m3u8是蘋果公司推出的視頻播放標準笑撞，是m3u的一種默终，只是編碼格式采用的是UTF-8兼蜈。
存儲的信息類似于：

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-ALLOW-CACHE:YES
#EXT-X-TARGETDURATION:6
#EXTINF:5,
abc_0123.ts
#EXTINF:5,
abc_0124.ts
#EXTINF:5,
abc_0125.ts
#EXT-X-ENDLIST

m3u8準確來說是一種索引文件历等，使用m3u8文件實際上是通過它來解析對應(yīng)的放在服務(wù)器上的視頻網(wǎng)絡(luò)地址，從而實現(xiàn)在線播放滥玷。
在flutter中，要下載m3u8的視頻巍棱，實際上是要將m3u8中列出的abc_0123.ts視頻文件全部下載下來惑畴，再合成一個mp4文件。
需要用到幾個插件

flutter_hls_parser: ^2.0.0  // 解析m3u8文件
ffmpeg_kit_flutter: 4.5.1-LTS  // 合成mp4文件
image_gallery_saver: ^1.7.1  // 保存到手機相冊

具體代碼如下

import "dart:io";

import "package:bot_toast/bot_toast.dart";
import "package:dio/dio.dart";
import "package:ffmpeg_kit_flutter/ffmpeg_kit.dart";
import "package:ffmpeg_kit_flutter/ffmpeg_session.dart";
import "package:ffmpeg_kit_flutter/log.dart";
import "package:ffmpeg_kit_flutter/statistics.dart";
import "package:flutter/material.dart";
import "package:flutter_hls_parser/flutter_hls_parser.dart";
import "package:image_gallery_saver/image_gallery_saver.dart";
import "package:path_provider/path_provider.dart";

class DownloadM3U8Util {
  DownloadM3U8Util._();

  static final DownloadM3U8Util instance = DownloadM3U8Util._();
  List<String> downLoadUrl = [];

  // 傳入m3u8下載地址
  Future<void> downloadM3u8(String url) async {
    debugPrint("DownloadUtil, _url=$url");
    if (downLoadUrl.contains(url)) {
      print("已進入下載隊列");
      return;
    }
    final String savePath = await _getSavePath();  // 存儲路徑
   
    downLoadUrl.add(url);
    final String host = url.substring(0, url.lastIndexOf("/"));
    final String m3u8FileName = url.substring(url.lastIndexOf("/") + 1); // m3u8文件名帶后綴.  xxx.m3u8
    final String m3u8Path = "$savePath/$m3u8FileName"; // m3u8保存絕對路徑  /abc/../xxx.m3u8
    final String m3u8Name = m3u8FileName.split(".").first; // m3u8文件名不帶后綴  xxx

    final Response response = await Dio().download(url, m3u8Path);
    if (response.statusCode != 200) {
      print("下載 m3u8 失敗 _url=$url");
      downLoadUrl.remove(url);
      return;
    }
    // video文件夾不存在則創(chuàng)建
    Directory directory = Directory("$savePath/video/");
    if (!directory.existsSync()) {
      directory.createSync();
    }

    HlsPlaylist playList;
    try {
      playList = await HlsPlaylistParser.create()
          .parse(Uri.parse(url), await File(m3u8Path).readAsLines());
    } on ParserException catch (e) {
      print(e);
    }

    if (playList is HlsMediaPlaylist) {
      // 讀取m3u8文件的URL信息
      final mediaPlaylistUrls = playList.segments.map((it) => it.url);
      for (var value in mediaPlaylistUrls) {
        // value  oux02488.ts
        String tsUrl = "$host/$value";
        File file = File("$savePath/$value");
        if (!file.existsSync()) {
          file.create();
        }
        print("下載ts地址 url=$tsUrl航徙， file.path=${file.path}");
        Response _response = await Dio().download(tsUrl, file.path);
        if (_response.statusCode != 200) {
          downLoadUrl.remove(url);
          return;
        }
      }
      print("已下載完所有ts視頻");
      String cmd = '-allowed_extensions ALL -i $m3u8Path  "$savePath/video/$m3u8Name.mp4"';

      ///合并ts為mp4
      FFmpegKit.executeAsync(cmd, (FFmpegSession session) {
        BotToast.showText(text: "下載成功");
        downLoadUrl.remove(url);
        // 保存到相冊
        ImageGallerySaver.saveFile("$savePath/video/$m3u8Name.mp4").then((value) {
          // 刪除臨時路徑的文件
          File file = File("$savePath/video/$m3u8Name.mp4");
          file.deleteSync();
        });
      });
    }
  }

  /// 獲取存儲路徑
  static Future<String> _getSavePath() async {
    final directory = Platform.isAndroid
        ? await getExternalStorageDirectory()
        : await getApplicationDocumentsDirectory();
    return directory.path;
  }
}