FFmpeg⾥⾯有ts打包和解包的代码，这⾥简单介绍下怎么使⽤吧。
先来看下FFmpeg⽬录结构：
libavformat：⽤于各种⾳视频的⽣成和解析，包括获取解码所需信息以⽣成解码上下⽂结构和读取⾳视频帧等功能； libavcodec：⽤于各种类型声⾳/编解码；
libavutil：包含⼀些公共的⼯具函数；
libswscale：⽤于视频场景⽐例缩放、⾊彩映射转换；
libpostproc：⽤于后期效果处理；
ffmpeg：该项⽬提供的⼀个⼯具，可⽤于格式转换、解码或即时编码等；
ffsever：⼀个HTTP 多媒体即时⼴播串流服务器；
ffplay：是⼀个简单的播放器，使⽤ffmpeg库解析和解码，通过SDL显⽰；
libavformat⽬录下 mpegtsenc.c，mpegts.c 分别是ts打包和解包的代码：
下⾯介绍下mpegtsenc.c⼀些重要函数（原理请看 iso 13818-1）：
mpegts_write_pat(AVFormatContext *s)；
mpegts_write_pmt(AVFormatContext *s, MpegTSService *service)
mpegts_write_sdt(AVFormatContext *s)//节⽬描述表
pat，pmt这两个表是ts打包最重要的表，这两个表说⽩了就是多路复⽤的⼀个索引，解码器需要更具PAT知道有哪些节⽬(可以理解为电视节⽬)，根据PMT 知道每个节⽬⾥⾯有哪些es流（每个电视节⽬都有⾳频和视频），这两个函数⼀般是不需要改动的；
pat，pmt的信息并不是只是开始打包的时候出现，看mpegts_write_pes代码会发现着两个表是根据retransmit_si_info计算出来的。
看下mpegts_write_pmt部分代码：
01. //nb_streams 对应es流，如果⼀路⾳频⼀路视频，nb_streams=2
02. for(i = 0; i < s->nb_streams; i++) {
03. AVStream *st = s->streams[i];
04. MpegTSWriteStream *ts_st = st->priv_data;
05. switch(st->codec->codec_id) {
06. case CODEC_ID_MPEG1VIDEO:
07. case CODEC_ID_MPEG2VIDEO:
08. stream_type = STREAM_TYPE_VIDEO_MPEG2;
09. break;
10. case CODEC_ID_MPEG4:
11. stream_type = STREAM_TYPE_VIDEO_MPEG4;
12. break;
13. case CODEC_ID_H264:
14. stream_type = STREAM_TYPE_VIDEO_H264;
15. break;
16. case CODEC_ID_MP2:
17. case CODEC_ID_MP3:
18. stream_type = STREAM_TYPE_AUDIO_MPEG1;
19. break;
20. case CODEC_ID_AAC:
21. stream_type = STREAM_TYPE_AUDIO_AAC;
22. break;
23. case CODEC_ID_AC3:
24. stream_type = STREAM_TYPE_AUDIO_AC3;
25. break;
26. default:
27. stream_type = STREAM_TYPE_PRIVATE_DATA;
28. break;
29. }
30. *q++ = stream_type;
31. put16(&q, 0xe000 | ts_st->pid);
复制代码
从上⾯看出ts打包⽀持MPEG1，MPEG2，MPEG4，h264视频以及PCM，mp2,mp3,AAC,AC3⾳频，⾳频⽅⾯标准不⽀持G711等G开头的⾳频，当然如果⾃⼰开发客户端的话是可以⾃定义的。
2）mpegts_write_header(AVFormatContext *s)
初始化AVFormatContext参数，在正式封装开始加⼊PAT，PMT，SDT⼀些信息。代码中有基本的注释；
3）mpegts_write_pes(AVFormatContext *s, AVStream *st, const uint8_t *payload, int payload_size, int64_t pts, int64_t dts)
这个函数就是TS打包的主函数了，这个函数主要功能就是把⼀帧数据拆分成188字节（感觉效率低了点），并加⼊PTS，DTS同步信息，这个函数封装的对象是⼀帧视频或者⾳频数据，payload，payload_size分别是数据和⼤⼩。
PTS，DTS就是⾳视频同步时间戳，时间戳其实就是⼀次采样的颗粒(简单理解就是数据)，以视频来举例，视频同步时钟90K hz（27M/300），如果帧率是
25fps的话，⼀帧数据采样时间40ms，那么时间戳就是90K x 40ms = 3600（估算值）。
static void mpegts_write_pes(AVFormatContext *s, AVStream *st,
const uint8_t *payload, int payload_size,
int64_t pts, int64_t dts, int key)
{
........
while (payload_size >0) {
retransmit_si_info(s, force_pat); //评估是否需要插⼊PAT、PMT
force_pat =0;
write_pcr =0;
if (ts_st->pid == ts_st->service->pcr_pid) { //评估pes中是否需要插⼊PCR
if (ts->mux_rate >1 || is_start) // VBR pcr period is based on frames
ts_st->service->pcr_packet_count++;
if (ts_st->service->pcr_packet_count >=
ts_st->service->pcr_packet_period) {
ts_st->service->pcr_packet_count =0;
write_pcr =1;
}
}
if (ts->mux_rate >1&& dts != AV_NOPTS_VALUE &&
(dts - get_pcr(ts, s->pb)/300) > delay) { //CBR考虑(插⼊pcr_only或null_packet)
/* pcr insert gets priority over null packet insert */
if (write_pcr)
mpegts_insert_pcr_only(s, st);
else
mpegts_insert_null_packet(s);
continue; /* recalculate write_pcr and possibly retransmit si_info */
}
/* prepare packet header */
q = buf;
*q++= 0x47;
val = (ts_st->pid >>8);
if (is_start)
val |= 0x40; //payload_unit_start_indicator
*q++= val;
*q++= ts_st->pid;
ts_st->cc = (ts_st->cc +1) & 0xf; //continuity_counter
*q++= 0x10 | ts_st->cc; // payload indicator + CC
/*********写⼊adaptation_field(如果需要) *********/
if (key && is_start && pts != AV_NOPTS_VALUE) {
if (ts_st->pid == ts_st->service->pcr_pid)
write_pcr =1;
set_af_flag(buf, 0x40); //set Random Access for key frames
q = get_ts_payload_start(buf);暖通系统
}
if (write_pcr) {
set_af_flag(buf, 0x10); //PCR_flag
q = get_ts_payload_start(buf);
// add 11, pcr references the last byte of program clock reference base
if (ts->mux_rate >1)
pcr = get_pcr(ts, s->pb);
else
pcr = (dts - delay)*300;
if (dts != AV_NOPTS_VALUE && dts < pcr /300)
av_log(s, AV_LOG_WARNING, "dts < pcr, TS is invalid\n");
extend_af(buf, write_pcr_bits(q, pcr)); //写⼊pcr
q = get_ts_payload_start(buf);
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}
/
*********写⼊payload*********/
if (is_start) {
int pes_extension =0;
int pes_header_stuffing_bytes =0;
/* write PES header */
*q++= 0x00;
*q++= 0x00;
*q++= 0x01;
is_dvb_subtitle =0;
is_dvb_teletext =0;
/*写⼊stream_id */
if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
if (st->codec->codec_id == AV_CODEC_ID_DIRAC) {
*q++= 0xfd;
} else
*q++= 0xe0; //video stream
} else if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO &&
(st->codec->codec_id == AV_CODEC_ID_MP2 ||
st->codec->codec_id == AV_CODEC_ID_MP3 ||
st->codec->codec_id == AV_CODEC_ID_AAC)) {
*q++= 0xc0;
} else if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO &&格宾加筋挡墙
st->codec->codec_id == AV_CODEC_ID_AC3 &&
ts->m2ts_mode) {
*q++= 0xfd;
} else {
*q++= 0xbd;
if(st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
if (st->codec->codec_id == AV_CODEC_ID_DVB_SUBTITLE) {
is_dvb_subtitle =1;
} else if (st->codec->codec_id == AV_CODEC_ID_DVB_TELETEXT) {
is_dvb_teletext =1;
}
}
}
header_len =0;
flags =0;
/*处理PTS_DTS_flags */
if (pts != AV_NOPTS_VALUE) {
header_len +=5;
flags |= 0x80;
}
if (dts != AV_NOPTS_VALUE && pts != AV_NOPTS_VALUE && dts != pts) {
header_len +=5;
flags |= 0x40;
}
........
len= payload_size + header_len +3;
/*3 extra bytes should be added to DVB subtitle payload: 0x20 0x00 at the beginning and trailing 0xff */
if (is_dvb_subtitle) {
len+=3;
payload_size++;
}
if (len> 0xffff)
len=0;
if (ts->omit_video_pes_length && st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
len=0;
}
霍云成*q++=len>>8; //PES_packet_length
*q++=len;
val = 0x80; //'10'
/* data alignment indicator is required for subtitle and data streams */
if (st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE || st->codec->codec_type == AVMEDIA_TYPE_DATA) val |= 0x04;
net-link
*q++= val;
*q++= flags;
*q++= header_len; //PES_header_data_length
if (pts != AV_NOPTS_VALUE) {
write_pts(q, flags >>6, pts); //写⼊pts
q +=5;
}
if (dts != AV_NOPTS_VALUE && pts != AV_NOPTS_VALUE && dts != pts) {
write_pts(q, 1, dts); //写⼊dts
q +=5;
}
........
/*处理完header，下⾯开始处理数据*/
/* header size */
header_len = q - buf;
/* data len*/
len= TS_PACKET_SIZE - header_len;
if (len> payload_size) //pes包太⼤，⼀个ts包发不完，就得拆包。
len= payload_size;
stuffing_len = TS_PACKET_SIZE - header_len -len; //相反，如果太⼩，就加⼊填充。
if (stuffing_len >0) {
/* add stuffing with AFC *///
if (buf[3] & 0x20) {
/* stuffing already present: increase its size */
afc_len = buf[4] +1;
memmove(buf +4+ afc_len + stuffing_len,
buf +4+ afc_len,
赫塔米勒
header_len - (4+ afc_len));
buf[4] += stuffing_len;
memset(buf +4+ afc_len, 0xff, stuffing_len);
} else {
/* add stuffing */
memmove(buf +4+ stuffing_len, buf +4, header_len -4);
buf[3] |= 0x20;
buf[4] = stuffing_len -1;
if (stuffing_len >=2) {
buf[5] = 0x00;
memset(buf +6, 0xff, stuffing_len -2);
}
}
}
if (is_dvb_subtitle && payload_size ==len) {
memcpy(buf + TS_PACKET_SIZE -len, payload, len-1);
buf[TS_PACKET_SIZE -1] = 0xff; /* end_of_PES_data_field_marker: an 8-bit field with fixed contents 0xff for DVB subtitle */
} else {
memcpy(buf + TS_PACKET_SIZE -len, payload, len); //写⼊payload数据
}
payload +=len;
payload_size -=len;
mpegts_prefix_m2ts_header(s);
avio_write(s->pb, buf, TS_PACKET_SIZE); //写⼊avio(缓存到avio_buf中)
}
avio_flush(s->pb); //把avio_buf的数据写⼊后端(file/udp等)
ts_st->prev_payload_key = key;
}
4）mpegts_write_packet(AVFormatContext *s, AVPacket *pkt)
这个函数功能⽐较简单，就是把⼀帧数据拆分成⼏个块来封装成pes，因为pes头信息的长度只有两个字节长度（当时可能⾯向标清），⾼清的I帧数据肯定⼀次包不完的。
static int mpegts_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
{
........
if (st->codec->codec_id == AV_CODEC_ID_H264) {
const uint8_t *p = buf, *buf_end = p+size;
uint32_t state =-1;
int ret = ff_check_h264_startcode(s, st, pkt);
if (ret <0)
return ret;
do {
p = avpriv_find_start_code(p, buf_end, &state);
av_dlog(s, "nal %d\n", state & 0x1f);
} while (p < buf_end && (state & 0x1f) !=9&&
(state & 0x1f) !=5&& (state & 0x1f) !=1); //nal_unit_type
if ((state & 0x1f) !=9) { // AUD NAL
data = av_malloc(pkt->size+6);
if (!data)
return AVERROR(ENOMEM);
memcpy(data+6, pkt->data, pkt->size);
AV_WB32(data, 0x00000001);
data[4] = 0x09;
data[5] = 0xf0; // any slice type (primary_pic_type = 0xe) + rbsp stop one bit
buf = data;
size = pkt->size+6;
}
if (pkt->dts != AV_NOPTS_VALUE) {
int i;
for(i=0; i<s->nb_streams; i++){
AVStream *st2 = s->streams[i];
MpegTSWriteStream *ts_st2 = st2->priv_data;
if( ts_st2->payload_size
&& (ts_st2->payload_dts == AV_NOPTS_VALUE || dts - ts_st2->payload_dts > delay/2)){
mpegts_write_pes(s, st2, ts_st2->payload, ts_st2->payload_size,
ts_st2->payload_pts, ts_st2->payload_dts,
ts_st2->payload_flags & AV_PKT_FLAG_KEY); //优先处理其它码流fifo数据(多码流同步考虑) ts_st2->payload_size =0;
}
}
}
if (ts_st->payload_size && ts_st->payload_size + size > ts->pes_payload_size) {
mpegts_write_pes(s, st, ts_st->payload, ts_st->payload_size,
ts_st->payload_pts, ts_st->payload_dts,
ts_st->payload_flags & AV_PKT_FLAG_KEY); //处理当前码流fifo数据
ts_st->payload_size =0;
}
if (st->codec->codec_type != AVMEDIA_TYPE_AUDIO || size > ts->pes_payload_size) {
av_assert0(!ts_st->payload_size);
//for video and subtitle, write a single pes packet
mpegts_write_pes(s, st, buf, size, pts, dts, pkt->flags & AV_PKT_FLAG_KEY); //满⼀个pes帧，直接写⼊。 av_free(data);
return 0;
}
if (!ts_st->payload_size) { //初始化pts、dts
ts_st->payload_pts = pts;
ts_st->payload_dts = dts;
ts_st->payload_flags = pkt->flags;
}
memcpy(ts_st->payload + ts_st->payload_size, buf, size); //不满⼀个pes帧，先缓存到fifo。
ts_st->payload_size += size;
av_free(data);
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