HLS Player: Test an M3U8 Stream Online

What the player tells you

HLS (HTTP Live Streaming) cuts video into short files and lists them in a text playlist, the .m3u8. A player downloads the playlist, then the segments, one after another, over plain HTTPS. That is why HLS plays in a browser and through a CDN, where RTMP does not.

A master playlist lists several renditions of the same stream at different resolutions and bitrates; the player picks one and switches as the connection changes. A media playlist lists the segments of one rendition. The quality list in the readout shows the renditions of a master playlist; a media playlist has just one.

A live playlist keeps growing and has no end tag; a VOD playlist ends with #EXT-X-ENDLIST. The segment target is the longest segment the server promises. Players start about three targets from the live edge, so with 6-second segments a viewer sits roughly 18 seconds behind, before any encoder delay.

Why a stream that works elsewhere fails in a browser

• CORS. A browser only lets a page read a file from another site if that server sends Access-Control-Allow-Origin. Desktop players such as VLC and ffplay do not check it, which is why they play a stream this page cannot.
• Mixed content. An HTTPS page may not load an http:// stream. Serve the playlist and the segments over HTTPS.
• Expired or locked URLs. Signed URLs carry a token that expires, and some CDNs check the Referer. A 403 here usually means one of the two.
• Codecs. H.264 video with AAC audio plays in every current browser. HEVC, AV1 and some audio codecs depend on the browser and the device.

Streaming platforms work the other way round: your encoder sends RTMP to YouTube, Twitch or Kick, and they turn it into HLS for viewers. Their watch pages are not .m3u8 links, and their internal playlists are signed and locked to their own players, so they will not play here.

Reading an M3U8 file

An .m3u8 is plain text: open it in a browser tab or a text editor. A master playlist names one media playlist per rendition, with the tags the player uses to choose between them:

#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720,CODECS="avc1.64001f,mp4a.40.2"
720p/index.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=6000000,RESOLUTION=1920x1080,CODECS="avc1.640028,mp4a.40.2"
1080p/index.m3u8

Making an HLS stream to test

If you need a stream of your own, FFmpeg writes one from any video file. This plays the file in real time and keeps a live window of six 4-second segments:

ffmpeg -re -i input.mp4 \
  -c:v libx264 -preset veryfast -b:v 3000k -g 60 -keyint_min 60 -sc_threshold 0 \
  -c:a aac -b:a 128k \
  -f hls -hls_time 4 -hls_list_size 6 -hls_flags delete_segments \
  stream.m3u8

For 30 fps input, -g 60 puts a keyframe every 2 seconds and -sc_threshold 0 stops extra keyframes at scene cuts, so each 4-second segment starts cleanly. Drop -re and use -hls_playlist_type vod to write an on-demand playlist instead. Serve the folder over HTTPS, and send the CORS header and the right content types, for example in nginx:

location /hls/ {
    add_header Access-Control-Allow-Origin * always;
    types {
        application/vnd.apple.mpegurl m3u8;
        video/mp2t ts;
    }
}

Without the header, browsers on other sites, this page included, refuse to read the stream, while VLC still plays it.