英文:
Formation of CRC-32 for SDT to ts. file
问题
我的任务是从服务器捕获视频流并将其写入ts文件。当我尝试将SDT包写入ts文件时，遇到了一个问题。我通过字节手动形成数据包，但是我无法计算SDT末尾的4个字节的CRC-32校验和。（使用golang）
我尝试根据已写入SDT包的数据的校验和来获取CRC，但是它不起作用。在逐字节解析的SDT中，CRC与我计算的不同。
英文:
My task is to capture the videostream from the server and write it to ts. files. I ran into a problem when trying to write a SDT package to ts. I form the packet manually by bytes and I can’t figure out how to calculate 4 bytes of CRC-32 for the end of SDT. (used golang)
I tried to get the CRC based on the checksum of the data already written to the SDT packet, but it doesn't work. In the byte-by-byte parsed SDT, CRC was different from what I calculated.
答案1
得分: 2
如果你在谈论MPEG-2，那么CRC的定义如下：
width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 residue=0x00000000 name="CRC-32/MPEG-2"
在RFC 4326中有一个例子：
00 3f 86 dd 00 01 02 03 04 05 60 00 00 00 00 0d
3a 40 20 01 0d b8 30 08 19 65 00 00 00 00 00 00
00 01 20 01 0d b8 25 09 19 62 00 00 00 00 00 00
00 02 80 00 9d 8c 06 38 00 04 00 00 00 00 00 7c
17 17 63
其中最后四个字节是它之前所有字节的CRC-32/MPEG-2（按大端顺序）。
以下是计算该CRC的示例C代码：
#include <stddef.h>
#include <stdint.h>
uint32_t crc32mpeg2(uint32_t crc, void const *mem, size_t len) {
unsigned char const *data = mem;
if (data == NULL)
return 0xffffffff;
for (size_t i = 0; i < len; i++) {
crc ^= (uint32_t)data[i] << 24;
for (unsigned k = 0; k < 8; k++) {
crc = crc & 0x80000000 ? (crc << 1) ^ 0x4c11db7 : crc << 1;
}
}
return crc;
}
（当mem等于NULL时，返回初始CRC值。）
英文:
If you're talking about MPEG-2, then the CRC definition is:
width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 residue=0x00000000 name="CRC-32/MPEG-2"
There is an example in RFC 4326:
00 3f 86 dd 00 01 02 03 04 05 60 00 00 00 00 0d
3a 40 20 01 0d b8 30 08 19 65 00 00 00 00 00 00
00 01 20 01 0d b8 25 09 19 62 00 00 00 00 00 00
00 02 80 00 9d 8c 06 38 00 04 00 00 00 00 00 7c
17 17 63
where the last four bytes of that is the CRC-32/MPEG-2 (in big-endian order) of all of the bytes that precede it.
Here is example C code to calculate that CRC:
#include <stddef.h>
#include <stdint.h>
uint32_t crc32mpeg2(uint32_t crc, void const *mem, size_t len) {
unsigned char const *data = mem;
if (data == NULL)
return 0xffffffff;
for (size_t i = 0; i < len; i++) {
crc ^= (uint32_t)data[i] << 24;
for (unsigned k = 0; k < 8; k++) {
crc = crc & 0x80000000 ? (crc << 1) ^ 0x4c11db7 : crc << 1;
}
}
return crc;
}
(When called with mem equal to NULL, the initial CRC value is returned.)
答案2
得分: 2
以下是Mark Adler提供的相同（Golang）代码（如果有人需要）：
func CalcCRC32(data []byte) uint32 {
var crc uint32 = 0xffffffff
if data == nil {
return crc
}
for _, v := range data {
crc ^= uint32(v) << 24
for j := 0; j < 8; j++ {
if (crc & 0x80000000) != 0 {
crc = (crc << 1) ^ 0x04C11DB7
} else {
crc <<= 1
}
}
}
return crc
}
英文:
Here is the same (Golang) code as provided by Mark Adler (in case anyone needs it):
func CalcCRC32(data []byte) uint32 {
var crc uint32 = 0xffffffff
if data == nil {
return crc
}
for _, v := range data {
crc ^= uint32(v) << 24
for j := 0; j < 8; j++ {
if (crc & 0x80000000) != 0 {
crc = (crc << 1) ^ 0x04C11DB7
} else {
crc <<= 1
}
}
}
return crc
}
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