flv+h264 configuration tag mux和demux

flv+h264 configuration tag mux

函数ff_isom_write_avcc()

int ff_isom_write_avcc(AVIOContext *pb, const uint8_t *data, int len)
{
if (len > 6) {
/* check for H.264 start code */
if (AV_RB32(data) == 0x00000001 ||
AV_RB24(data) == 0x000001) {
uint8_t *buf=NULL, *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 (end - buf > 4) {
uint32_t size;
uint8_t nal_type;
size = FFMIN(AV_RB32(buf), end - buf - 4);
buf += 4;
nal_type = buf[0] & 0x1f;

if (nal_type == 7) { /* SPS */
sps = buf;
sps_size = size;
} else if (nal_type == 8) { /* PPS */
pps = buf;
pps_size = size;
}

buf += size;
}

if (!sps || !pps || sps_size < 4 || sps_size > UINT16_MAX || pps_size > UINT16_MAX)
return AVERROR_INVALIDDATA;

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);
av_free(start);
} else {
avio_write(pb, data, len);
}
}
return 0;
}

参见标准：

ISO/IEC 14496-15:2010

Information technology -- Coding of audio-visual objects -- Part 15: Advanced Video Coding (AVC) file format

flv+h264 HEVCDecoderConfigurationRecord tag demux

函数ff_h264_decode_extradata

int ff_h264_decode_extradata(const uint8_t *data, int size, H264ParamSets *ps,
int *is_avc, int *nal_length_size,
int err_recognition, void *logctx)
{
int ret;

if (!data || size <= 0)
return -1;

if (data[0] == 1) {
int i, cnt, nalsize;
const uint8_t *p = data;

*is_avc = 1;

if (size < 7) {
av_log(logctx, AV_LOG_ERROR, "avcC %d too short\n", size);
return AVERROR_INVALIDDATA;
}

// Decode sps from avcC
cnt = *(p + 5) & 0x1f; // Number of sps
p  += 6;
for (i = 0; i < cnt; i++) {
nalsize = AV_RB16(p) + 2;
if (nalsize > size - (p - data))
return AVERROR_INVALIDDATA;
ret = decode_extradata_ps_mp4(p, nalsize, ps, err_recognition, logctx);
if (ret < 0) {
av_log(logctx, AV_LOG_ERROR,
"Decoding sps %d from avcC failed\n", i);
return ret;
}
p += nalsize;
}
// Decode pps from avcC
cnt = *(p++); // Number of pps
for (i = 0; i < cnt; i++) {
nalsize = AV_RB16(p) + 2;
if (nalsize > size - (p - data))
return AVERROR_INVALIDDATA;
ret = decode_extradata_ps_mp4(p, nalsize, ps, err_recognition, logctx);
if (ret < 0) {
av_log(logctx, AV_LOG_ERROR,
"Decoding pps %d from avcC failed\n", i);
return ret;
}
p += nalsize;
}
// Store right nal length size that will be used to parse all other nals
*nal_length_size = (data[4] & 0x03) + 1;
} else {
*is_avc = 0;
ret = decode_extradata_ps(data, size, ps, 0, logctx);
if (ret < 0)
return ret;
}
return size;
}