从 ffmpeg 提取从 raw 到 CodecPrivate 的转换：
/*
* AVC helper functions for muxers
* Copyright (c) 2006 Baptiste Coudurier <baptiste.coudurier@smartjog.com>
* Modified by _Vi: stand-alone version (without ffmpeg)
*
* This file is based on the code from FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <string.h>
#include <stdio.h>
#define assert(x) if(!(x)) { fprintf(stderr, "Assertion failed...\n"); return -1; }
#ifndef AV_RB24
# define AV_RB24(x) \
((((const uint8_t*)(x))[0] << 16) | \
(((const uint8_t*)(x))[1] << 8) | \
((const uint8_t*)(x))[2])
#endif
#ifndef AV_RB32
# define AV_RB32(x) \
(((uint32_t)((const uint8_t*)(x))[0] << 24) | \
(((const uint8_t*)(x))[1] << 16) | \
(((const uint8_t*)(x))[2] << 8) | \
((const uint8_t*)(x))[3])
#endif
#define avio_w8(pb, x) *(*pb)++ = x;
#define avio_wb16(pb, x) *(*pb)++ = ((x)>>8); *(*pb)++ = x&0xFF;
#define avio_wb32(pb, x) *(*pb)++ = ((x)>>24); \
*(*pb)++ = ((x)>>16)&0xFF; \
*(*pb)++ = ((x)>>8)&0xFF; \
*(*pb)++ = ((x)>>0)&0xFF;
#define avio_write(pb, b, l) memcpy((*pb), b, l); (*pb)+=(l);
typedef unsigned char uint8_t;
typedef int intptr_t;
typedef unsigned long uint32_t;
static const uint8_t *ff_avc_find_startcode_internal(const uint8_t *p, const uint8_t *end)
{
const uint8_t *a = p + 4 - ((intptr_t)p & 3);
for (end -= 3; p < a && p < end; p++) {
if (p[0] == 0 && p[1] == 0 && p[2] == 1)
return p;
}
for (end -= 3; p < end; p += 4) {
uint32_t x = *(const uint32_t*)p;
// if ((x - 0x01000100) & (~x) & 0x80008000) // little endian
// if ((x - 0x00010001) & (~x) & 0x00800080) // big endian
if ((x - 0x01010101) & (~x) & 0x80808080) { // generic
if (p[1] == 0) {
if (p[0] == 0 && p[2] == 1)
return p;
if (p[2] == 0 && p[3] == 1)
return p+1;
}
if (p[3] == 0) {
if (p[2] == 0 && p[4] == 1)
return p+2;
if (p[4] == 0 && p[5] == 1)
return p+3;
}
}
}
for (end += 3; p < end; p++) {
if (p[0] == 0 && p[1] == 0 && p[2] == 1)
return p;
}
return end + 3;
}
const uint8_t *ff_avc_find_startcode(const uint8_t *p, const uint8_t *end){
const uint8_t *out= ff_avc_find_startcode_internal(p, end);
if(p<out && out<end && !out[-1]) out--;
return out;
}
int ff_avc_parse_nal_units(unsigned char **pb, const uint8_t *buf_in, int size)
{
const uint8_t *p = buf_in;
const uint8_t *end = p + size;
const uint8_t *nal_start, *nal_end;
size = 0;
nal_start = ff_avc_find_startcode(p, end);
while (nal_start < end) {
while(!*(nal_start++));
nal_end = ff_avc_find_startcode(nal_start, end);
avio_wb32(pb, nal_end - nal_start);
avio_write(pb, nal_start, nal_end - nal_start);
size += 4 + nal_end - nal_start;
nal_start = nal_end;
}
return size;
}
int ff_avc_parse_nal_units_buf(const unsigned char *buf_in, unsigned char **buf, int *size)
{
unsigned char *pbptr = *buf;
ff_avc_parse_nal_units(&pbptr, buf_in, *size);
*size = pbptr - *buf;
return 0;
}
int my_isom_write_avcc(unsigned char **pb, const uint8_t *data, int len)
{
unsigned char tmpbuf[4000];
if (len > 6) {
/* check for h264 start code */
if (AV_RB32(data) == 0x00000001 ||
AV_RB24(data) == 0x000001) {
uint8_t *buf=tmpbuf, *end, *start;
uint32_t sps_size=0, pps_size=0;
uint8_t *sps=0, *pps=0;
int ret = ff_avc_parse_nal_units_buf(data, &buf, &len);
if (ret < 0)
return ret;
start = buf;
end = buf + len;
/* look for sps and pps */
while (buf < end) {
unsigned int size;
uint8_t nal_type;
size = AV_RB32(buf);
nal_type = buf[4] & 0x1f;
if (nal_type == 7) { /* SPS */
sps = buf + 4;
sps_size = size;
} else if (nal_type == 8) { /* PPS */
pps = buf + 4;
pps_size = size;
}
buf += size + 4;
}
assert(sps);
assert(pps);
avio_w8(pb, 1); /* version */
avio_w8(pb, sps[1]); /* profile */
avio_w8(pb, sps[2]); /* profile compat */
avio_w8(pb, sps[3]); /* level */
avio_w8(pb, 0xff); /* 6 bits reserved (111111) + 2 bits nal size length - 1 (11) */
avio_w8(pb, 0xe1); /* 3 bits reserved (111) + 5 bits number of sps (00001) */
avio_wb16(pb, sps_size);
avio_write(pb, sps, sps_size);
avio_w8(pb, 1); /* number of pps */
avio_wb16(pb, pps_size);
avio_write(pb, pps, pps_size);
} else {
avio_write(pb, data, len);
}
}
return 0;
}
#define H264PRIVATE_MAIN
#ifdef H264PRIVATE_MAIN
int main() {
unsigned char data[1000];
int len = fread(data, 1, 1000, stdin);
unsigned char output[1000];
unsigned char *output_f = output;
my_isom_write_avcc(&output_f, data, len);
fwrite(output, 1, output_f - output, stdout);
return 0;
}
#endif
在每个 base-64 解码块之前插入“00 00 00 01”并将其输入该程序输出 CodecPrivate：
$ printf '\x00\x00\x00\x01'\
'\x67\x42\xc0\x14\xda\x05\x07\xe8\x40\x00\x00\x03\x00\x40\x00\x00\x0c\x03\xc5\x0a\xa8'\
'\x00\x00\x00\x01'\
'\x68\xce\x0f\xc8' | ./avc_to_mkvcodecpriv | hd
00000000 01 42 c0 14 ff e1 00 15 67 42 c0 14 da 05 07 e8 |.B......gB......|
00000010 40 00 00 03 00 40 00 00 0c 03 c5 0a a8 01 00 04 |@....@..........|
00000020 68 ce 0f c8 |h...|
00000024