Converting between SDP's sprop-parameter-sets and mkv's CodecPrivate

StackOverflow https://stackoverflow.com/questions/16159305

Question

Is there some easy way to convert between h264 settings as stored in Matroska file:

+ CodecPrivate, length 36 (h.264 profile: Baseline @L2.0) hexdump 
01 42 c0 14 ff e1 00 15 67 42 c0 14 da 05 07 e8
40 00 00 03 00 40 00 00 0c 03 c5 0a a8 01 00 04
68 ce 0f c8

and the same settings when streaming that matroska file using RTSP?:

a=fmtp:96 packetization-mode=1;profile-level-id=42C014;sprop-parameter-sets=Z0LAFNoFB+hAAAADAEAAAAwDxQqo,aM4PyA==

Base-64 strings decodes to this:

00000000  67 42 c0 14 da 05 07 e8  40 00 00 03 00 40 00 00  |gB......@....@..|
00000010  0c 03 c5 0a a8    

00000000  68 ce 0f c8                                       |h...|

which partially matches the data in mkv's CodecPrivate.

Was it helpful?

Solution

Extracted conversion from raw to CodecPrivate from ffmpeg:

/*
 * 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

Inserting "00 00 00 01" before each base-64-decoded block and feeding it into that program outputs 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
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