SRS之SrsHls::on_video详解
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1. SrsHls::on_video
/*
* mux the video packets to ts.
* @param shared_video, directly ptr, copy it if need to save it.
* @param is_sps_pps, whether the video is h.264 sps/pps.
*/
int SrsHls::on_video(SrsSharedPtrMessage* shared_video, bool is_sps_pps)
{
int ret = ERROR_SUCCESS;
if (!hls_enabled) {
return ret;
}
/* update the hls time, for hos_dispose. */
last_update_time = srs_get_system_time_ms();
SrsSharedPtrMessage* video = shared_video->copy();
SrsAutoFree(SrsSharedPtrMessage, video);
/* user can disable the sps parse to workaround when parse sps failed. */
if (is_sps_pps) {
/* 是否使能解析 sps，默认使能 */
codec->avc_parse_sps = _srs_config->get_parse_sps(_req->vhost);
}
sample->clear();
/* demux the video packet in h.264 codec.
* the packet mux in FLV/RTMP format defined in flv specification.
* demux the video specified data(frame_type, codec_id, ...) to sample.
* demux the h.264 specified data(avc_profile, ...) to codec from sequence header.
* demux the h.264 NALUs to sample units. */
if ((ret = codec->video_avc_demux(video->payload, video->size, sample))
!= ERROR_SUCCESS) {
srs_error("hls codec demux video failed. ret=%d", ret);
return ret;
}
/* ignore info frame */
if (sample->frame_type == SrsCodecVideoAVCFrameVideoInfoFrame) {
return ret;
}
if (codec->video_codec_id != SrsCodecVideoAVC) {
return ret;
}
/* ignore sequence header */
if (sample->frame_type == SrsCodecVideoAVCFrameKeyFrame
&& sample->avc_packet_type == SrsCodecVideoAVCTypeSequenceHeader) {
return hls_cache->on_sequence_header(muxer);
}
/* TODO: FIXME: config the jitter of HLS. */
if ((ret = jitter->correct(video, SrsRtmpJitterAlgorithmOFF)) != ERROR_SUCCESS) {
srs_error("rtmp jitter correct video failed. ret=%d", ret);
return ret;
}
/* flv 的时间戳（单位 ms）将每一秒分为 90000 份，因此为 1/90 ms */
int64_t dts = video->timestamp * 90;
stream_dts = dts;
/* write video to muxer */
if ((ret = hls_cache->write_video(codec, muxer, dts, sample)) != ERROR_SUCCESS) {
srs_error("hls cache write video failed. ret=%d", ret);
return ret;
}
/* pithy print message. */
hls_show_mux_log();
return ret;
}2. SrsAvcAacCodec::video_avc_demux
接收到一个视频消息，首先调用该函数解析该视频数据。
int SrsAvcAacCodec::video_avc_demux(char* data, int size, SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
sample->is_video = true;
if (!data || size <= 0) {
srs_trace("no video present, ignore it.");
return ret;
}
if ((ret = stream->initialize(data, size)) != ERROR_SUCCESS) {
return ret;
}
/* video decode */
if (!stream->require(1)) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("avc decode frame_type failed. ret=%d", ret);
return ret;
}
/* Video Tag 数据区的第一个字节是视频信息 */
/* E.4.3 Video Tags, video_file_format_spec_v10_1.pdf, page 78 */
int8_t frame_type = stream->read_1bytes();
/* 编码ID：4bits */
int8_t codec_id = frame_type & 0x0f;
/* 帧类型：4bits */
frame_type = (frame_type >> 4) & 0x0f;
sample->frame_type = (SrsCodecVideoAVCFrame)frame_type;
/* ignore info frame without error
* @see https://github.com/ossrs/srs/issues/288#issuecomment-69863909 */
if (sample->frame_type == SrsCodecVideoAVCFrameVideoInfoFrame) {
srs_warn("avc igone the info frame, ret=%d", ret);
return ret;
}
/* only support h.264/avc */
if (codec_id != SrsCodecVideoAVC) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("avc only support video h.264/avc codec. actual=%d, ret=%d",
codec_id, ret);
return ret;
}
video_codec_id = codec_id;
if (!stream->require(4)) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("avc decode avc_packet_type failed. ret=%d", ret);
return ret;
}
/* AVC Packet 类型：1byte, 0: AVC序列头, 1: AVC NALU 单元 */
int8_t avc_packet_type = stream->read_1bytes();
/* CTS: 3bytes，如果 AVC packet 类型为 1，则为 cts 偏移，其他情况则为 0
* cts = (pts - dts) / 90，单位毫秒 */
int32_t composition_time = stream->read_3bytes();
/* pts = dts + cts. */
sample->cts = composition_time;
sample->avc_packet_type = (SrsCodecVideoAVCType)avc_packet_type;
if (avc_packet_type == SrsCodecVideoAVCTypeSequenceHeader) {
/* 解析 sps，pps 数据 */
if ((ret = avc_demux_sps_pps(stream)) != ERROR_SUCCESS) {
return ret;
}
} else if (avc_packet_type == SrsCodecVideoAVCTypeNALU){
/* 检测 H264 的封装格式为 AnnexB 还是 "ISO Base Media File Format"，
* 然后根据相应封装格式的特点提取出 NALU，将该 NALU 保存到 sample 的
* sample_units 数组中 */
if ((ret = video_nalu_demux(stream, sample)) != ERROR_SUCCESS) {
return ret;
}
} else {
/* ignored. */
}
return ret;
}接下来，若检测接收到的 video packet type 为 1，即为 NAL 单元，则调用 video_nalu_demux 进行解封装。
2.1 SrsAvcAacCodec::video_nalu_demux
int SrsAvcAacCodec::video_nalu_demux(SrsStream* stream, SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
/* ensure the sequence header demuxed */
if (!is_avc_codec_ok()) {
srs_warn("avc ignore type=%d for no sequence header. ret=%d",
SrsCodecVideoAVCTypeNALU, ret);
return ret;
}
/* 在 SrsAvcAacCodec 构造函数中初始化该变量为 SrsAvcPayloadFormatGuess */
/* guess for the first time. */
if (payload_format == SrsAvcPayloadFormatGuess) {
/* One or more NALUs (Full frames are required)
* try "AnnexB" from H.264-AVC-ISO_IEC_14496-10.pdf, page 211. */
if ((ret = avc_demux_annexb_format(stream, sample)) != ERROR_SUCCESS) {
/* stop try when system error. */
if (ret != ERROR_HLS_AVC_TRY_OTHERS) {
srs_error("avc demux for annexb failed. ret=%d", ret);
return ret;
}
/* try "ISO Base Media File Format" from
* H.264-AVC-ISO_IEC_14496-15.pdf, page 20" */
if ((ret = avc_demux_ibmf_format(stream, sample)) != ERROR_SUCCESS) {
return ret;
} else {
payload_format = SrsAvcPayloadFormatIbmf;
srs_info("hls guess avc payload is ibmf format.");
}
} else {
payload_format = SrsAvcPayloadFormatAnnexb;
srs_info("hls guess avc payload is annexb format.");
}
} else if (payload_format == SrsAvcPayloadFormatIbmf) {
/* try "ISO Base Media File Format" from H.264-AVC-ISO_IEC_14496-15.pdf, page 20 */
if ((ret = avc_demux_ibmf_format(stream, sample)) != ERROR_SUCCESS) {
return ret;
}
srs_info("hls decode avc payload in ibmf format.");
} else {
/* One or more NALUs (Full frames are required)
* try "AnnexB" from H.264-AVC-ISO_IEC_14496-10.pdf, page 211. */
if ((ret = avc_demux_annexb_format(stream, sample)) != ERROR_SUCCESS) {
/* ok, we guess out the payload is annexb, but maybe changed to ibmf. */
if (ret != ERROR_HLS_AVC_TRY_OTHERS) {
srs_error("avc demux for annexb failed. ret=%d", ret);
return ret;
}
/* try "ISO Base Media File Format" from
* H.264-AVC-ISO_IEC_14496-15.pdf, page 20 */
if ((ret = avc_demux_ibmf_format(stream, sample)) != ERROR_SUCCESS) {
return ret;
} else {
payload_format = SrsAvcPayloadFormatIbmf;
srs_warn("hls avc payload change from annexb to ibmf format.");
}
}
srs_info("hls decode avc payload in annexb format.");
}
return ret;
}下面先尝试为当前的 H264 封装为 Annexb 格式，因此调用 SrsAvcAacCodec::avc_demux_annexb_format 函数进行解析。
2.2 SrsAvcAacCodec::avc_demux_annexb_format
int SrsAvcAacCodec::avc_demux_annexb_format(SrsStream* stream, SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
/* not annexb, try others */
if (!srs_avc_startswith_annexb(stream, NULL)) {
return ERROR_HLS_AVC_TRY_OTHERS;
}
/* AnnexB
* B.1.1 Byte stream NAL unit syntax,
* H.264-AVC-ISO_IEC_14496-10.pdf, page 211.
*/
while (!stream->empty()) {
/* find start code */
int nb_start_code = 0;
if (!srs_avc_startswith_annexb(stream, &nb_start_code)) {
return ret;
}
/* skip the start code. */
if (nb_start_code > 0) {
stream->skip(nb_start_code);
}
/* the NALU start bytes. */
char* p = stream->data() + stream->pos();
/* get the last matched NALU */
while (!stream->empty()) {
if (srs_avc_startswith_annexb(stream, NULL)) {
break;
}
stream->skip(1);
}
/* 此时 pp 指向下一个 NALU start bytes */
char* pp = stream->data() + stream->pos();
/* skip the empty. */
if (pp - p <= 0) {
continue;
}
/* 获取到一个 NALU 后，将该 NALU 添加到 sample 中的 sample_units 数组中 */
/* got the NALU. */
if ((ret = sample->add_sample_unit(p, pp - p)) != ERROR_SUCCESS) {
srs_error("annexb add video sample failed. ret=%d", ret);
return ret;
}
}
return ret;
}2.2.1 srs_avc_startswith_annexb
/*
* whether stream starts with the avc NALU in "AnnexB"
* from H.264-AVC-ISO_IEC_14496-10.pdf, page 211.
* start code must be "N[00] 00 00 01" where N>=0
* @param pnb_start_code, output the size of start code, must >=3.
* NULL to ignore.
*/
bool srs_avc_startswith_annexb(SrsStream* stream, int* pnb_start_code)
{
char* bytes = stream->data() + stream->pos();
char* p = bytes;
for ( ;; ) {
if (!stream->require(p - bytes + 3)) {
return false;
}
/* not match */
if (p[0] != (char)0x00 || p[1] != (char)0x00) {
return false;
}
/* match N[00] 00 00 01, where N>=0 */
if (p[2] == (char)0x01) {
if (pnb_start_code) {
*pnb_start_code = (int)(p - bytes) + 3;
}
return true;
}
p++;
}
return false;
}由该代码可知，若 H264 为 Annexb 封装格式，则 NALU 之间是以 0x000001（3bytes） 或者 0x00000001（4bytes） 分割。
2.2.2 SrsCodecSample::add_sample_unit
/*
* add the a sample unit, it‘s a h.264 NALU or aac raw data.
* the sample unit directly use the ptr of packet bytes,
* so user must never use sample unit when packet is destroyed.
* in a word, user must clear sample before demux it.
*/
int SrsCodecSample::add_sample_unit(char* bytes, int size)
{
int ret = ERROR_SUCCESS;
/* sample_units 数组的最大值为 128 */
if (nb_sample_units >= SRS_SRS_MAX_CODEC_SAMPLE) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("hls decode samples error, "
"exceed the max count: %d, ret=%d", SRS_SRS_MAX_CODEC_SAMPLE, ret);
return ret;
}
/* 从 sample_uints 数组中取出一个 sample_unit，用于存放获取到的 NALU 或 aac raw data */
SrsCodecSampleUnit* sample_unit = &sample_units[nb_sample_units++];
sample_unit->bytes = bytes;
/* 该 NALU 单元的大小 或 aac raw data 的大小 */
sample_unit->size = size;
// for video, parse the nalu type, set the IDR flag.
if (is_video) {
SrsAvcNaluType nal_unit_type = (SrsAvcNaluType)(bytes[0] & 0x1f);
if (nal_unit_type == SrsAvcNaluTypeIDR) {
/* 若当前 NALU 为 I 帧，则置位该标志位，表示当前 sample_units 数组中含有 I 帧 */
has_idr = true;
} else if (nal_unit_type == SrsAvcNaluTypeSPS ||
nal_unit_type == SrsAvcNaluTypePPS) {
/* Whether exists SPS/PPS NALU. */
has_sps_pps = true;
} else if (nal_unit_type == SrsAvcNaluTypeAccessUnitDelimiter) {
/* Whether exists AUD NALU. */
has_aud = true;
}
if (first_nalu_type == SrsAvcNaluTypeReserved) {
/* 记录 sample_units 数组中第一个 NALU 的类型 */
first_nalu_type = nal_unit_type;
}
}
return ret;
}- 若上面尝试调用
avc_demux_annexb_format函数失败返回，即表明当前 H.264 不是以 AnnexB 格式封装的（即各 NALU 单元之间不是以 0x000001 或 0x00000001 分割的），则接下来尝试调用avc_demux_ibmf_format函数进行解封装，即再次尝试该 H.264 是否为ISO Base Media File Format。
2.3 SrsAvcAacCodec::avc_demux_ibmf_format
/*
* demux the avc NALU in "ISO Base Media File Format"
* from H.264-AVC-ISO_IEC_14496-15.pdf, page 20
*/
int SrsAvcAacCodec::avc_demux_ibmf_format(SrsStream* stream, SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
int PictureLength = stream->size() - stream->pos();
/*
* 5.3.4.2.1 Syntax, H.264-AVC-ISO_IEC_14496-15.pdf, page 16
* 5.2.4.1 AVC decoder configuration record
* 5.2.4.1.2 Semantics
* The value of this field shall be one of 0, 1, or 3 corresponding to a
* length encoded with 1, 2, or 4 bytes, respectively.
*/
srs_assert(NAL_unit_length != 2);
/*
* 该 NAL_unit_length 的值即为解析 sps 的获取到的 lengthSizeMinusOne 字段值
*/
/* 5.3.4.2.1 Syntax, H.264-AVC-ISO_IEC_14496-15.pdf, page 20 */
for (int i = 0; i < PictureLength; ) {
/* unsigned int((NAL_unit_length+1)*8) NALUnitLength; */
if (!stream->require(NAL_unit_length + 1)) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("avc decode NALU size failed. ret=%d", ret);
return ret;
}
int32_t NALUnitLength = 0;
if (NAL_unit_length == 3) {
NALUnitLength = stream->read_4bytes();
} else if (NAL_unit_length == 1) {
NALUnitLength = stream->read_2bytes();
} else {
NALUnitLength = stream->read_1bytes();
}
/* maybe stream is invalid format.
* see: https://github.com/ossrs/srs/issues/183 */
if (NALUnitLength < 0) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("maybe stream is AnnexB format. ret=%d", ret);
return ret;
}
/* NALUnit */
if (!stream->require(NALUnitLength)) {
ret = ERROR_HLS_DECODE_ERROR;
srs_error("avc decode NALU data failed. ret=%d", ret);
return ret;
}
/* 7.3.1 NAL unit syntax, H.264-AVC-ISO_IEC_14496-10.pdf, page 44. */
if ((ret = sample->add_sample_unit(stream->data() + stream->pos(), NALUnitLength))
!= ERROR_SUCCESS) {
srs_error("avc add video sample failed. ret=%d", ret);
return ret;
}
stream->skip(NALUnitLength);
i += NAL_unit_length + 1 + NALUnitLength;
}
return ret;
}- 由该函数源码可知，若 H264 为
ISO Base Media File Format，则各个 NALUnit 之间是以 1byte 或 2bytes 或 4bytes 分割的，这 1byte 或 2bytes 或 4bytes 即为NALUnitLength所占的字节数，具体为 1byte 还是 2bytes 或者 4bytes 是由 sps 中的lengthSizeMinusOne值决定的。若lengthSizeMinusOne值为 3，则NALUnitLength占 4bytes；若lengthSizeMinusOne值为 1，则NALUnitLength占 2bytes；若lengthSizeMinusOne值为 0，则ALUnitLength占 1 字节。
3. SrsHlsCache::write_video
/*
* write video to muxer.
*/
int SrsHlsCache::write_video(SrsAvcAacCodec* codec, SrsHlsMuxer* muxer,
int64_t dts, SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
/* write video to cache. */
if ((ret = cache->cache_video(codec, dts, sample)) != ERROR_SUCCESS) {
return ret;
}
/* when segment overflow, reap if possible */
if (muxer->is_segment_overflow()) {
/* do reap ts if any of:
* a. wait keyframe and got keyframe.
* b. always reap when not wait keyframe */
if (!muxer->wait_keyframe() ||
sample->frame_type == SrsCodecVideoAVCFrameKeyFrame) {
/* reap the segmtn, which will also flush the video. */
if ((ret = reap->segment("video", muxer, cache->video->dts))
!= ERROR_SUCCESS) {
return ret;
}
}
}
/* flush video when got one */
if ((ret = muxer->flush_video(cache)) != ERROR_SUCCESS) {
srs_error("m3u8 muxer flush video failed. ret=%d", ret);
return ret;
}
return ret;
}- 在
SrsHlsCache::write_video函数中，首先调用SrsTsCache::cache_video函数将已经保存在 sample 中成员 sample_units 数组中的 NALU 保存到 cache 中。
3.1 SrsTsCache::cache_video
int SrsTsCache::cache_video(SrsAvcAacCodec* codec, int64_t dts,
SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
/* create the ts video message. */
if (!video) {
video = new SrsTsMessage();
/*
* write_pcr:
* whether thisi message with pcr info,
* generally, the video IDR(I frame, the keyframe of h.264) carray the pcr info.
*/
/* 若当前帧类型为 I帧，表明携带有 pcr 信息 */
video->write_pcr = sample->frame_type == SrsCodecVideoAVCFrameKeyFrame;
/*
* start_pts:
* the audio cache buffer start pts, to flush audio if full.
* @remark, the pts is not the adjust one, it‘s the original pts.
*/
video->start_pts = dts;
}
/* 对于 video，flv/rtmp 的时间戳即为 video 的 dts */
video->dts = dts;
/* pts = dts + cts */
video->pts = video->dts + sample->cts * 90; // in ms
/* stream id, 视频取值为 (0xe0~0xef)，通常为 0xe0，这里即 SrsTsPESStreamIdVideoCommon */
video->sid = SrsTsPESStreamIdVideoCommon;
/* write video to cache. */
if ((ret = do_cache_avc(codec, sample)) != ERROR_SUCCESS) {
return ret;
}
return ret;
}若当前 SrsTsCache 之前从未缓存过视频数据，即 video 为 NULL，则构建一个新的 SrsTsMessage 类的对象，video 指向该对象。
3.1.1 SrsTsMessage 构造
/*
* the media audio/video message parsed from PES packet.
*/
SrsTsMessage::SrsTsMessage(SrsTsChannel* c, SrsTsPacket* p)
{
/*
* channel and packet:
* decoder only,
* the ts message does not use them,
* for user to get the channel and packet.
*/
channel = c;
packet = p;
/*
* dts and pts:
* the timestamp in 90khz
*/
dts = pts = 0;
/*
* sid:
* the id of pes stream to indicates the payload codec.
* @remark use is_audio() and is_video() to check it,
* and stream_number() to finger it out.
*/
sid = (SrsTsPESStreamId)0x00;
/*
* continuity_counter: the chunk id.
*/
continuity_counter = 0;
/*
* PES_packet_length: the size of payload, 0 indicates the length() of payload.
*/
PES_packet_length = 0;
/*
* payload: the payload bytes.
*/
payload = new SrsSimpleBuffer();
/*
* is_discontinuity: whether got discontinuity ts, for example,
* sequence header changed.
*/
is_discontinuity = false;
/*
* start_pts: the audio cache buffer start pts, to flush audio if full.
* @remark the pts is not the adjust one, it‘s the orignal pts.
*/
start_pts = 0;
/*
* write_pcr:
* whether this message with pcr info,
* generally, the video IDR(I frame, the keyframe of h.264) carray the pcr info.
*/
write_pcr = false;
}- 在
SrsTsCache::cache_video函数中，构建 SrsTsMessage 并初始化时间戳等信息后，接着调用SrsTsCache::do_cache_avc函数将 video 数据写入到SrsTsCache.video->payload中.
3.1.2 SrsTsCache::do_cache_avc
int SrsTsCache::do_cache_avc(SrsAvcAacCodec* codec, SrsCodecSample* sample)
{
int ret = ERROR_SUCCESS;
/* whether aud inserted. */
bool aud_inserted = false;
/* Insert a default AUD NALU when no AUD in samples. */
if (!sample->has_aud) {
/*
* the aud(access unit delimiter) before each frame.
* 7.3.2.4 Access unit delimiter RBSP syntax
* H.264-AVC-ISO_IEC_14496-10-2012.pdf, page 66.
*
* primary_pis_type u(3), the first 3bits, primary_pic_type indicates
* that the slice_type values for all slices of the primary coded
* picture are numbers of the set listed in Table 7-5 for the given
* value of primary_pic_type.
* 0, slice_type 2, 7
* 1, slice_type 0, 2, 5, 7
* 2, slice_type 0, 1, 2, 5, 6, 7
* 3, slice_type 4, 9
* 4, slice_type 3, 4, 8, 9
* 5, slice_type 2, 4, 7, 9
* 6, slice_type 0, 2, 3, 4, 5, 7, 8, 9
* 7, slice_type 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
* 7.4.2.4 Access unit delimiter RBSP semantics
* H.264-AVC-ISO_IEC_14496-10-2012.pdf, page 102.
*
* slice_type specifies the coding type of the slice according to Table 7-6.
* 0, P (P slice)
* 1, B (B slice)
* 2, I (I slice)
* 3, SP (SP slice)
* 4, SI (SI slice)
* 5, P (P slice)
* 6, B (B slice)
* 7, I (I slice)
* 8, SP (SP slice)
* 9, SI (SI slice)
* H.264-AVC-ISO_IEC_14496-10-2012.pdf, page 105.
*/
static u_int8_t default_aud_nalu[] = { 0x09, 0xf0 };
/* 这里封装 H264 使用的是 Annexb 格式，在 aud 前会插入
* 4 字节的分隔符: 0x00000001 */
srs_avc_insert_aud(video->payload, aud_inserted);
video->payload->append((const char*)default_aud_nalu, 2);
}
/* 除了 AUD 前插入的是 4 字节的分隔符 0x00000001 外，其他的
* NALU 前插入的都为 3 字节的分隔符: 0x000001 */
bool is_sps_pps_appended = false;
/* all sample use cont nalu header, except the sps-pps before IDR frame. */
for (int i = 0; i < sample->nb_sample_units, i++) {
SrsCodecSampleUnit* sample_unit = &sample->sample_units[i];
int32_t size = sample_unit->size;
if (!sample_unit->bytes || size <= 0) {
ret = ERROR_HLS_AVC_SAMPLE_SIZE;
srs_error("invalid avc sample length=%d, ret=%d", size, ret);
return ret;
}
/*
* 5bits, 7.3.1 NAL unit syntax,
* H.264-AVC-ISO_IEC_14496-10-2012.pdf, page 83.
*/
SrsAvcNaluType nal_unit_type = (SrsAvcNaluType)(sample_unit->bytes[0] & 0x1f);
/* 在 IDR 帧前先插入 sps 和 pps */
/*
* Insert sps/pps before IDR when there is no sps/pps in samples.
* The sps/pps is parsed from sequence header(generally the first flv packet).
*/
if (nal_unit_type == SrsAvcNaluTypeIDR &&
!sample->has_sps_pps && !is_sps_pps_appended) {
if (codec->sequenceParameterSetLength > 0) {
/* 插入 3 字节的分隔符: 0x000001 */
srs_avc_insert_aud(video->payload, aud_inserted);
/* 接着插入 sps */
video->payload->append(codec->sequenceParameterSetNALUnit,
codec->sequenceParameterSetLength);
}
if (codec->pictureParameterSetLength > 0) {
srs_avc_insert_aud(video->payload, aud_inserted);
video->payload->append(codec->pictureParameterSetNALUnit,
codec->pictureParameterSetLength);
}
is_sps_pps_appended = true;
}
/* Insert the NALU to video in annexb. */
srs_avc_insert_aud(video->payload, aud_inserted);
video->payload->append(sample->unit->bytes, sample->unit->size);
}
return ret;
}若当前为接收到 sps 和 pps 后的第二个 video 消息，则根据上面源码可知，在 video->payload 中各 nalu 之间的格式为：
annexb 4B header, 2B aud(nal_unit_type:9)(0x09 0xf0)(AUD)
annexb 3B header, 19B sps(nal_unit_type:7)(SPS)
annexb 3B header, 4B pps(nal_unit_type:8)(PPS)
annexb 3B header, 12B nalu(nal_unit_type:6)(SEI)
annexb 3B header, 2762B nalu(nal_unit_type:5)(IDR)- 在
SrsTsCache::do_cache_avc函数中，首先检测 sample 中是否已经有 aud（即接入单元定界符），若没有，则首先在video->payload中插入一个 aud。
3.1.3 srs_avc_insert_aud
void srs_avc_insert_aud(SrsSimpleBuffer* payload, bool& aud_inserted)
{
/*
* mux the samples in annexb format,
* H.264-AVC-ISO_IEC_14496-10-2012.pdf, page 324. */
/**
* 00 00 00 01 // header
* xxxxxxx // data bytes
* 00 00 01 // continue header
* xxxxxx // data bytes
*
* nal_unit_type specifies the type of RBSP data structure contained in the NAL
* unit as specified in Table 7-1.
* Table 7-1 - NAL unit type codec, syntax element categories, and NAL unit
* type classes H.264-AVC-ISO_IEC_14496-10-2012.pdf, page 83.
* 1, Coded slice of a non-IDR picture slice_layer_without_partitioning_rbsp( )
* 2, Coded slice data partition A slice_data_partition_a_layer_rbsp( )
* 3, Coded slice data partition B slice_data_partition_b_layer_rbsp( )
* 4, Coded slice data partition C slice_data_partition_c_layer_rbsp( )
* 5, Coded slice of an IDR picture slice_layer_without_partitioning_rbsp( )
* 6, Supplemental enhancement information (SEI) sei_rbsp( )
* 7, Sequence parameter set seq_parameter_set_rbsp( )
* 8, Picture parameter set pic_parameter_set_rbsp( )
* 9, Access unit delimiter access_unit_delimiter_rbsp( )
* 10, End of sequence end_of_seq_rbsp( )
* 11, End of stream end_of_stream_rbsp( )
* 12, Filler data filler_data_rbsp( )
* 13, Sequence parameter set extension seq_parameter_set_extension_rbsp( )
* 14, Prefix NAL unit prefix_nal_unit_rbsp( )
* 15, Subset sequence parameter set subset_seq_parameter_set_rbsp( )
* 19, Coded slice of an auxiliary coded picture without partitioning
* slice_layer_without_partitioning_rbsp( )
* 20, Coded slice extension slice_layer_extension_rbsp( )
* the first ts message of apple sample:
* annexb 4B header, 2B aud(nal_unit_type:9)(0x09 0xf0)(AUD)
* annexb 3B header, 19B sps(nal_unit_type:7)(SPS)
* annexb 3B header, 4B pps(nal_unit_type:8)(PPS)
* annexb 3B header, 12B nalu(nal_unit_type:6)(SEI)
* annexb 3B header, 21B nalu(nal_unit_type:6)(SEI)
* annexb 3B header, 2762B nalu(nal_unit_type:5)(IDR)
* annexb 3B header, 3535B nalu(nal_unit_type:5)(IDR)
* the second ts message of apple ts sample:
* annexb 4B header, 2B aud(nal_unit_type:9)(0x09 0xf0)(AUD)
* annexb 3B header, 21B nalu(nal_unit_type:6)(SEI)
* annexb 3B header, 379B nalu(nal_unit_type:1)(non-IDR,P/B)
* annexb 3B header, 406B nalu(nal_unit_type:1)(non-IDR,P/B)
* @remark we use the sequence of apple
* samples http://ossrs.net/apple-sample/bipbopall.m3u8
*/
static u_int8_t fresh_nalu_header[] = { 0x00, 0x00, 0x00, 0x01 };
static u_int8_t cont_nalu_header[] = { 0x00, 0x00, 0x01 };
if (!aud_inserted) {
aud_inserted = true;
payload->append((const char*)fresh_nalu_header, 4);
} else {
payload->append((const char*)cont_nalu_header, 3);
}
}- 回到
SrsHlsCache::write_video函数中，调用SrsTsCache::cache_video将 sample 中的所有缓存的 nalu 都插入到SrsTsCache* cache->video->payload中后，接着调用SrsHlsMuxer::is_segment_overflow函数检测当前片的时长是否已经大于 hls_fragment 指定的时长（本配置为 10s），若已经满足，则表示已经可以切割该片了。否则调用SrsHlsMuxer::flush_video函数。
3.2 SrsHlsMuxer::is_segment_overflow
/*
* whether segment overflow.
* that is whether the current segment duration>=(the segment in config)
*/
bool SrsHlsMuxer::is_segment_overflow()
{
srs_assert(current);
/* 若当前片的时长小于最小片时长的2倍限制，即小于 2*100=200ms，则
* 表示当前片还不可以切割 */
/* to prevent very small segment. */
if (current->duration * 1000 < 2 * SRS_AUTO_HLS_SEGMENT_MIN_DURATION_MS) {
return false;
}
/* use N% deviation, to smoother. */
/* 默认没有使能 hls_ts_floor，即 deviation 为 0.0 */
double deviation = hls_ts_floor ?
SRS_HLS_FLOOR_REAP_PERCENT * deviation_ts * hls_fragment : 0.0;
return current->duration >= hls_fragment + deviation;
}该函数是检测当前片的时长是否已经大于配置文件中 hls_fragment 指定的片的最小时长，若是，则返回 true，表明可以切割该片了；否则，返回 false。
假设当前片的时长还没满足大于等于 hls_fragment，则
SrsHlsCache::write_video函数中接着调用SrsHlsMuxer::flush_video函数。
3.3 SrsHlsMuxer::flush_video
int SrsHlsMuxer::flush_video(SrsTsCache* cache)
{
int ret = ERROR_SUCCESS;
/* if current is NULL, segment is not open, ignore the flush event. */
if (!current) {
srs_warn("flush video ignored, for segment is not open.");
return ret;
}
/* 确保 cache 中有 video 数据，否则直接返回 */
if (!cache->video || cache->video->payload->length() <= 0) {
return ret;
}
srs_assert(current);
/* update the duration of segment. */
current->update_duration(cache->video->dts);
if ((ret = current->muxer->write_video(cache->video))
!= ERROR_SUCCESS) {
return ret;
}
/* write success, clear and free the msg */
srs_freep(cache->video);
return ret;
}- 该函数首先调用 SrsHlsSegment::update_duration 函数更新当前片的时长。
3.3.1 SrsHlsSegment::update_duration
/*
* update the segment duration.
* @param current_frame_dts, the dts of frame, in tbn of ts.
*/
void SrsHlsSegment::update_duration(int64_t current_segment_dts)
{
/*
* we use video/audio to update segment duration,
* so when reap segment, some previous audio frame will
* update the segment duration, which is nagetive,
* just ignore it.
*/
if (current_frame_dts < segment_start_dts) {
/* for atc and timestamp jump, reset the start dts. */
if (current_frame_dts < segment_start_dts -
SRS_AUTO_HLS_SEGMENT_TIMESTAMP_JUMP_MS * 90) {
srs_warn("hls timestamp jump %"PRId64"=>%"PRId64,
segment_start_dts, current_frame_dts);
segment_start_dts = current_frame_dts;
}
return;
}
duration = (current_frame_dts - segment_start_dts) / 90000.0;
srs_assert(duration >= 0);
return;
}- 更新完当前片的时长后，回到
SrsHlsMuxer::flush_video函数中，接着调用SrsTSMuxer::write_video函数将 video frame 写入到 ts 中。
3.3.2 SrsTSMuxer::write_video
/*
* write a video frame to ts
*/
int SrsTSMuxer::write_video(SrsTsMessage* video)
{
int ret = ERROR_SUCCESS;
/* 将 video frame 写入到 PES packet 中 */
if ((ret = context->encode(writer, video, vcodec, acodec))
!= ERROR_SUCCESS) {
srs_error("hls encode video failed. ret=%d", ret);
return ret;
}
return ret;
}3.3.3 SrsTsContext::encode
/*
* write the PES packet, the video/audio stream.
* @param msg, the video/audio msg to write to ts.
* @param vc, the video codec, write the PAT/PMT table when changed.
* @param ac, the audio codec, write the PAT/PMT table when changed.
*/
int SrsTsContext::encode(SrsFileWriter* writer, SrsTsMessage* msg,
SrsCodecVideo vc, SrsCodecAudio ac)
{
int ret = ERROR_SUCCESS;
SrsTsStream vs, as;
int16_t video_pid = 0, audio_pid = 0;
switch (vc) {
case SrsCodecVideoAVC:
vs = SrsTsStreamVideoH264;
video_pid = TS_VIDEO_AVC_PID;
break;
case SrsCodecVideoDisabled:
vs = SrsTsStreamReserved;
break;
case SrsCodecVideoReserved:
case SrsCodecVideoReserved1:
case SrsCodecVideoReserved2:
case SrsCodecVideoSorensonH263:
case SrsCodecVideoScreenVideo:
case SrsCodecVideoOn2VP6:
case SrsCodecVideoOn2VP6WithAlphaChannel:
case SrsCodecVideoScreenVideoVersion2:
vs = SrsTsStreamReserved;
break;
}
switch (ac) {
case SrsCodecAudioAAC:
as = SrsTsStreamAudioAAC;
audio_pid = TS_AUDIO_AAC_PID;
break;
case SrsCodecAudioMP3:
as = SrsTsStreamAudioMp3;
audio_pid = TS_AUDIO_MP3_PID;
break;
case SrsCodecAudioDisabled:
as = SrsTsStreamReserved;
break;
case SrsCodecAudioReserved1:
case SrsCodecAudioLinearPCMPlatformEndian:
case SrsCodecAudioADPCM:
case SrsCodecAudioLinearPCMLittleEndian:
case SrsCodecAudioNellymoser16kHzMono:
case SrsCodecAudioNellymoser8kHzMono:
case SrsCodecAudioNellymoser:
case SrsCodecAudioReservedG711AlawLogarithmicPCM:
case SrsCodecAudioReservedG711MuLawLogarithmicPCM:
case SrsCodecAudioReserved:
case SrsCodecAudiospeex:
case SrsCodecAudioReservedMP3_8kHz:
case SrsCodecAudioReservedDeviceSpecificSound:
as = SrsTsStreamReserved;
break;
}
if (as == SrsTsStreamReserved && vs == SrsTsStreamReserved) {
ret = ERROR_HLS_NO_STREAM;
srs_error("hls: no video or audio stream, vcodec=%d, acodec=%d. ret=%d",
vc, ac, ret);
return ret;
}
/* 当首次调用该函数将 audio/video frame 写入到 PES packet 中时，
* 需要将 vcodec 和 acodec 写入到 PAT/PMT table 中 */
/* when any codec changed, write PAT/PMT table. */
if (vcodec != vc || acodec != ac) {
vcodec = vc;
acodec = ac;
if ((ret = encode_pat_pmt(writer, video_pid, vs, audio_pid, as))
!= ERROR_SUCCESS) {
return ret;
}
}
if (msg->is_audio()) {
return encode_pes(writer, msg, audio_pid, as, vs == SrsTsStreamReserved);
} else {
return encode_pes(writer, msg, video_pid, vs, vs == SrsTsStreamReserved);
}
}- 在该函数中，若为第一次调用该函数将 video/audio 数据写入到 PES packet 中，则需要调用
SrsTsContext::encode_pat_pmt函数将 video 和 audio 的所用的编码格式 vcodec 和 acodec 以及流类型写入到 PAT/PMT 表中。
3.3.4 SrsTsContext::encode_pat_pmt
该函数的具体分析可见于： SRS之TS封装PAT和PMT
回到
SrsTsContext::encode函数中，首次将 PAT/PMT 写入到 ts 文件中后，接着检测到当前消息为视频，因此调用SrsTsContext::encode_pes函数把当前的视频消息封装成 ts 格式，然后写入到 ts 文件中。
3.3.5 SrsTsContext::encode_pes
该函数的具体分析： SRS之SrsTsContext::encode_pes详解
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