Generate HLS I-frame (trick-play) playlists with ffmpeg for fast-forward and rewind
domain: ffmpeg · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Encode the source with a strict closed-GOP structure so every segment starts with an IDR frame; use -force_key_frames 'expr:gte(t,n_forced*SEG_DURATION)' to enforce keyframe placement
Pass the -hls_flags iframes_only flag to the ffmpeg HLS muxer to produce an I-frame-only playlist that uses EXT-X-BYTERANGE to reference individual I-frames within segments
In the multivariant playlist, add an EXT-X-I-FRAME-STREAM-INF tag for each I-frame playlist, specifying BANDWIDTH, CODECS, RESOLUTION, and URI
Set EXT-X-VERSION to at least 4 in the I-frame playlist as required by the spec
Test trick-play behavior in AVPlayer on iOS (which uses I-frame playlists natively for scrubbing) and verify that fast-forward speeds display correct frames
Known gotchas
I-frame playlists generated by ffmpeg use EXT-X-BYTERANGE mode, which requires the HTTP server to support range requests; if the CDN strips Range headers, trick-play requests will return full segments
The BANDWIDTH declared in EXT-X-I-FRAME-STREAM-INF should reflect I-frame-only bitrate (much lower than full video); over-declaring it causes ABR players to de-prioritize the track
Shaka Packager and Bento4 can generate I-frame playlists more reliably than ffmpeg for complex sources; prefer those tools for production pipelines where keyframe precision is critical
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