How to implement HLS protocol using Go language

HLS, HTTP Live Streaming, is a video streaming protocol proposed by Apple. In other platforms, the HLS protocol can also be used to transmit video streams. For example, on the Android platform, Google ExoPlayer also supports playing HLS video streams. The HLS protocol mainly cuts the original video file into a series of small files. These small files are called segments. These fragments need to be encoded into the corresponding encoding format, such as H.264. The client will obtain this series of fragments through the HTTP protocol. When the client gets a fragment, it starts playing the fragment. When this segment is played, the client will obtain the next segment and play it. In this way, a complete video can be played.

The Go language is a very simple, efficient, and very suitable language for concurrent programming. In the Go language, implementing the HLS protocol is very simple. In this article, we will introduce how to implement the HLS protocol using the Go language.

First, we need to build some basic HTTP server code. This part of the code is very simple. We only need to create an HTTP server with a listening address and port. When the client accesses the server, it can obtain a file on the server and return the contents of the file to the client.

package main

import (
    "io/ioutil"
    "net/http"
)

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        data, _ := ioutil.ReadFile("example.mp4")
        w.Write(data)
    })

    http.ListenAndServe(":8000", nil)
}

In this code, we create an HTTP server listening on port 8000. When a client accesses this server, it returns the contents of the example.mp4 file to the client.

Next, we need to write some code to implement slicing of the HLS protocol. This part of the code is very critical. The core of the entire HLS protocol is to cut a video file into many small fragments, and then transmit these fragments to the client through the HTTP protocol. We need to write code to implement this functionality.

package main

import (
    "bytes"
    "fmt"
    "io/ioutil"
    "net/http"
    "os"
    "os/exec"
    "path/filepath"
)

func main() {

    // 执行 ffmpeg 命令将 example.mp4 文件切割成小的分片
    segmentDir := "segment"
    if _, err := os.Stat(segmentDir); os.IsNotExist(err) {
        os.Mkdir(segmentDir, os.ModePerm)
    }

    cmd := exec.Command("ffmpeg", "-i", "example.mp4", "-profile:v", "baseline", "-level", "3.0", "-start_number", "0", "-hls_time", "10", "-hls_list_size", "0", "-f", "hls", filepath.Join(segmentDir, "out.m3u8"))
    err := cmd.Run()
    if err != nil {
        fmt.Println("exec cmd failed")
        panic(err)
    }

    // 启动 HTTP 服务器用于客户端获取切片文件
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {

        if r.URL.Path == "/out.m3u8" {

            // 获取 m3u8 文件的内容，此文件是一个播放列表，里面包含了可以播放的 ts 文件的序列
            data, _ := ioutil.ReadFile(filepath.Join(segmentDir, "out.m3u8"))
            w.Write(data)

        } else if len(r.URL.Path) > len("/segment/") && r.URL.Path[0:9] == "/segment/" {

            // 如果客户端要求播放某个 ts 文件，那么我们就需要从本地文件系统读取这个文件并且返回给客户端
            data, _ := ioutil.ReadFile(filepath.Join(segmentDir, r.URL.Path[1:]))
            http.ServeContent(w, r, "", 0, bytes.NewReader(data))

        }

    })

    // 启动 HTTP 服务器
    http.ListenAndServe(":8000", nil)
}

In this code, we mainly use the os/exec package of Go language to execute external commands. It will start a Shell process and execute the corresponding command. In this example, we use the ffmpeg command to cut the example.mp4 file into multiple small segments, and save these segments to a segment directory. Then, we can provide these fragments to the client for playback through the HTTP protocol.

When the client requests /out.m3u8, we will directly return the list of shards to the client. When the client requests /segment/xxx, we need to read the corresponding segment on the local file system and return it to the client.

Finally, we successfully implemented the HLS protocol using Go language. The simplicity and efficiency of the Go language are very suitable for such application scenarios that require high concurrency and high throughput. If you get a chance, be sure to try implementing the HLS protocol in Go.

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