReadFrame(data, frameStartPos)
if verbose:
print map(hex, twoBytes), frameStartPos, frameEndPos
#Stop if there is a serious error
if frameStartPos is None:
parsing = False
continue
#Check if this segment is the compressed data
if twoBytes[0] == 0xff and twoBytes[1] == 0xda and not huffFound:
outHandle.write(huffmanSegment)
#Check the type of frame
if twoBytes[0] == 0xff and twoBytes[1] == 0xc4:
huffFound = True
#Write current structure to output
outHandle.write(data[frameStartPos:frameEndPos])
#Move cursor
frameStartPos = frameEndPos
def ReadFrame(self, data, offset):
#Based on http://www.gdcl.co.uk/2013/05/02/Motion-JPEG.html
#and https://en.wikipedia.org/wiki/JPEG
cursor = offset
#Check frame start
frameStartPos = offset
twoBytes = struct.unpack_from("BB", data, cursor)
if twoBytes[0] != 0xff:
print "Error: found header", map(hex,twoBytes),"at position",cursor
return twoBytes, None, None
#print map(hex, twoBytes)
cursor += 2
#Handle padding
paddingByte = twoBytes[0] == 0xff and twoBytes[1] == 0xff
if paddingByte: return twoBytes, frameStartPos, cursor
#Structure markers with 2 byte length
markHeader = twoBytes[0] == 0xff and twoBytes[1] >= 0xd0 and twoBytes[1] <= 0xd9
if markHeader: return twoBytes, frameStartPos, cursor
#Determine length of compressed (entropy) data
compressedDataStart = twoBytes[0] == 0xff and twoBytes[1] == 0xda
if compressedDataStart:
sosLength = struct.unpack_from(">H", data, cursor)[0]
cursor += sosLength
#Seek through frame
run = True
entropyData = ""
while run:
byteEnc = data[cursor]
byte = struct.unpack_from("B", data, cursor)[0]
cursor += 1
if byte == 0xff:
byte2 = struct.unpack_from("B", data, cursor)[0]
cursor += 1
if byte2 != 0x00:
if byte2 >= 0xd0 and byte2 <= 0xd8:
#Found restart structure
#print hex(byte), hex(byte2)
pass
else:
#End of frame
run = 0
cursor -= 2
else:
#Add escaped 0xff value in entropy data
entropyData += byteEnc
else:
entropyData += byteEnc
return twoBytes, frameStartPos, cursor
#More cursor for all other segment types
segLength = struct.unpack_from(">H", data, cursor)[0]
#print "segLength", segLength
cursor += segLength
return twoBytes, frameStartPos, cursor
if __name__ == "__main__":
pj = ParseJpeg()
pj.InsertHuffmanTable(open("test.mjpeg","rb"), open("test2.jpeg","wb"), verbose = 1)
#pj.InsertHuffmanTable(open("IMG_6618.JPG","rb"), open("IMG_6618b.JPG","wb"))
#pj.Open(open("IMG_6618.JPG","rb"), verbose = 1)
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