Direct

Play a video release in the browser without re-encoding it.

A browser that can decode the release's video itself — H.264 everywhere, HEVC on anything Apple makes and on desktops with a hardware decoder, AV1 on most — only needs the container changed and the audio put into AAC. So ffmpeg copies the video into one fragmented MP4 that grows while it plays, and the HLS playlist names byte ranges of that file. A fraction of a core instead of the several a re-encode takes; and it is the only form of HEVC Safari plays through HLS at all.

def deps do
  [{:direct, "~> 0.1"}]
end

Needs ffmpeg and ffprobe on the path. Built on fmp4.

Setting up

# application.ex
children = [Direct.Supervisor, …]

# config
config :direct, root: "/var/cache/video"   # or dir: fn id -> path end

Starting a play

The page tells the server what its browser decodes when it connects:

const v = document.createElement("video")
socketParams = {
  hevc: v.canPlayType('video/mp4; codecs="hvc1.1.6.L120.B0"') !== "",
  av1: MediaSource.isTypeSupported('video/mp4; codecs="av01.0.08M.08"'),
}

caps = Direct.Caps.from_params(connect_params)

case Direct.start(url, name: filename, size: filesize, caps: caps, from: resume_seconds) do
  {:ok, id, part} -> # play /stream/#{id}/playlist.m3u8#{Direct.part_query(part)}
  :skip            -> # this browser cannot decode the video: re-encode, or offer an external player
  {:error, :unreachable} -> # the file could not be probed
end

start/2 probes the file once (streams.json), and joins a conversion already running or finished for the same id.

Serving

Everything is files under Direct.dir(id):

# playlist.m3u8 — a media playlist, or a master when there are several audio tracks
Direct.playlist(id, part, prefer: ["ja", "en"], subs: subtitle_tracks)

# video.m3u8, audio0.m3u8 … — the media playlists of a master, byte ranges of what is written
Direct.media_playlist(id, part, "media")
Direct.media_playlist(id, part, "audio0")

# media.mp4, audio0.mp4 … — the files, with Range support for a growing file
Fmp4.RangeFile.send(conn, Direct.file(id, name), "video/mp4")

Call Direct.touch(id) on each fetch: a conversion nobody has fetched for ten minutes (config :direct, idle_ms:) stops, and what it wrote stays as a cache for you to sweep. Direct.running/0 lists the ids converting.

Parts

Coming back to a film half-way through should not mean converting the half already seen. from: starts a conversion at that second (a part, media-1800.mp4), keeping the film's own clock: its fragments carry the real times, so subtitles for the whole film still fit and the player can show the real position. Direct.start_at(id, part) says where it begins (ffmpeg lands on the keyframe before); Direct.parts(id) lists the parts on disk. A finished part that covers the place asked for is reused. Parts within min_part seconds (default 60) of the start are not worth it.

Several audio tracks

A release with one audio track becomes one media.mp4. With several, the video goes alone into media.mp4 and each track into audioN.mp4, listed in audio.json with a name ("Japanese", "Russian 2"), and playlist/3 returns a master with one rendition per track — the first in the preferred language the default. Direct.Playlist.tidy_master/2 does the same for ffmpeg's own HLS master of a TS conversion.

Subtitles

Text subtitles inside the release are written out as subN.vtt while the conversion runs (subs.json lists them; image subtitles are left out). Serving them as HLS subtitle renditions — cut to the stream's segments — is yours to do; pass what you serve as subs: and they are listed in the master.

License

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