使用go-mpd解析和生成MPEG-DASH清单文件

MPEG-DASH（Dynamic Adaptive Streaming over HTTP）是一种流行的自适应流媒体传输协议，其核心是MPD（Media Presentation Description）清单文件。在Go语言中，我们可以使用go-mpd库来处理MPD文件。

go-mpd库简介

go-mpd是一个用于解析和生成MPEG-DASH MPD清单文件的Go语言库，它提供了完整的MPD数据结构表示和XML序列化/反序列化功能。

安装

go get github.com/zencoder/go-mpd/mpd

基本用法

1. 解析MPD文件

package main

import (
	"encoding/xml"
	"fmt"
	"io/ioutil"
	"os"

	"github.com/zencoder/go-mpd/mpd"
)

func main() {
	// 读取MPD文件
	data, err := ioutil.ReadFile("example.mpd")
	if err != nil {
		fmt.Printf("读取文件错误: %v\n", err)
		os.Exit(1)
	}

	// 解析MPD
	var m mpd.MPD
	if err := xml.Unmarshal(data, &m); err != nil {
		fmt.Printf("解析MPD错误: %v\n", err)
		os.Exit(1)
	}

	// 输出基本信息
	fmt.Printf("MPD版本: %s\n", m.Profiles)
	fmt.Printf("媒体时长: %s\n", m.MediaPresentationDuration)
	fmt.Printf("包含 %d 个Period\n", len(m.Periods))
}

2. 生成MPD文件

package main

import (
	"encoding/xml"
	"fmt"
	"os"
	"time"

	"github.com/zencoder/go-mpd/mpd"
)

func main() {
	// 创建MPD对象
	m := mpd.NewMPD(mpd.DYNAMIC_TYPE)
	m.Profiles = "urn:mpeg:dash:profile:isoff-on-demand:2011"
	m.MinBufferTime = "PT1.5S"
	m.MediaPresentationDuration = "PT30M0S"

	// 添加Period
	period := &mpd.Period{
		ID:    "period1",
		Start: "PT0S",
	}

	// 添加AdaptationSet
	adaptationSet := &mpd.AdaptationSet{
		ContentType:  "video",
		MimeType:     "video/mp4",
		SegmentAlignment: true,
		StartWithSAP: 1,
	}

	// 添加Representation
	representation := &mpd.Representation{
		ID:        "video1",
		Bandwidth: 1000000,
		Width:     640,
		Height:    360,
		FrameRate: "30/1",
		Codecs:    "avc1.42c01e",
	}

	// 添加SegmentTemplate
	segmentTemplate := &mpd.SegmentTemplate{
		Timescale:      90000,
		Media:          "video-$Bandwidth$-$Number$.m4s",
		Initialization: "video-$Bandwidth$-init.mp4",
		StartNumber:    1,
		Duration:       90000,
	}

	representation.SegmentTemplate = segmentTemplate
	adaptationSet.Representations = append(adaptationSet.Representations, representation)
	period.AdaptationSets = append(period.AdaptationSets, adaptationSet)
	m.Periods = append(m.Periods, period)

	// 生成XML
	output, err := xml.MarshalIndent(m, "", "  ")
	if err != nil {
		fmt.Printf("生成XML错误: %v\n", err)
		os.Exit(1)
	}

	// 添加XML头
	output = []byte(xml.Header + string(output))

	// 写入文件
	err = os.WriteFile("output.mpd", output, 0644)
	if err != nil {
		fmt.Printf("写入文件错误: %v\n", err)
		os.Exit(1)
	}

	fmt.Println("MPD文件生成成功")
}

高级功能

1. 处理动态MPD

// 设置MPD为动态类型
m := mpd.NewMPD(mpd.DYNAMIC_TYPE)
m.AvailabilityStartTime = time.Now().Format(time.RFC3339)
m.PublishTime = time.Now().Format(time.RFC3339)
m.MinimumUpdatePeriod = "PT5S"
m.TimeShiftBufferDepth = "PT5M"

2. 添加多个Representation

// 添加多个码率层
bitrates := []struct {
	id       string
	width    int
	height   int
	bandwidth uint64
}{
	{"video1", 640, 360, 500000},
	{"video2", 854, 480, 1000000},
	{"video3", 1280, 720, 2500000},
}

for _, br := range bitrates {
	rep := &mpd.Representation{
		ID:        br.id,
		Bandwidth: br.bandwidth,
		Width:     br.width,
		Height:    br.height,
		Codecs:    "avc1.42c01e",
	}
	adaptationSet.Representations = append(adaptationSet.Representations, rep)
}

3. 处理音频轨道

// 添加音频AdaptationSet
audioSet := &mpd.AdaptationSet{
	ContentType:  "audio",
	MimeType:     "audio/mp4",
	Lang:         "en",
	SegmentAlignment: true,
}

audioRep := &mpd.Representation{
	ID:        "audio1",
	Bandwidth: 128000,
	Codecs:    "mp4a.40.2",
	AudioSamplingRate: 44100,
}

audioTemplate := &mpd.SegmentTemplate{
	Timescale:      44100,
	Media:          "audio-$Bandwidth$-$Number$.m4s",
	Initialization: "audio-$Bandwidth$-init.mp4",
	StartNumber:    1,
	Duration:       132300, // 3秒
}

audioRep.SegmentTemplate = audioTemplate
audioSet.Representations = append(audioSet.Representations, audioRep)
period.AdaptationSets = append(period.AdaptationSets, audioSet)

注意事项

1. go-mpd库支持MPD规范的多个版本，但需要确保生成的MPD符合目标播放器的要求
2. 对于实时流媒体，需要正确处理时间相关属性和动态更新
3. 确保SegmentTemplate中的媒体片段路径与实际存储路径一致
4. 多码率自适应时，各Representation的SegmentTemplate配置需要一致

go-mpd库提供了完整的MPD处理能力，可以满足大多数DASH流媒体应用的需求。通过合理配置Period、AdaptationSet和Representation结构，可以构建出适合各种场景的MPD清单文件。