H265封装成RTP流（二）
H265封装成RTP流（二）
H265封装成RTP流主要参考的文档为《draft-ietf-payload-rtp-h265-07.pdf》，在这个文档里面的第四章里进行了详细的说明。H265封装成RTP包，主要有四种模式：
1、单独一个NAL单元包打成RTP
2、多个NAL单元打成一个RTP包
3、一个NAL单元打成多个RTP包
4、PACI包
根据H264的打包方式和ffmpeg的内容，我们只有第一种和第三种，因为网的MTU大小的1500个字节，这里选择1400个字节为一个RTP包，如果一个NAL单元小于等于1400字节，则使用单独一个NAL单元包打成RTP，如果大于1400个字节，则使用一个NAL单元打成多个RTP包（FU），具体FU的代码如下红色的部分：
static void nal_send(AVFormatContext *s1, const uint8_t *buf, int size, int last)
{
RTPMuxContext *s = s1->priv_data;
enum AVCodecID codec = s1->streams[0]->codec->codec_id;
av_log(s1, AV_LOG_DEBUG, "Sending NAL %x of len %d M=%d\n", buf[0] & 0x1F, size, last);
if (size <= s->max_payload_size) {
int buffered_size = s->buf_ptr - s->buf;
int header_size;
int skip_aggregate = 0;
if (codec == AV_CODEC_ID_H264) {
header_size = 1;
skip_aggregate = s->flags & FF_RTP_FLAG_H264_MODE0;
}
else
{
header_size = 2;
}
// Flush buffered NAL units if the current unit doesn't fit
if (buffered_size + 2 + size > s->max_payload_size) {
flush_buffered(s1, 0);
buffered_size = 0;
}
// If we aren't using mode 0, and the NAL unit fits including the
// framing (2 bytes length, plus 1/2 bytes for the STAP-A/AP marker),
// write the unit to the buffer as a STAP-A/AP packet, otherwise flush
// and send as single NAL.
/*我们不使用模式0，这NAL单元适合包括帧（长度2字节，AP包）否则发送单个NAL包*/
if (buffered_size + 2 + header_size + size <= s->max_payload_size &&
!skip_aggregate) {
if (buffered_size == 0) {
if (codec == AV_CODEC_ID_H264) {
*s->buf_ptr++ = 24;
} else {
*s->buf_ptr++ = 48 << 1;
*s->buf_ptr++ = 1;
}
}
AV_WB16(s->buf_ptr, size);
s->buf_ptr += 2;
memcpy(s->buf_ptr, buf, size);
s->buf_ptr += size;
s->buffered_nals++;
} else {
flush_buffered(s1, 0);
ff_rtp_send_data(s1, buf, size, last);
}
} else {
int flag_byte, header_size;
flush_buffered(s1, 0);
if (codec == AV_CODEC_ID_H264 && (s->flags & FF_RTP_FLAG_H264_MODE0)) {
av_log(s1, AV_LOG_ERROR,
"NAL size %d > %d, try -slice-max-size %d\n", size,
s->max_payload_size, s->max_payload_size);
return;
}
av_log(s1, AV_LOG_DEBUG, "NAL size %d > %d\n", size, s->max_payload_size);
if (codec == AV_CODEC_ID_H264) {
uint8_t type = buf[0] & 0x1F;
uint8_t nri = buf[0] & 0x60;
s->buf[0] = 28; /* FU Indicator; Type = 28 ---> FU-A */
s->buf[0] |= nri;
s->buf[1] = type;
s->buf[1] |= 1 << 7;
buf += 1;
size -= 1;
flag_byte = 1;
header_size = 2;
} else {
uint8_t nal_type = (buf[0] >> 1) & 0x3F;
/*
* create the HEVC payload header and transmit the buffer as fragmentation units (FU)
*
* 0 1
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |F| Type | LayerId | TID |
* +-------------+-----------------+
*
* F = 0
* Type = 49 (fragmentation unit (FU))
* LayerId = 0
* TID = 1
*/
s->buf[0] = 49 << 1;
s->buf[1] = 1;
/*
* create the FU header
*
* 0 1 2 3 4 5 6 7
* +-+-+-+-+-+-+-+-+
* |S|E| FuType |
* +---------------+
*
* S = variable
* E = variable
* FuType = NAL unit type
*/
s->buf[2] = nal_type;
/* set the S bit: mark as start fragment */
s->buf[2] |= 1 << 7;
/* pass the original NAL header */
buf += 2;
size -= 2;
flag_byte = 2;
header_size = 3;
}
while (size + header_size > s->max_payload_size) {
memcpy(&s->buf[header_size], buf, s->max_payload_size - header_size);
ff_rtp_send_data(s1, s->buf, s->max_payload_size, 0);
buf += s->max_payload_size - header_size;
size -= s->max_payload_size - header_size;
s->buf[flag_byte] &= ~(1 << 7);
}
s->buf[flag_byte] |= 1 << 6;
memcpy(&s->buf[header_size], buf, size);
ff_rtp_send_data(s1, s->buf, size + header_size, last);
}
}
注意一点：到目前为至没有找个定义H265的payload值，从ffmpeg的源码分析只有一个96，说明H265的payload值需要自定义，用96或其它值。
更新：此方式经VLC2.2.1测试通过。