LAME 编码器将音频流的 CRC16 校验和存储在其编码的每个 MP3 的标头中。然后可以计算“实际”音频校验和，并在以后将其与原始值进行比较，以验证音频是否已损坏（无需担心 ID3 标签等会更改计算值）。
在 Windows 上，有一个名为 LameTag 的命令行实用程序，它能够计算校验和并将其与原始校验和进行比较。不幸的是，它已被废弃，并且可能不易移植到 OS X，而我使用的当然是 OS X。我认为 EncSpot 能够做同样的事情，但它同样仅适用于 Windows。
我的问题是：是否有任何类似的实用程序与 Mac、Linux、BSD 或类似系统兼容？
我发现有一些可以显示原来的CRC（如eyeD3），但它们无法计算当前值。还有几个实用程序声称可以检查 MP3 中的损坏情况，但我没有发现任何实际使用 MusicCRC 框架的实用程序 — 它们中的大多数似乎使用更通用的检查方法，或者它们使用框架 CRC（默认情况下在 LAME 中禁用，不能依赖）。
编辑：
我想我已经回答了自己的问题。在研究这个问题的过程中，我偶然发现了Python 脚本为了诱变剂，QuodLibet 的音频元数据库。该脚本旨在读取 LAME 的信息标签，虽然它没有专门处理 CRC 字段，但我能够根据其示例创建一些可以处理的内容。经过几个小时的折腾（我是一个糟糕的程序员，对 Python 一无所知），我终于设法编写了一些东西，虽然没有特色而且很慢，但确实返回了原始 CRC和计算新的：
# Known good track
kapche-lanka:test % ../mp3crc.py "10 - CLAW FINGER.mp3"
10 - CLAW FINGER.mp3:
Original MusicCRC: 8171
Computed MusicCRC: 8171
Original Info Tag CRC: AEFD
Computed Info Tag CRC: AEFD
# Known bad track
kapche-lanka:test % ../mp3crc.py "10 - Griffons Never Die.mp3"
10 - Griffons Never Die.mp3:
Original MusicCRC: 2014
Computed MusicCRC: BCF1
Original Info Tag CRC: DF02
Computed Info Tag CRC: DF02
每当我以更严肃的方式使其工作时，我将再次更新此帖子以添加指向脚本的链接。
谢谢！
编辑2：
我在下面添加了一个指向我的脚本的链接（请参阅已接受的答案）。它被称为mp3crc，虽然设计得不是专业，但似乎在大多数情况下都有效：
答案1
下面是一个 Bash shell 函数，lameCRC()用于计算 Xing/Info-LAME 头帧的 LAME musicCRC 和 CRC-16（由Mp3 信息标签修订版 1 规范 - 草稿 0）通过使用 Apple 的afinfo命令和crcHampa Hug 的命令行工具，http://www.hampa.ch/misc-utils/index.html。
如果 Apple 的afinfo命令不可用，dd则会使用它（但这会导致速度减慢）。
（注意：我故意避免使用 Bash 的内部字符串函数，以使可移植性更容易）。
lameCRC() { # Bash shell function
# lameCRC() uses the crc command line tool from http://www.hampa.ch/misc-utils/index.html.
# lameCRC() is partly inspired by the output of Apple's afinfo command and
# the C source code of Audio-Scan-0.93 and MP3-Cut-Gapless-0.03 by Andy Grundman:
# https://metacpan.org/author/AGRUNDMA
# Audio-Scan-0.93/src/mp3.c (GNU General Public License Version 2, June 1991 or later)
# Audio-Scan-0.93/include/mp3.h ( ditto )
# MP3-Cut-Gapless-0.03/src/mp3cut.c ( ditto )
# usage: lameCRC lame.mp3
# Basic information:
# Mp3 Info Tag rev 1 specifications, http://gabriel.mp3-tech.org/mp3infotag.html
# LAME info header zone A has a length of 120 bytes (or 240 chars in xxd hex output).
# The "LAMEx." string is followed by 30 bytes (or 60 chars in xxd hex output) according to the
# "Suggested Info Tag extension fields + layout" in the Mp3 Info Tag rev 1 specifications.
local n n1 n2 lines plus crcs hexchar lame_start_idx xinginfo_start_idx PATH
PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
[[ ! -x '/usr/local/bin/crc' ]] &&
{ printf '%s\n' 'No crc command line tool in /usr/local/bin!' 'See: http://www.hampa.ch/misc-utils/index.html' 1>&2; }
# get Xing|Info|LAME strings and their offsets in binary file
lines="$(strings -a -n 4 -t d "$1" | grep -E --line-buffered 'Xing|Info|LAME.\.' | head -n 2)"
[[ $(echo "$lines" | grep -E -c 'Xing|Info') -ne 1 ]] ||
[[ $(echo "$lines" | grep -E -c 'LAME[^ ]{5}') -ne 1 ]] && {
echo 'No Xing|Info string or correct LAME encoder version string (e.g. LAME3.98r) found!' 1>&2;
echo "$lines" 1>&2;
return 1;
}
# get offset index numbers of Xing|Info|LAME strings
lame_start_idx="$(printf '%s' "$lines" | awk '/LAME/{print $1}' )"
xinginfo_start_idx="$(printf '%s' "$lines" | awk '/Xing|Info/{print $1}' )"
# get possible offset of LAME string in output of strings command
# LAME version string should consist of 9 chars, but may have a prefix in output of strings command
# example: 9LAME3.98r instead of LAME3.98r
# example: 7LAME3.88 (beta) instead of LAME3.88 (beta)
#plus="$(printf '%s' "$lines" | sed -n 's/^[^ ]*[ ][ ]*\([^ ]*\)LAME[^ ]\{5\}.*/\1/p' | tr -d '\n' | wc -c)" # use [^ ]\{5\} ?
plus="$(printf '%s' "$lines" | sed -n 's/^[^ ]*[ ][ ]*\([^ ]*\)LAME.*/\1/p' | tr -d '\n' | wc -c)"
lame_start_idx=$(( $lame_start_idx + $plus ))
[[ $(( $lame_start_idx - $xinginfo_start_idx )) -ne 120 ]] &&
{ echo 'No 120 bytes between Xing / Info and LAME string. Exiting ...' 1>&2; return 1; }
# get entire LAME info tag
#dd if="$1" bs=1 skip="$lame_start_idx" count=36 2>/dev/null | LC_ALL=C od -A n -cv; return 0
# get bytes $BC-$BD (MusicCRC) and bytes $BE-$BF (CRC-16 of Info Tag) (as described in http://gabriel.mp3-tech.org/mp3infotag.html)
crcs="$(dd if="$1" bs=1 skip="$(( $lame_start_idx + 32 ))" count=4 2>/dev/null | xxd -p | tr -d '\n')"
[[ -z "$crcs" ]] && { echo 'No LAME musicCRC and CRC-16 of Info Tag found!' 1>&2; return 1; }
lameMusicLengthPlusCRCs="$(dd if="$1" bs=1 skip=$(( $lame_start_idx + 28 )) count=8 2>/dev/null | xxd -p | tr -d '\n')"
lameMusicLength="$(echo "$lameMusicLengthPlusCRCs" | cut -b 1-8 )"
lameMusicCRC1="$(echo "$lameMusicLengthPlusCRCs" | cut -b 9-10 )" # cf. http://gabriel.mp3-tech.org/mp3infotag#musiccrc
lameMusicCRC2="$(echo "$lameMusicLengthPlusCRCs" | cut -b 11-12 )"
lameInfoTagCRC16="$(echo "$lameMusicLengthPlusCRCs" | cut -b 13-16 )"
# LAME MusicLength consists of:
# [LAME Tag frame][complete mp3 music data]
lameMusicLengthByteSize=$(printf '%d' "0x${lameMusicLength}")
[[ $lameMusicLengthByteSize -le 0 ]] && { echo 'lameMusicLengthByteSize <= 0. Exiting ...' 1>&2; return 1; }
if [[ -x '/usr/bin/sw_vers' ]] && [[ "$(/usr/bin/sw_vers -productName)" == "Mac OS X" ]] && [[ -x '/usr/bin/afinfo' ]]; then
# get audio_bytes, i. e. [complete mp3 music data] - [LAME Tag frame]
#id3v2 --delete-all "$1" 1>/dev/null # for testing purposes; edits file in-place!
# afinfo seems to be only available on Mac OS X
# afinfo alternative: Perl module Audio-Scan-0.93 by Andy Grundman
# perl -e 'use Audio::Scan; my $offset = Audio::Scan->find_frame($ARGV[1],0); print "$offset\n";' _ file.mp3
audioinfo="$(afinfo "$1")"
audio_bytes="$(echo "$audioinfo" | awk -F" " '/audio bytes:/{print $NF}' )"
audio_data_file_offset="$(echo "$audioinfo" | awk -F" " '/audio data file offset:/{print $NF}')"
xingInfoLameTagFrameSize=$(( lameMusicLengthByteSize - audio_bytes ))
[[ $audio_bytes -le 0 ]] && { echo 'audio_bytes <= 0. Exiting ...' 1>&2; return 1; }
# 0..xingInfoLameTagFrameOffset (match first 0xff byte in mp3 file)
n=0
hexchar=""
until [[ "$hexchar" == 'ff' ]]; do
hexchar="$(dd if="$1" bs=1 skip=$n count=1 2>/dev/null | xxd -p)"
n=$(( n + 1))
done
xingInfoLameTagFrameOffset=$(( n - 1 ))
else # dd speed bump
# get xingInfoLameTagFrameSize
# for mp3 magic numbers (\xFF\xFB) see:
# http://www.digitalpreservation.gov/formats/fdd/fdd000105.shtml
# n1
# count bytes from: 0xff...<--...$xinginfo_start_idx
hexchar=""
n=$xinginfo_start_idx
until [[ "$hexchar" == 'ff' ]]; do
n=$(( n - 1))
hexchar="$(dd if="$1" bs=1 skip=$n count=1 2>/dev/null | xxd -p)"
done
xingInfoLameTagFrameOffset=$n
n1=$(( xinginfo_start_idx - n ))
# n2
# count bytes from: $xinginfo_start_idx+120+36...-->...0xff
hexchar=""
n=$((xinginfo_start_idx + 120 + 36))
until [[ "$hexchar" == 'ff' ]]; do
hexchar="$(dd if="$1" bs=1 skip=$n count=1 2>/dev/null | xxd -p)"
n=$(( n + 1))
done
n2=$(( n - xinginfo_start_idx - 120 - 36 - 1 )) # - 1 because the trailing 0xff got counted by $n
xingInfoLameTagFrameSize=$(( $n1 + $n2 + 120 + 36 ))
audio_data_file_offset=$((xingInfoLameTagFrameOffset + xingInfoLameTagFrameSize))
# get audio_bytes, i. e. [complete mp3 music data] - [LAME Tag frame]
audio_bytes=$( printf "%s\n" "scale = 0; ${lameMusicLengthByteSize} - ${xingInfoLameTagFrameSize}" | bc )
fi
old_lameInfoTagCRC16="$lameInfoTagCRC16"
new_lameInfoTagCRC16="$(head -c $(( xingInfoLameTagFrameOffset + xingInfoLameTagFrameSize )) "$1" |
tail -c ${xingInfoLameTagFrameSize} | head -c 190 | crc -R -r -g crc16)"
old_lameMusicCRC16="${lameMusicCRC1}${lameMusicCRC2}"
new_lameMusicCRC16="$(head -c $(( ${audio_data_file_offset} + ${audio_bytes} )) "$1" |
tail -c ${audio_bytes} | crc -R -r -g crc16)"
echo
printf '%s\n' "old_lameInfoTagCRC16: ${old_lameInfoTagCRC16}" "new_lameInfoTagCRC16: ${new_lameInfoTagCRC16}"
echo
printf '%s\n' "old_lameMusicCRC16: ${old_lameMusicCRC16}" "new_lameMusicCRC16: ${new_lameMusicCRC16}"
echo
return 0
}
答案2
似乎有一个 C 端口LameTag_Source_0.4.1/CRC16.pas称为mp3_check-1.98/crctest.c（这是一个命令行工具）。
这是一个破解版本mp3_check-1.98/crctest.c，可以计算给定 mp3 文件的 CRC16 校验和。
/*
modified version of source code taken from:
mp3_check-1.98/crctest.c,
http://sourceforge.net/projects/mp3check/
NOTE:
compare mp3_check-1.98/crctest.c with
LameTag_Source_0.4.1/CRC16.pas from
http://phwip.wordpress.com/home/audio/
See also:
mp3check - check mp3 files for integrity,
http://jo.ath.cx/soft/mp3check/
gcc -Wall -Wextra -03 -o crctest crctest.c
./crctest *.mp3
printf '%d\n' $(./crctest *.mp3)
*/
#include <stdio.h>
#include <stdlib.h>
int
crcbuf(crc, len, buf)
register int crc; /* running CRC value */
register unsigned long len;
register char *buf;
{
static short crc_table[] = {
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};
register unsigned long i;
for (i=0; i<len; i++)
crc = ((crc >> 8) & 0xff) ^ crc_table[(crc ^ *buf++) & 0xff];
return (crc);
}
int main (int argc, char * argv [])
{
if (argc != 2) return(1);
int crc = 0;
int newcrc = 0;
// cf. http://www.linuxquestions.org/questions/programming-9/c-howto-read-binary-file-into-buffer-172985/
char *name = argv[1];
FILE *file;
char *buffer;
unsigned long fileLen;
//Open file
file = fopen(name, "rb");
if (!file)
{
fprintf(stderr, "Unable to open file %s", name);
return(1);
}
//Get file length
fseek(file, 0, SEEK_END);
fileLen=ftell(file);
fseek(file, 0, SEEK_SET);
//Allocate memory
buffer=(char *)malloc(fileLen+1);
if (!buffer)
{
fprintf(stderr, "Memory error!");
fclose(file);
return(1);
}
//Read file contents into buffer
fread(buffer, fileLen, 1, file);
fclose(file);
newcrc = crcbuf(crc, fileLen, buffer);
printf("0x%x\n", newcrc);
free(buffer);
return(0);
}
答案3
我将在这里回答我自己的问题：
在尝试研究这个问题时，我偶然发现了Python 脚本为了mutagen，QuodLibet 的音频元数据库。该脚本旨在读取 LAME 的信息标签，尽管它不专门处理 CRC 字段，但我能够根据其示例创建一些可以处理的内容。经过几个小时的折腾（我是一个糟糕的程序员，对 Python 一无所知），我终于设法编写了一些东西，虽然没有特色而且很慢，但确实返回原始 CRC 并计算新的 CRC。它仍然有点问题，但在我自己的库中，它的准确率至少达到 90%，所以我猜我会“发布”它。它的名字是mp3crcGitHub，可在以下位置找到：
https://github.com/ohkine/mp3crc
该脚本应在 UNIX 和 Windows 上运行，尽管目前有一个仅适用于 Windows 的 Unicode 问题需要修复。它还需要安装crcmod和（我将它们包含在存储库中，但您可以自行安装它们）。mutagen
如上所述，我不是一个很好的程序员，所以我提前为代码可能有多尴尬道歉。但它基本上有效 :)