add mpes frame extractor

2025-09-26 19:41:18 +08:00 · 2020-12-14 08:52:44 +08:00
parent 5e0398ae94
commit 4508302351
1 changed files with 126 additions and 0 deletions
--- a/protos/rtp/mpes_frame_extractor.go
+++ b/protos/rtp/mpes_frame_extractor.go
@@ -0,0 +1,126 @@
+// Copyright (c) 2019,CAOHONGJU All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package rtp
+
+import (
+	"fmt"
+
+	"github.com/cnotch/tomatox/av/aac"
+)
+
+type mpesFrameExtractor struct {
+	w           FrameWriter
+	sizeLength  int
+	indexLength int
+	extractFunc func(packet *Packet) error
+}
+
+// NewMPESFrameExtractor 实例化 MPES 帧提取器
+func NewMPESFrameExtractor(w FrameWriter, sizeLength, indexLength int) FrameExtractor {
+	fe := &mpesFrameExtractor{
+		w:           w,
+		sizeLength:  sizeLength,
+		indexLength: indexLength,
+	}
+	switch sizeLength + indexLength {
+	case 8:
+		fe.extractFunc = fe.extractFor1ByteAUHeader
+	case 16:
+		fe.extractFunc = fe.extractFor2ByteAUHeader
+	default:
+		panic(fmt.Sprintf("not supported au_header size(%d,%d)", sizeLength, indexLength))
+	}
+	return fe
+}
+
+//  以下是当 sizelength=13;indexlength=3;indexdeltalength=3 时
+//  Au-header = 13+3 bits(2byte) 的示意图
+// 	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+//  |       AU-headers-length     |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+//  |       AU-header(1)          |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+//  |       AU-header(2)          |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+//  |       ...                   |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+//  |       AU-header(n)          |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+//  |       pading bits           |
+//  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
+// 当 sizelength=6;indexlength=2;indexdeltalength=2 时
+// 单帧封装时，rtp payload的长度 = AU-header-lengths(两个字节) + AU-header(6+2) + AU的长度
+func (fe *mpesFrameExtractor) Extract(packet *Packet) (err error) {
+	return fe.extractFunc(packet)
+}
+
+func (fe *mpesFrameExtractor) extractFor2ByteAUHeader(packet *Packet) (err error) {
+	payload := packet.Payload()
+
+	// AU-headers-length 2bytes
+	auHeadersLength := uint16(0) | (uint16(payload[0]) << 8) | uint16(payload[1])
+	// AU-headers-length / 16
+	auHeadersCount := auHeadersLength >> 4
+	// AU 帧数据偏移位置
+	framesPayloadOffset := 2 + int(auHeadersCount)<<1
+
+	auHeaders := payload[2:framesPayloadOffset]
+	framesPayload := payload[framesPayloadOffset:]
+	frameTimeStamp := packet.Timestamp
+	for i := 0; i < int(auHeadersCount); i++ {
+		auHeader := uint16(0) | (uint16(payload[0]) << 8) | uint16(payload[1])
+		frameSize := auHeader >> fe.indexLength
+		frame := &Frame{
+			FrameAudio,
+			frameTimeStamp,
+			framesPayload[:frameSize],
+		}
+		if err = fe.w.Write(frame); err != nil {
+			return
+		}
+
+		// 下一帧
+		auHeaders = auHeaders[2:]
+		framesPayload = framesPayload[frameSize:]
+		frameTimeStamp += aac.SamplesPerFrame // 每帧采样数
+	}
+
+	return
+}
+
+func (fe *mpesFrameExtractor) extractFor1ByteAUHeader(packet *Packet) (err error) {
+	payload := packet.Payload()
+
+	// AU-headers-length 2bytes
+	auHeadersLength := uint16(0) | (uint16(payload[0]) << 8) | uint16(payload[1])
+	// AU-headers-length / 16
+	auHeadersCount := auHeadersLength >> 4
+	// AU 帧数据偏移位置
+	framesPayloadOffset := 2 + int(auHeadersCount)
+
+	auHeaders := payload[2:framesPayloadOffset]
+	framesPayload := payload[framesPayloadOffset:]
+	frameTimeStamp := packet.Timestamp
+	for i := 0; i < int(auHeadersCount); i++ {
+		auHeader := payload[0]
+		frameSize := auHeader >> fe.indexLength
+		frame := &Frame{
+			FrameAudio,
+			frameTimeStamp,
+			framesPayload[:frameSize],
+		}
+		if err = fe.w.Write(frame); err != nil {
+			return
+		}
+
+		// 下一帧
+		auHeaders = auHeaders[1:]
+		framesPayload = framesPayload[frameSize:]
+		frameTimeStamp += aac.SamplesPerFrame // 每帧采样数
+	}
+
+	return
+}