M3U8とは？

M3U8 プレイリスト形式と HLS ストリーミングプロトコルの実用ガイドです。

概要

M3U8 は HLS（HTTP Live Streaming）で使われる UTF-8 プレイリスト形式です。通常は動画本体ではなく、セグメント、品質、キー、メタデータを指します。

HLS は Apple が導入し、現在はブラウザ、アプリ、OTT でライブ配信と VOD に広く使われています。

M3U8 の仕組み

1. Server segmentation

The server splits a video into short TS or fMP4 segments and writes an M3U8 index file.

2. M3U8 index

The playlist records segment URLs, playback order, duration, variants, and related metadata.

3. Progressive download

The player downloads segments in order and starts playback before the full video is available.

4. Adaptive bitrate

A master playlist can provide multiple qualities, so the player switches according to network conditions.

M3U8 ファイル構造

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:10
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:9.009,
http://media.example.com/first.ts
#EXTINF:9.009,
http://media.example.com/second.ts
#EXTINF:3.003,
http://media.example.com/third.ts
#EXT-X-ENDLIST

#EXTM3U - file header for an M3U playlist

#EXT-X-VERSION - HLS protocol version

#EXT-X-TARGETDURATION - maximum segment duration

#EXTINF - segment duration and URL

#EXT-X-ENDLIST - marks VOD playlist end

M3U8 vs MP4

M3U8 の利点

Supports live streaming.
Adapts quality to bandwidth.
Starts quickly without downloading the full file.
Works well with CDN caching.
Supports encryption.

M3U8 の制限

Not ideal for local file playback without an HTTP server.
Many files can be harder to manage.
Latency can be higher than direct file playback.
Older devices may need a compatible player.
Saving offline is less simple than MP4.

よくある用途

Live video

Sports, news, events, and game streams.

VOD platforms

Video sites, online education, and OTT libraries.

Mobile apps

Video playback in phone and tablet applications.

M3U8 の使い方

Online playback

Open a direct M3U8 URL in an HLS-capable player such as M3U8 Player.

Download and save

Use an M3U8 downloader to fetch segments and merge them when you have permission.

Format conversion

Use FFmpeg or a converter to create MP4 from an allowed M3U8 source.