| 1 | from mmpython import mediainfo |
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| 2 | import mmpython |
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| 3 | |
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| 4 | import struct |
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| 5 | |
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| 6 | # http://www.atsc.org/standards/a_52a.pdf |
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| 7 | # fscod: Sample rate code, 2 bits |
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| 8 | # 00 48 |
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| 9 | # 01 44.1 |
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| 10 | # 10 32 |
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| 11 | # 11 reserved |
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| 12 | |
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| 13 | FSCOD = [ 48000, 44100, 32000, 0 ] |
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| 14 | |
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| 15 | # bsmod: Bit stream mode, 3 bits |
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| 16 | # bsmod acmod Type of Service |
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| 17 | # 000 any main audio service: complete main (CM) |
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| 18 | # 001 any main audio service: music and effects (ME) |
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| 19 | # 010 any associated service: visually impaired (VI) |
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| 20 | # 011 any associated service: hearing impaired (HI) |
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| 21 | # 100 any associated service: dialogue (D) |
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| 22 | # 101 any associated service: commentary (C) |
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| 23 | # 110 any associated service: emergency (E) |
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| 24 | # 111 001 associated service: voice over (VO) |
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| 25 | # 111 010 - 111 main audio service: karaoke |
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| 26 | # |
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| 27 | # acmod: Audio coding mode, 3 bits |
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| 28 | # 000 1+1 2 Ch1, Ch2 |
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| 29 | # 001 1/0 1 C |
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| 30 | # 010 2/0 2 L, R |
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| 31 | # 011 3/0 3 L, C, R |
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| 32 | # 100 2/1 3 L, R, S |
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| 33 | # 101 3/1 4 L, C, R, S |
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| 34 | # 110 2/2 4 L, R, SL, SR |
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| 35 | # 111 3/2 5 L, C, R, SL, SR |
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| 36 | |
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| 37 | ACMOD = [ ( '1+1', 2, 'Ch1, Ch2' ), |
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| 38 | ( '1/0', 1, 'C' ), |
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| 39 | ( '2/0', 2, 'L, R' ), |
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| 40 | ( '3/0', 3, 'L, C, R' ), |
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| 41 | ( '2/1', 3, 'L, R, S' ), |
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| 42 | ( '3/1', 4, 'L, C, R, S' ), |
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| 43 | ( '2/2', 4, 'L, R, SL, SR' ), |
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| 44 | ( '3/2', 5, 'L, C, R, SL, SR' ) ] |
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| 45 | |
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| 46 | |
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| 47 | # dsurmod: Dolby surround mode, 2 bits |
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| 48 | # 00 not indicated |
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| 49 | # 01 Not Dolby Surround encoded |
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| 50 | # 10 Dolby Surround encoded |
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| 51 | # 11 reserved |
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| 52 | # |
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| 53 | # lfeon: Low frequency effects channel on, 1 bit |
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| 54 | # This bit has a value of 1 if the lfe (sub woofer) channel is on, and a |
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| 55 | # value of 0 if the lfe channel is off. |
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| 56 | # |
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| 57 | # frmsizcod: |
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| 58 | # byte&0x3e = 0x00 \b, 32 kbit/s |
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| 59 | # byte&0x3e = 0x02 \b, 40 kbit/s |
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| 60 | # byte&0x3e = 0x04 \b, 48 kbit/s |
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| 61 | # byte&0x3e = 0x06 \b, 56 kbit/s |
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| 62 | # byte&0x3e = 0x08 \b, 64 kbit/s |
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| 63 | # byte&0x3e = 0x0a \b, 80 kbit/s |
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| 64 | # byte&0x3e = 0x0c \b, 96 kbit/s |
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| 65 | # byte&0x3e = 0x0e \b, 112 kbit/s |
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| 66 | # byte&0x3e = 0x10 \b, 128 kbit/s |
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| 67 | # byte&0x3e = 0x12 \b, 160 kbit/s |
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| 68 | # byte&0x3e = 0x14 \b, 192 kbit/s |
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| 69 | # byte&0x3e = 0x16 \b, 224 kbit/s |
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| 70 | # byte&0x3e = 0x18 \b, 256 kbit/s |
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| 71 | # byte&0x3e = 0x1a \b, 320 kbit/s |
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| 72 | # byte&0x3e = 0x1c \b, 384 kbit/s |
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| 73 | # byte&0x3e = 0x1e \b, 448 kbit/s |
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| 74 | # byte&0x3e = 0x20 \b, 512 kbit/s |
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| 75 | # byte&0x3e = 0x22 \b, 576 kbit/s |
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| 76 | # byte&0x3e = 0x24 \b, 640 kbit/s |
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| 77 | |
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| 78 | FRMSIZCOD = [ 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, |
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| 79 | 224, 256, 320, 384, 448, 512, 576, 640 ] |
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| 80 | |
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| 81 | class AC3Info(mediainfo.MusicInfo): |
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| 82 | def __init__(self,file): |
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| 83 | mediainfo.MusicInfo.__init__(self) |
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| 84 | if file.name.endswith('.ac3'): |
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| 85 | # when the ending is ac3, force the detection. It may not be necessary |
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| 86 | # the the header is at the beginning but in the first 2000 bytes |
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| 87 | check_length = 1000 |
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| 88 | else: |
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| 89 | check_length = 1 |
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| 90 | for i in range(check_length): |
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| 91 | if file.read(2) == '\x0b\x77': |
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| 92 | break |
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| 93 | else: |
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| 94 | self.valid = False |
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| 95 | return |
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| 96 | |
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| 97 | info = struct.unpack('<HBBBB',file.read(6)) |
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| 98 | self.samplerate = FSCOD[info[1] >> 6] |
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| 99 | self.bitrate = FRMSIZCOD[(info[1] & 0x3F) >> 1] * 1000 |
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| 100 | bsmod = info[2] & 0x7 |
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| 101 | channels = ACMOD[info[3] >> 5] |
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| 102 | acmod = info[3] >> 5 |
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| 103 | self.channels = ACMOD[acmod][1] |
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| 104 | bits = 0 |
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| 105 | if acmod & 0x01 and not acmod == 0x01: |
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| 106 | bits += 2 |
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| 107 | if acmod & 0x04: |
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| 108 | bits += 2 |
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| 109 | if acmod == 0x02: |
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| 110 | bits += 2 |
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| 111 | |
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| 112 | # info is now 5 bits of info[3] and all bits of info[4] ( == 13 bits) |
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| 113 | # 'bits' bits (0-6) bits are information we don't need, after that, |
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| 114 | # the bit we need is lfeon. |
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| 115 | info = (((info[3] & 0x1F) << 8) + info[4]) |
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| 116 | |
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| 117 | # now we create the mask we need (based on 'bits') |
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| 118 | # the bit number 13 - 'bits' is what we want to read |
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| 119 | for i in range(13 - bits - 1): |
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| 120 | info = info >> 1 |
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| 121 | if info & 1: |
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| 122 | # subwover |
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| 123 | self.channels += 1 |
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| 124 | self.valid = True |
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| 125 | self.codec = 'AC3' |
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| 126 | self.mime = 'audio/ac3' |
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| 127 | |
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| 128 | mmpython.registertype( 'audio/ac3', ('ac3',), mediainfo.TYPE_MUSIC, AC3Info ) |
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