mirror of
https://gitee.com/xia-chu/ZLMediaKit.git
synced 2026-05-06 10:57:50 +08:00
275 lines
8.8 KiB
C++
275 lines
8.8 KiB
C++
/*
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* Copyright (c) 2016-present The ZLMediaKit project authors. All Rights Reserved.
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*
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* This file is part of ZLMediaKit(https://github.com/ZLMediaKit/ZLMediaKit).
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*
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* Use of this source code is governed by MIT-like license that can be found in the
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* LICENSE file in the root of the source tree. All contributing project authors
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* may be found in the AUTHORS file in the root of the source tree.
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*/
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#include "MP2VRtp.h"
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#include "Common/config.h"
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namespace mediakit {
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// ======================== MP2VRtpDecoder ========================
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MP2VRtpDecoder::MP2VRtpDecoder() {
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obtainFrame();
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}
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void MP2VRtpDecoder::obtainFrame() {
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_frame = FrameImp::create<MP2VFrame>();
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}
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bool MP2VRtpDecoder::inputRtp(const RtpPacket::Ptr &rtp, bool key_pos) {
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auto seq = rtp->getSeq();
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auto last_gop_dropped = _gop_dropped;
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bool is_gop_start = decodeRtp(rtp);
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if (!_gop_dropped && seq != (uint16_t)(_last_seq + 1) && _last_seq) {
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_gop_dropped = true;
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WarnL << "start drop mp2v gop, last seq:" << _last_seq << ", rtp:\r\n" << rtp->dumpString();
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}
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_last_seq = seq;
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return is_gop_start && !last_gop_dropped;
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}
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/**
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* RFC 2250 MPEG Video-specific header (4 bytes):
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*
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* 0 1 2 3
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* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* | MBZ |T| TR |AN|N|S|B|E| P | | BFC | | FFC |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* FBV FFV
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*
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* T: MPEG-2 specific header extension present (1 bit)
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* TR: Temporal Reference (10 bits)
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* AN: Active N bit (1 bit)
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* N: New picture header (1 bit)
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* S: Sequence-header-present (1 bit)
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* B: Beginning-of-slice (1 bit)
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* E: End-of-slice (1 bit)
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* P: Picture-Type (3 bits): I(1), P(2), B(3), D(4)
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* FBV: full_pel_backward_vector (1 bit)
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* BFC: backward_f_code (3 bits)
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* FFV: full_pel_forward_vector (1 bit)
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* FFC: forward_f_code (3 bits)
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*/
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bool MP2VRtpDecoder::decodeRtp(const RtpPacket::Ptr &rtp) {
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auto payload_size = rtp->getPayloadSize();
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if (payload_size <= (ssize_t)kMP2VHeaderSize) {
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// 负载太小，不包含有效数据
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return false;
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}
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auto payload = rtp->getPayload();
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auto stamp = rtp->getStampMS();
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auto seq = rtp->getSeq();
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// 解析 RFC 2250 MPEG Video-specific header
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bool t_bit = (payload[0] >> 2) & 0x01;
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// uint16_t temporal_ref = ((payload[0] & 0x03) << 8) | payload[1];
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// bool seq_header_present = (payload[2] >> 5) & 0x01;
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// bool begin_of_slice = (payload[2] >> 4) & 0x01;
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// bool end_of_slice = (payload[2] >> 3) & 0x01;
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uint8_t picture_type = (payload[2] & 0x07);
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// 如果 T bit 置位，还有 4 字节的 MPEG-2 扩展头需要跳过
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size_t header_size = kMP2VHeaderSize + (t_bit ? 4 : 0);
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if (payload_size <= (ssize_t)header_size) {
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return false;
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}
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auto es_data = payload + header_size;
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auto es_size = payload_size - header_size;
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// 检查是否为新帧（时间戳变化）
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if (!_frame->_buffer.empty() && stamp != _frame->_pts) {
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// 时间戳变化，输出上一帧
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outputFrame(rtp);
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}
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if (_frame->_buffer.empty()) {
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// 新帧开始
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_frame->_pts = stamp;
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_drop_flag = false;
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_picture_type = picture_type;
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}
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if (_drop_flag) {
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return false;
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}
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// 检测 seq 不连续，丢弃当前帧
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if (!_frame->_buffer.empty() && seq != (uint16_t)(_last_seq + 1) && _last_seq) {
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_drop_flag = true;
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_frame->_buffer.clear();
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return false;
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}
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// 追加 ES 数据
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_frame->_buffer.append((char *)es_data, es_size);
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// RTP mark bit 标识帧结束
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if (rtp->getHeader()->mark) {
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outputFrame(rtp);
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return _picture_type == 1; // I-Picture
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}
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return false;
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}
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void MP2VRtpDecoder::outputFrame(const RtpPacket::Ptr &rtp) {
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if (_frame->_buffer.empty()) {
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return;
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}
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// 生成 DTS（MPEG-2 有 B 帧，PTS 和 DTS 不一定相同）
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_dts_generator.getDts(_frame->_pts, _frame->_dts);
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bool is_key = _frame->keyFrame();
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if (is_key && _gop_dropped) {
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_gop_dropped = false;
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InfoL << "new mp2v gop received, rtp:\r\n" << rtp->dumpString();
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}
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if (!_gop_dropped) {
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RtpCodec::inputFrame(_frame);
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}
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obtainFrame();
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}
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// ======================== MP2VRtpEncoder ========================
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bool MP2VRtpEncoder::hasSequenceHeader(const uint8_t *data, size_t size) {
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// 查找 sequence header start code: 00 00 01 B3
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for (size_t i = 0; i + 3 < size; ++i) {
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if (data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01 && data[i + 3] == 0xB3) {
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return true;
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}
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}
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return false;
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}
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void MP2VRtpEncoder::parsePictureInfo(const uint8_t *data, size_t size) {
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_temporal_ref = 0;
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_picture_type = 0;
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_fbv = 0;
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_bfc = 0;
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_ffv = 0;
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_ffc = 0;
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_has_seq_header = hasSequenceHeader(data, size);
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// 查找 picture start code: 00 00 01 00
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for (size_t i = 0; i + 5 < size; ++i) {
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if (data[i] == 0x00 && data[i + 1] == 0x00 && data[i + 2] == 0x01 && data[i + 3] == 0x00) {
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// temporal_reference: 10 bits, picture_coding_type: 3 bits
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_temporal_ref = (data[i + 4] << 2) | ((data[i + 5] >> 6) & 0x03);
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_picture_type = (data[i + 5] >> 3) & 0x07;
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// 解析 motion vector codes (vbv_delay 之后)
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// picture header: temporal_reference(10) + picture_coding_type(3) + vbv_delay(16)
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if (i + 8 < size) {
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uint8_t extra_byte = data[i + 8];
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if (_picture_type == 2 /* P */ || _picture_type == 3 /* B */) {
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// full_pel_forward_vector(1) + forward_f_code(3)
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_ffv = (extra_byte >> 2) & 0x01;
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_ffc = ((extra_byte & 0x03) << 1);
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if (i + 9 < size) {
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_ffc |= (data[i + 9] >> 7) & 0x01;
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}
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}
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if (_picture_type == 3 /* B */) {
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// full_pel_backward_vector(1) + backward_f_code(3) 紧跟在 forward 之后
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if (i + 9 < size) {
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_fbv = (data[i + 9] >> 6) & 0x01;
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_bfc = (data[i + 9] >> 3) & 0x07;
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}
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}
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}
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return;
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}
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}
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}
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void MP2VRtpEncoder::buildMpvHeader(uint8_t *buf, const uint8_t *data, size_t size,
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bool is_begin_of_slice, bool is_end_of_slice) {
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// RFC 2250 Section 3.4
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// Byte 0: MBZ(5) + T(1) + TR high 2 bits
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// T = 0 (不发送 MPEG-2 扩展头)
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buf[0] = (_temporal_ref >> 8) & 0x03;
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// Byte 1: TR low 8 bits
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buf[1] = _temporal_ref & 0xFF;
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// Byte 2: AN(1) + N(1) + S(1) + B(1) + E(1) + P(3)
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uint8_t byte2 = 0;
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// AN = 0, N = 0
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if (_has_seq_header) {
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byte2 |= 0x20; // S bit
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}
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if (is_begin_of_slice) {
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byte2 |= 0x10; // B bit
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}
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if (is_end_of_slice) {
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byte2 |= 0x08; // E bit
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}
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byte2 |= (_picture_type & 0x07);
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buf[2] = byte2;
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// Byte 3: FBV(1) + BFC(3) + FFV(1) + FFC(3)
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buf[3] = ((_fbv & 0x01) << 7) | ((_bfc & 0x07) << 4) | ((_ffv & 0x01) << 3) | (_ffc & 0x07);
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}
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bool MP2VRtpEncoder::inputFrame(const Frame::Ptr &frame) {
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auto ptr = (const uint8_t *)frame->data() + frame->prefixSize();
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auto size = frame->size() - frame->prefixSize();
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if (size == 0) {
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return false;
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}
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// 解析帧信息（picture type, temporal reference 等）
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parsePictureInfo(ptr, size);
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bool is_key = frame->keyFrame();
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auto max_payload = getRtpInfo().getMaxSize() - kMP2VHeaderSize;
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size_t offset = 0;
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while (offset < size) {
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bool is_first = (offset == 0);
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size_t payload_size;
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bool is_last;
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if (size - offset <= max_payload) {
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payload_size = size - offset;
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is_last = true;
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} else {
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payload_size = max_payload;
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is_last = false;
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}
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// 构建 MPEG Video-specific header
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uint8_t mpv_header[kMP2VHeaderSize];
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buildMpvHeader(mpv_header, ptr + offset, payload_size, is_first, is_last);
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// 创建 RTP 包：MPEG header + ES data
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auto rtp = getRtpInfo().makeRtp(TrackVideo, nullptr, kMP2VHeaderSize + payload_size, is_last, frame->pts());
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auto rtp_payload = rtp->getPayload();
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// 写入 MPEG Video-specific header
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memcpy(rtp_payload, mpv_header, kMP2VHeaderSize);
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// 写入 ES 数据
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memcpy(rtp_payload + kMP2VHeaderSize, ptr + offset, payload_size);
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// 输入到 RTP 环形缓存
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RtpCodec::inputRtp(rtp, is_key && is_first);
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offset += payload_size;
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}
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return true;
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}
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} // namespace mediakit
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