M3U8 parser: inspect an HLS playlist

How an HLS stream is put together

HTTP Live Streaming (HLS) cuts a stream into short files, usually 2 to 10 seconds each, and describes them in plain-text playlists that end in .m3u8. A master playlist offers the same stream in several versions, called variants, from a small low-bitrate picture to full HD or 4K. The player measures your connection and switches between variants as it plays, which is why picture quality can change mid-programme. Each variant points to a media playlist that lists the segments in order with their durations.

On a live channel the media playlist is a sliding window: the player reloads it every few seconds, new segments appear at the end and old ones drop off the top. A recording or film ends with #EXT-X-ENDLIST and lists every segment from start to finish, so the parser can add up its total length.

Tags the parser reads

Reading codec strings

The CODECS attribute uses short codes. avc1.640028 is H.264: 64 is the High profile and 28 (hex for 40) is level 4.0, enough for 1080p. hvc1 and hev1 are H.265 (HEVC); .2. after them is the Main 10 profile, used for HDR. mp4a.40.2 is AAC-LC audio, mp4a.40.5 HE-AAC, and ec-3 Dolby Digital Plus. The parser writes each one out in plain words. Whether a TV can play a variant depends on its decoders: a box without HEVC support cannot play hvc1 variants, so the player falls back to an H.264 one if the stream offers it.

Problems it points out

• Segments longer than the target duration. Strict players stop or skip when a segment overruns #EXT-X-TARGETDURATION.
• Variants without CODECS. The player has to download a segment to find out what it is, and may pick a variant the TV cannot decode.
• Audio groups that do not exist. A variant that names an audio group no #EXT-X-MEDIA defines plays without sound on some players.
• Missing BANDWIDTH or TARGETDURATION. Both are required by the HLS specification.
• A VOD playlist without ENDLIST. The player keeps reloading it as if it were live.

A live media playlist with no #EXT-X-ENDLIST is normal, not an error: the parser notes it so you know the segment list is only the current window. Encrypted segments are reported by method only; the key address is never shown.

To turn the bitrates into an internet speed, see internet speed for IPTV. For channel lists rather than streams, use the M3U checker, and for an Xtream login, the Xtream to M3U converter (its m3u8 output asks the server for HLS).