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// Copyright 2020, Chef. All rights reserved.
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// https://github.com/q191201771/lal
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//
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// Use of this source code is governed by a MIT-style license
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// that can be found in the License file.
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//
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// Author: Chef (191201771@qq.com)
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package mpegts
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type Frame struct {
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PTS uint64
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DTS uint64
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CC uint8 // continuity_counter of TS Header
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// PID of PES Header
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// 音频 mpegts.PidAudio
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// 视频 mpegts.PidVideo
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Pid uint16
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// stream_id of PES Header
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// 音频 mpegts.StreamIDAudio
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// 视频 mpegts.StreamIDVideo
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Sid uint8
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// 音频 全部为false
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// 视频 关键帧为true，非关键帧为false
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Key bool
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// 音频AAC 格式为2字节ADTS头加raw frame
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// 视频AVC 格式为AnnexB
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Raw []byte
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}
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// @param packet: 188字节大小的TS包，注意，一次Pack对应的多个TSPacket，复用的是一块内存
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//
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type OnTSPacket func(packet []byte)
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// @param frame: 各字段含义见mpegts.Frame结构体定义
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// frame.CC 注意，内部会修改frame.CC的值，外部在调用结束后，可保存CC的值，供下次调用时使用
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// frame.Raw 函数调用结束后，内部不会持有该内存块
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//
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// @param onTSPacket: 注意，一次函数调用，可能对应多次回调
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//
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func PackTSPacket(frame *Frame, onTSPacket OnTSPacket) {
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wpos := 0 // 当前packet的写入位置
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lpos := 0 // 当前帧的处理位置
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rpos := len(frame.Raw) // 当前帧大小
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first := true // 是否为帧的首个packet的标准
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packet := make([]byte, 188)
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for lpos != rpos {
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wpos = 0
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frame.CC++
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// 每个packet都需要添加TS Header
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// -----TS Header----------------
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// sync_byte
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// transport_error_indicator 0
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// payload_unit_start_indicator
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// transport_priority 0
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// PID
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// transport_scrambling_control 0
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// adaptation_field_control
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// continuity_counter
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// ------------------------------
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packet[0] = syncByte // sync_byte
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packet[1] = 0x0
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if first {
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packet[1] = 0x40 // payload_unit_start_indicator
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}
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packet[1] |= uint8((frame.Pid >> 8) & 0x1F) //PID高5位
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packet[2] = uint8(frame.Pid & 0xFF) //PID低8位
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// adaptation_field_control 先设置成无Adaptation
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// continuity_counter
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packet[3] = 0x10 | (frame.CC & 0x0f)
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wpos += 4
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if first {
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if frame.Key {
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// 关键帧的首个packet需要添加Adaptation
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// -----Adaptation-----------------------
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// adaptation_field_length
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// discontinuity_indicator 0
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// random_access_indicator 1
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// elementary_stream_priority_indicator 0
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// PCR_flag 1
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// OPCR_flag 0
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// splicing_point_flag 0
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// transport_private_data_flag 0
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// adaptation_field_extension_flag 0
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// program_clock_reference_base
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// reserved
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// program_clock_reference_extension
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// --------------------------------------
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packet[3] |= 0x20 // adaptation_field_control 设置Adaptation
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packet[4] = 7 // adaptation_field_length
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packet[5] = 0x50 // random_access_indicator + PCR_flag
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packPCR(packet[6:], frame.DTS-delay) // using 6 byte
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wpos += 8
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}
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// 帧的首个packet需要添加PES Header
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// -----PES Header------------
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// packet_start_code_prefix
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// stream_id
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// PES_packet_length
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// '10'
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// PES_scrambling_control 0
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// PES_priority 0
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// data_alignment_indicator 0
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// copyright 0
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// original_or_copy 0
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// PTS_DTS_flags
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// ESCR_flag 0
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// ES_rate_flag 0
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// DSM_trick_mode_flag 0
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// additional_copy_info_flag 0
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// PES_CRC_flag 0
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// PES_extension_flag 0
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// PES_header_data_length
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// ---------------------------
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packet[wpos] = 0x00 // packet_start_code_prefix 24-bits
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packet[wpos+1] = 0x00 //
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packet[wpos+2] = 0x01 //
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packet[wpos+3] = frame.Sid // stream_id
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wpos += 4
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// 计算PES Header中一些字段的值
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// PTS相关
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headerSize := uint8(5)
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flags := uint8(0x80)
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// DTS相关
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if frame.DTS != frame.PTS {
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headerSize += 5
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flags |= 0x40
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}
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pesSize := rpos + int(headerSize) + 3 // PES Header剩余3字节 + PTS/PTS长度 + 整个帧的长度
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if pesSize > 0xFFFF {
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pesSize = 0
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}
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packet[wpos] = uint8(pesSize >> 8) // PES_packet_length
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packet[wpos+1] = uint8(pesSize & 0xFF) //
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packet[wpos+2] = 0x80 // 除了reserve的'10'，其他字段都是0
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packet[wpos+3] = flags // PTS/DTS flag
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packet[wpos+4] = headerSize // PES_header_data_length: PTS+DTS数据长度
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wpos += 5
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// 写入PTS的值
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packPTS(packet[wpos:], flags>>6, frame.PTS+delay)
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wpos += 5
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// 写入DTS的值
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if frame.PTS != frame.DTS {
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packPTS(packet[wpos:], 1, frame.DTS+delay)
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wpos += 5
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}
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first = false
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}
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// 把帧的内容切割放入packet中
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bodySize := 188 - wpos // 当前TS packet，可写入大小
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inSize := rpos - lpos // 整个帧剩余待打包大小
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if bodySize <= inSize {
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// 当前packet写不完这个帧，或者刚好够写完
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copy(packet[wpos:], frame.Raw[lpos:lpos+inSize])
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lpos += bodySize
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} else {
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// 当前packet可以写完这个帧，并且还有空闲空间
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// 此时，真实数据挪最后，中间用0xFF填充到Adaptation中
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// 注意，此时有两种情况
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// 1. 原本有Adaptation
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// 2. 原本没有Adaptation
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stuffSize := bodySize - inSize // 当前TS packet的剩余空闲空间
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if packet[3]&0x20 != 0 {
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// has Adaptation
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base := int(4 + packet[4]) // TS Header + Adaptation
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if wpos > base {
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// 比如有PES Header
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copy(packet[base+stuffSize:], packet[base:wpos])
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}
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wpos = base + stuffSize
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packet[4] += uint8(stuffSize) // adaptation_field_length
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for i := 0; i < stuffSize; i++ {
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packet[base+i] = 0xFF
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}
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} else {
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// no Adaptation
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packet[3] |= 0x20
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base := 4
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if wpos > base {
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copy(packet[base+stuffSize:], packet[base:wpos])
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}
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wpos += stuffSize
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packet[4] = uint8(stuffSize - 1) // adaptation_field_length
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if stuffSize >= 2 {
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// TODO chef 这里是参考nginx rtmp module的实现，为什么这个字节写0而不是0xFF
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packet[5] = 0
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for i := 0; i < stuffSize-2; i++ {
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packet[6+i] = 0xFF
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}
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}
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}
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// 真实数据放在packet尾部
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copy(packet[wpos:], frame.Raw[lpos:lpos+inSize])
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lpos = rpos
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}
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onTSPacket(packet)
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}
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}
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func packPCR(out []byte, pcr uint64) {
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out[0] = uint8(pcr >> 25)
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out[1] = uint8(pcr >> 17)
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out[2] = uint8(pcr >> 9)
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out[3] = uint8(pcr >> 1)
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out[4] = uint8(pcr<<7) | 0x7e
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out[5] = 0
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}
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// 注意，除PTS外，DTS也使用这个函数打包
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func packPTS(out []byte, fb uint8, pts uint64) {
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var val uint64
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out[0] = (fb << 4) | (uint8(pts>>30) & 0x07) | 1
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val = (((pts >> 15) & 0x7FFF) << 1) | 1
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out[1] = uint8(val >> 8)
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out[2] = uint8(val)
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val = ((pts & 0x7FFF) << 1) | 1
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out[3] = uint8(val >> 8)
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out[4] = uint8(val)
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}
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