SRT: Fix bug for multiple NALUs, when configure OBS in zerolatency.

[runner365]

issue: #2390
the bug happen when obs push srt stream and configue h264 in zerolatency.

[xiaozhihong]

Is there a mistake here, head() - frame_size is a wild pointer?

TRANS_BY_GPT3

[xiaozhihong]

I probably understand.
Slice multiple frames and NALUs, previously sent one by one.
Now, after parsing the SPS/PPS, the rest is ignored and sent directly merged.

TRANS_BY_GPT3

[codecov-commenter]

Codecov Report

Merging #2440 (d7d9a85) into develop (ce47d5c) will not change coverage.
The diff coverage is n/a.

❗ Current head d7d9a85 differs from pull request most recent head 48c9fc7. Consider uploading reports for the commit 48c9fc7 to get more accurate results

@@           Coverage Diff            @@
##           develop    #2440   +/-   ##
========================================
  Coverage    42.77%   42.77%           
========================================
  Files          101      101           
  Lines        35944    35944           
========================================
  Hits         15376    15376           
  Misses       20568    20568           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data'

Translated to English:

Δ = absolute <relative> (impact), ø = not affected, ? = missing data'
Powered by Codecov. Last update ce47d5c...48c9fc7. Read the comment docs.

TRANS_BY_GPT3

[zhouxiaojun2008]

Shi Dashen, I have some doubts as follows:

This modification is based on the fact that the callback from ts outputs a complete frame of data. Therefore, here we directly send the entire frame of data at once. However, there may be a problem, for example, in the case of zerolatecy, where a frame may have multiple slices. The first slice is 00 00 00 01 xx, and the following slices are also 00 00 01 xx. If we send them all at once, the start code of the first slice is removed, but the start code of the following slices is not removed. This may pose a potential risk. Will there be any issues when this data is sent to SRS? Additionally, I will attach two images.

My modification is as follows:
`std::vectorstd::string vec_nalus;

// send each frame.
while (!avs_ptr->empty()) {
    char* frame = NULL;
    int frame_size = 0;
    if ((err = _avc_ptr->annexb_demux(avs_ptr, &frame, &frame_size)) != srs_success) {
        return srs_error_wrap(err, "demux annexb");
    }

    // 5bits, 7.3.1 NAL unit syntax,
    // ISO_IEC_14496-10-AVC-2003.pdf, page 44.
    //  7: SPS, 8: PPS, 5: I Frame, 1: P Frame
    SrsAvcNaluType nal_unit_type = (SrsAvcNaluType)(frame[0] & 0x1f);
    //srs_trace("frame size:%d,type:%d", frame_size, nal_unit_type);
    // ignore the nalu type sps(7), pps(8), aud(9)
    switch (nal_unit_type) {
        case SrsAvcNaluTypeSPS: {
            std::string sps;
            if ((err = _avc_ptr->sps_demux(frame, frame_size, sps)) != srs_success) {
                return srs_error_wrap(err, "demux sps");
            }

            if (_h264_sps == sps) {
                continue;
            }
            _h264_sps_changed = true;
            _h264_sps = sps;

            if ((err = write_h264_sps_pps(dts, pts)) != srs_success) {
                return srs_error_wrap(err, "write sps/pps");
            }
            continue;
        }
        case SrsAvcNaluTypePPS: {
            std::string pps;
            if ((err = _avc_ptr->pps_demux(frame, frame_size, pps)) != srs_success) {
                return srs_error_wrap(err, "demux pps");
            }

            if (_h264_pps == pps) {
                continue;
            }
            _h264_pps_changed = true;
            _h264_pps = pps;

            if ((err = write_h264_sps_pps(dts, pts)) != srs_success) {
                return srs_error_wrap(err, "write sps/pps");
            }
            continue;
        }
        case SrsAvcNaluTypeAccessUnitDelimiter:
        case SrsAvcNaluTypeSEI: {
            continue;
        }
        default: {
            // ibp frame

if (!avs_ptr->empty()) { // If it is not empty, it means it is a multi-slice
vec_nalus.push_back(std::string(frame, frame_size));
}
else {
if (vec_nalus.empty()) {
if ((err = write_h264_ipb_frame(frame, frame_size, dts, pts)) != srs_success)
return srs_error_wrap(err, "write h264 ipb frame");
}
else {
vec_nalus.push_back(std::string(frame, frame_size));
if ((err = write_h264_ipb_frame(vec_nalus, dts, pts)) != srs_success)
return srs_error_wrap(err, "write h264 ipb slice frame");
}
_last_live_ts = now_ms();
}
continue;
}
}
}`

TRANS_BY_GPT3