broadcast-hls

HLS (M3U8) playlist syntax, RFC 8216 and RFC 8216bis (Low-Latency HLS): typed Media and Multivariant (Master) Playlist parse and serialize, no_std.

[dependencies]
broadcast-hls = "0.4"

What it does / what it does not

Does: parse a playlist into MediaPlaylist or MasterPlaylist structs and render it back with to_m3u8(), covering every one of the 32 tags in RFC 8216bis §4.4 (28 as typed struct fields, 4 preserved verbatim), the Low-Latency additions (partial segments, blocking reload, delta updates, preload hints, rendition reports), I-frame trick-play, discontinuity signalling, and the EXT-X-KEY line for CENC/CBCS protected CMAF. EXT-X-VERSION is computed from the content, never trusted from a caller. It was extracted from transmux (issue #878) so a crate that only needs playlist syntax (media-doctor, an HLS-pull client, a fuzz target) does not pull in a container-muxing hub.

Does not: fetch anything or run a client (that is hls-runtime), produce segments (transmux's ts_hls and ll_hls segmenters stay there because they emit container bytes), validate cross-file semantic rules (media-doctor), or give typed access to EXT-X-KEY, EXT-X-PROGRAM-DATE-TIME, EXT-X-DATERANGE and EXT-X-MEDIA (they round-trip losslessly as tag lines, but you cannot read or build them through a field). HLS Interstitials (CLASS="com.apple.hls.interstitial" date ranges) are therefore built by the caller (ssai-runtime renders them) as EXT-X-DATERANGE lines, and the interstitial spec (docs/interstitials.md) is transcribed but not typed here.

Standards supported

Features

Quick start

Parse a real Apple BipBop media playlist (a committed fixture) and render it back:

use broadcast_hls::MediaPlaylist;

let text = std::fs::read_to_string("../fixtures/hls/real/bipbop-ts/gear1-video.m3u8").unwrap();
let playlist = MediaPlaylist::parse(&text).unwrap();
assert!(!playlist.segments.is_empty());

// to_m3u8 is the symmetric inverse of parse: a second parse equals the first.
let rendered = playlist.to_m3u8().unwrap();
assert_eq!(MediaPlaylist::parse(&rendered).unwrap(), playlist);

Build a playlist from fields (DecimalSeconds rejects NaN and infinity, to_m3u8 is fallible):

use broadcast_hls::{DecimalSeconds, MediaPlaylist, MediaSegment};

let playlist = MediaPlaylist {
    target_duration: 10,
    segments: vec![MediaSegment {
        uri: "seg0.m4s".into(),
        duration: DecimalSeconds::new(9.009).unwrap(),
        ..Default::default()
    }],
    endlist: true,
    ..Default::default()
};
let m3u8 = playlist.to_m3u8().unwrap();
assert!(m3u8.starts_with("#EXTM3U"));
// The renderer computed `#EXT-X-VERSION` from the content; parsing reads it back.
let reparsed = MediaPlaylist::parse(&m3u8).unwrap();
assert_eq!(reparsed.segments, playlist.segments);
assert_eq!(reparsed.to_m3u8().unwrap(), m3u8);

Runnable programs: cargo run -p broadcast-hls --example build_playlist and --example parse_playlist.

What is implemented

• MediaPlaylist and MediaSegment: segments with title, map (carry-forward on parse, deduplicated on render), bitrate, gap, discontinuous, byte ranges, and pre_tags (segment-defining tags kept in place), plus playlist-level extra_tags for unrecognised tags.
• MasterPlaylist, Variant, IFrameVariant: multivariant playlists with EXT-X-I-FRAME-STREAM-INF trick-play (RFC 8216 §4.3.4.2) and MasterPlaylist::extra_tags.
• The 28 typed tags: including EXT-X-INDEPENDENT-SEGMENTS, EXT-X-START (StartPoint), EXT-X-DEFINE (Define), EXT-X-PLAYLIST-TYPE (PlaylistType), EXT-X-GAP, EXT-X-BITRATE, EXT-X-SESSION-DATA (SessionData), EXT-X-SESSION-KEY (SessionKey, EncryptionMethod) and EXT-X-CONTENT-STEERING (ContentSteering). tests/hls_tag_completeness.rs parses a fixture carrying all 32 and asserts typed tags populate their field and the four opaque ones survive verbatim.
• Low-Latency HLS (opt-in, so a plain playlist is unchanged): LowLatencyConfig, PartSpec, OpenSegment (the in-progress segment at the live edge), MapTag, ByteRange, PreloadHintType, RenditionReport, SkipInfo. PART-HOLD-BACK must be at least three part targets.
• Discontinuities: EXT-X-DISCONTINUITY and EXT-X-DISCONTINUITY-SEQUENCE, and mark_init_discontinuities (detect an init-segment change across a run).
• Version derivation: MediaPlaylist::computed_version and MasterPlaylist::computed_version apply the draft's §8 table (docs/version-compatibility.md). A playlist needing nothing gets no EXT-X-VERSION tag. The version field is a floor: raised to the computed value, never lowered.
• Attribute lists: parse_attribute_list, render_attribute_list, AttrValue (validated quoted or bare value), and unknown attributes on every modelled tag kept in extra_attrs and re-emitted after the known ones.
• Durations: DecimalSeconds and SignedDecimalSeconds round-trip bit-exactly (including 9.9766 and 2.00004). Round your own durations before building if you want compact playlists, since an unrounded division renders every digit.
• CENC: cenc_ext_x_key, CENC_KEYFORMAT, CENC_KEYFORMATVERSIONS.

Round-trip fidelity

The workspace text-format rule is that a second parse of the rendered output equals the first parse, not that the text is byte-identical. What changes on re-emit:

• Tag order is canonical, not input order (for example INDEPENDENT-SEGMENTS, DEFINE, START follow the version line; SESSION-KEY, SESSION-DATA, CONTENT-STEERING precede the variants). No tag is lost.
• Blank lines, trailing whitespace and # comment lines are dropped. Line-continuation backslashes (used for wrapping in spec examples) are never emitted.
• to_m3u8() is fallible: a quoted-string or URI field containing ", CR or LF (Error::InvalidQuotedString, Error::InvalidUri) is rejected instead of rendered, which prevents tag-line injection. The same applies to an EXT-X-SKIP removed-daterange id.
• Not enforced: EXT-X-BITRATE not applying to a byte-ranged segment, EXT-X-DEFINE IMPORT and QUERYPARAM resolution, EXT-X-SESSION-KEY METHOD not being NONE, "must not appear more than once" rules. Those need cross-file context and belong to media-doctor.
• A non-segment-defining unrecognised tag lands in extra_tags and loses its interleaved position (it renders as one block before the segments). Segment-defining tags (EXT-X-KEY, EXT-X-PROGRAM-DATE-TIME, EXT-X-DATERANGE, EXT-X-CUE-*) attach to the following segment's pre_tags and keep their place.
• A hand-built playlist whose segments' map fields do not form a valid carry-forward sequence cannot round-trip, because the wire has no "stop applying the map" short of a discontinuity plus a new map.

Design notes

Zero dependencies beyond broadcast-common and thiserror, no_std + alloc, symmetric parse and render, #[non_exhaustive] on Error and the open enums, label-coverage tests for spec enums, fixture corpus (tests/hls_fixture_corpus.rs) over Apple's BipBop playlists and every RFC 8216bis §9 example (provenance in fixtures/hls/MANIFEST.md), and a fuzz target.

Related crates

Depends on broadcast-common. Consumed by hls-runtime (client parses, origin renders), transmux (the HLS segmenters), ssai-runtime (interstitial playlists), media-doctor (conformance checks), timed-metadata (daterange lines) and multimux.

MSRV and licence

MSRV 1.95.0. Licensed under MIT OR Apache-2.0.