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基础版本,解析ps内存零拷贝
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‎README.md

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# streams
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轻便的gb28181协议中的rtp+ps格式视频流的封装和解析
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## packet
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packet实现ps的相关封装和解析,
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### example/dec
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截取了部分ps封装码流，通过`RtpParsePacket`进行解析，验证
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```golang
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// ps + system + map + sps + pps
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0x00, 0x00, 0x01, 0xba, 0x5e, 0xee, 0x05, 0x55, 0x74, 0x01, 0x0e, 0xb3, 0x37, 0xfe, 0xff, 0xff,
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0x00, 0xeb, 0xc1, 0x62, 0x00, 0x00, 0x01, 0xbb, 0x00, 0x12, 0x87, 0x59, 0x9b, 0x04, 0xe1, 0x7f,
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0xe0, 0xe0, 0x80, 0xc0, 0xc0, 0x08, 0xbd, 0xe0, 0x80, 0xbf, 0xe0, 0x80, 0x00, 0x00, 0x01, 0xbc,
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0x00, 0x5a, 0xfa, 0xff, 0x00, 0x24, 0x40, 0x0e, 0x48, 0x4b, 0x01, 0x00, 0x13, 0x37, 0xc7, 0x3e,
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0xa7, 0x9f, 0x00, 0xff, 0xff, 0xff, 0x41, 0x12, 0x48, 0x4b, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
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0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x00, 0x2c, 0x1b, 0xe0, 0x00, 0x28,
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0x42, 0x0e, 0x07, 0x10, 0x10, 0xea, 0x07, 0x80, 0x04, 0x38, 0x11, 0x10, 0xc0, 0x00, 0x1c, 0x21,
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0x44, 0x0a, 0x00, 0x00, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x2a, 0x0a, 0x7f, 0xff,
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0x00, 0x00, 0x07, 0x08, 0x1f, 0xfe, 0xf0, 0x87, 0x0c, 0x9a, 0x36, 0x23, 0x00, 0x00, 0x01, 0xe0,
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0x00, 0x26, 0x8c, 0x80, 0x07, 0x27, 0xbb, 0x81, 0x55, 0x5d, 0xff, 0xfc, 0x00, 0x00, 0x00, 0x01,
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0x67, 0x4d, 0x00, 0x2a, 0x96, 0x35, 0x40, 0xf0, 0x04, 0x4f, 0xcb, 0x37, 0x01, 0x01, 0x01, 0x40,
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0x00, 0x01, 0xc2, 0x00, 0x00, 0x57, 0xe4, 0x01, 0x00, 0x00, 0x01, 0xe0, 0x00, 0x0e, 0x8c, 0x00,
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0x03, 0xff, 0xff, 0xfc, 0x00, 0x00, 0x00, 0x01, 0x68, 0xee, 0x3c, 0x80, 0x00, 0x00, 0x01, 0xe0,
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0x00, 0x0e, 0x8c, 0x00, 0x02, 0xff, 0xfc, 0x00, 0x00, 0x00, 0x01, 0x06, 0xe5, 0x01, 0x67, 0x80
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```

‎buffer/buffer.go

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package buffer
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import (
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"encoding/binary"
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"io"
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)
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type RawBuffer struct {
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raw []byte
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buffer int
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}
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func (r *RawBuffer) LoadBuffer(data []byte) {
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r.raw = data
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r.buffer = len(r.raw)
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}
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func (r *RawBuffer) Skip(length int) error {
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if err := r.checkLen(length); err != nil {
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return err
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}
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r.skip(length)
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return nil
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}
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func (r *RawBuffer) Uint8() (uint8, error) {
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if err := r.checkLen(1); err != nil {
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return 0, err
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}
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res := r.raw[0]
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r.skip(1)
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return res, nil
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}
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func (r *RawBuffer) Uint16() (uint16, error) {
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if err := r.checkLen(2); err != nil {
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return 0, err
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}
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res := binary.BigEndian.Uint16(r.raw[:2])
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r.skip(2)
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return res, nil
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}
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func (r *RawBuffer) Uint32() (uint32, error) {
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if err := r.checkLen(4); err != nil {
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return 0, err
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}
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res := binary.BigEndian.Uint32(r.raw[:4])
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r.skip(4)
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return res, nil
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}
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func (r *RawBuffer) Bytes(length int) ([]byte, error) {
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if err := r.checkLen(length); err != nil {
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return nil, err
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}
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res := r.raw[:length]
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r.skip(length)
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return res, nil
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}
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func (r *RawBuffer) checkLen(length int) error {
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if length > r.buffer {
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return io.ErrUnexpectedEOF
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}
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return nil
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}
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func (r *RawBuffer) skip(length int) {
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r.buffer -= length
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r.raw = r.raw[length:]
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}

‎example/dec/main.go

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‎packet/Readme.md

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# PS结构介绍
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### Key Point
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1. 一帧原始数据只能包含一个`ps`, `map`,`sys`(关键帧需要)等结构.当一帧数据超过pes最大的负载时(`0xFFFF`)，则一帧数据可能有多个`pes`结构
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2. rtp结构是包含在封装的最外层，所以 一帧数据或者一片pes结构，可能会被分成多个rtp包
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3. 各个结构中可能都有扩充字段，在解析的时候可以通过扩充字段来解析到表示的长度，从而得到真实的原始数据的长度
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| ps | system header | psm | pesv | pesa |
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`pesv`为视频pes包， `pesa`为音频pes包
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**非关键帧的ps包结构一般不包含系统头和PSM**
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针对PSM中流类型的取值如下：
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| 流类型 | 十六进制值|
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|-----------|-----------|
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| MPEG-4 | 0x10 |
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| H.264 | 0x1B |
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| SVAC | 0x80 |
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| G.711 | 0x90 |
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| G.722.1 | 0x92 |
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| G.723.1 | 0x93 |
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| G.729 | 0x99 |
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| SVAC 音频 | 0x9B |
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具体可以参看`ISO/IEC 13818-1:2000`
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### 各个结构的头字段的说明
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#### PS
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| 字段名 | 比特位长度 | 含义|
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|------------------|:-----:|----------------------------------------|
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| pack_start_code | 32 | 起始码字段`0x000001BA` 标志为一包的开始 |
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| marker_bit |2|标记位字段2位字段，取值`01`|
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| system_clock_reference_base (32..30) |3|系统时钟参考字段|
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| marker_bit | 1| 标记位字段取值`1` |
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| system_clock_reference_base(29..15) |15|系统时钟参考字段 |
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| marker_bit |1 |标记位字段取值`1` |
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| system_clock_reference_base(14..0) |15|系统时钟参考字段 |
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| marker_bit |1 |标记位字段取值`1`|
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| system_clock_reference_extension |9|系统始终参考字段 |
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| marker_bit |1|标记位字段取值`1`|
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| program_mux_rate |22|节目复合速率字段 |
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| marker_bit |1| 标记記位字段取值`1`|
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| marker_bit |1| 标记位字段取值`1`|
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| reserved |5| 填充字段 |
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| pack_stuffing_length |3 |包填充长度字段|
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#### System
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| 字段名 | 比特位长度 | 含义|
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|------------------|:-----:|----------------------------------------|
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| system_header_start_code | 32| 开始码 `0x000001BB` |
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| header_length |16|該字段後的系統標題的字節長度 |
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| marker_bit |1| 标记位字段取值`1` |
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| rate_bound |22|速率界限字段 |
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| marker_bit |1|标记位字段取值`1`|
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| audio_bound |6| 音频界限字段 |
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| fixed_flag |1|固定标志字段 |
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| CSPS_flag |1|CSPS标志字段 |
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| system_audio_lock_flag |1|系統音频锁定标志字段 |
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| system_video_lock_flag |1| 系統视频锁定标志字段|
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| marker_bit |1| 标记位字段取值`1`|
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| vedio_bound |5| 视频界限字段 |
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| packet_rate_restriction_flag|1 |分组速率限制标记字段|
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| reserved_bits |7| 保留位字段|
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| stream_id |8| 流标志字段 一般`0xe0`指视频，`0xc0`音频|
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| marker_bit |2|取值`11` |
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| P-STD_buffer_bound_scale |1b| P-STD界限比例字段|
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|P-STD_buffer_size_bound |13|P-STD大小界限字段|
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注：可能会有多个stream , 通过stream_id的第一个bit判断是否存在stream
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#### Map
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| 字段名 | 比特位长度 | 含义|
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|------------------|:-----:|----------------------------------------|
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| packet start code |32|映射流起始码标志字段|
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| program stream map length |16|节目流映射长度字段 |
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| current_next_indicator |1|当前下一個指示符字段 |
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| reserved |2|填充字段 |
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| program_stream_map_version|5|节目流映射版本字段 |
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| reserved |7|预留填充字段|
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| marker_bit |1|标记位字段取值`1`|
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| program_stream_info_length |16| 节目流信息长度字段 |
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| elementary_stream_map_length|16|基本流映射长度字段 |
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| stream_type |8| 流类型字段 `0x1b H264`， `0x24 H265`|
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| elementary_stream_id |8|视频取值`0xe0-0xef`，通常为`0xe0`,音频取值`0xc0-0xdf`，通常为`0xc0`|
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| elementary_stream_info_length |16|基本流信息长度字段 |
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| CRC_32 |32| CRC字段|
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#### PES
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| 字段名 | 比特位长度 | 含义|
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|------------------|:-----:|----------------------------------------|
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| packet_start_code_prefix |24| 分组起码码`0x000001` |
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| stream_id |8|流标志字段stream_id，其中0x(C0~DF)指音频，0x(E0~EF)视频|
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| PES_packet_length |16| PES分组长度字段|
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| marker_bit|2| 标志位，`10`|
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| PES_scrambling_control |2|PES加扰控制字段 |
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| PES_priority |1| PES优先级字段 |
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| data_alignment_indicator |1|数据对其指示符字段|
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| copyright |1| 盘权字段|
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| original_or_copy |1| 原始或拷贝字段 |
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| PTS_DTS_flags |2| `PTS DTS`标志字段|
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| ESCR_flag |1|ESCR标志字段|
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| ES_rate_flag |1|ES速率标志字段|
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| DSM_trick_mode_flag |1|DSM特技方式标志字段 |
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| additional_copy_info_flag |1|附加版权信息标志字段 |
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| PES_CRC_flag |1|PES CRC标志字段 |
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| PES_extension_flag|1| PES扩张标志字段 |
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| PES_header_data_length| 8| PES标题数据长度字段 |
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注：后面会根据此长度来填写 pts， dts等

‎packet/common.go

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package packet
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import "errors"
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//
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const (
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UDPTransfer int = 0
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TCPTransferActive int = 1
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TCPTransferPassive int = 2
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LocalCache int = 3
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)
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//
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const (
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StreamTypeH264 = 0x1b
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StreamTypeH265 = 0x24
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StreamTypeAAC = 0x90
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)
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//
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const (
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StreamIDVideo = 0xe0
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StreamIDAudio = 0xc0
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)
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//
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const (
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StartCodePS = 0x000001ba
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StartCodeSYS = 0x000001bb
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StartCodeMAP = 0x000001bc
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HaiKangCode = 0x000001bd
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StartCodeVideo = 0x000001e0
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StartCodeAudio = 0x000001c0
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MEPGProgramEndCode = 0x000001b9
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)
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//... len limit
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const (
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RTPHeaderLength int = 12
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PSHeaderLength int = 14
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SystemHeaderLength int = 18
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MAPHeaderLength int = 24
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PESHeaderLength int = 19
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RtpLoadLength int = 1460
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PESLoadLength int = 0xFFFF
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MAXFrameLen int = 1024 * 1024 * 2
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)
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var (
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ErrNotFoundStartCode = errors.New("not found the need start code flag")
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ErrMarkerBit = errors.New("marker bit value error")
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ErrFormatPack = errors.New("not package standard")
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ErrParsePakcet = errors.New("parse ps packet error")
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)
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/*
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This implement from VLC source code
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notes: https://github.com/videolan/vlc/blob/master/modules/mux/mpeg/bits.h
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*/
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//bitsBuffer bits buffer
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type bitsBuffer struct {
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iSize int
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iData int
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iMask uint8
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pData []byte
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}
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func bitsInit(isize int, buffer []byte) *bitsBuffer {
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bits := &bitsBuffer{
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iSize: isize,
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iData: 0,
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iMask: 0x80,
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pData: buffer,
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}
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if bits.pData == nil {
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bits.pData = make([]byte, isize)
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}
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return bits
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}
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func bitsAlign(bits *bitsBuffer) {
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if bits.iMask != 0x80 && bits.iData < bits.iSize {
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bits.iMask = 0x80
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bits.iData++
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bits.pData[bits.iData] = 0x00
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}
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}
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func bitsWrite(bits *bitsBuffer, count int, src uint64) *bitsBuffer {
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for count > 0 {
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count--
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if ((src >> uint(count)) & 0x01) != 0 {
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bits.pData[bits.iData] |= bits.iMask
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} else {
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bits.pData[bits.iData] &= ^bits.iMask
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}
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bits.iMask >>= 1
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if bits.iMask == 0 {
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bits.iData++
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bits.iMask = 0x80
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}
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}
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return bits
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}

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