Skip to content
feega docs

Video playback and RAM preview

Scrub a video clip, press Option+Return, watch the green line fill, then play from memory.

Frame-accurate decoding

Section titled “Frame-accurate decoding”

Video clips decode with the browser’s WebCodecs API. Scrubbing or playing asks for the exact frame at the playhead, not the nearest one a <video> element can seek to.

  • Decoded frames are kept in memory, up to 1 GB. Going back to a frame you already saw costs nothing.
  • Frames decode at the size the clip is drawn, not at the file’s size. A 4K clip in a 1080p frame is held at about 1080p.
  • Up to four videos keep a decoder open at once; the least recently used one is released.
  • The same decoder serves the canvas, the editor preview and the exports.

If the browser has no WebCodecs, or cannot decode a file’s codec, the clip falls back to a <video> element. Nothing is shown to you; playback is just less smooth.

RAM preview

Section titled “RAM preview”

RAM preview decodes every video frame of a range ahead of time, so playing that range does no decoding.

  1. Optionally set a work area with I and O. Without one, the whole frame is cached.
  2. Press ⌥↵ or click the memory-chip button in the timeline bar.
  3. A green line under the ruler grows over the frames that are ready. Play when it covers the range.

Notes:

  • A frame counts as ready only when every video in it is cached.
  • If the range does not fit in 1 GB, the oldest frames are dropped and the green line shrinks to what is kept. Use a shorter work area.
  • Frames without a video are always ready. The cache holds decoded video only; text, shapes and effects are still drawn live.
  • Starting another RAM preview stops the one in progress.

Measured

Section titled “Measured”

4K H.264 clip, 30 fps, drawn at 1920 px wide, Chrome on an Apple Silicon Mac:

<video> elementWebCodecs
Seek to a random time, median56 ms49 ms
Seek to a random time, 95th percentile97 ms94 ms
Seek to a frame already cachednot cached0 ms
Playing 5 s live, frames dropped of 1505756
Playing 5 s after RAM preview, frames droppednot available0

Decoding a 4K file live is limited by the decoder in both cases. RAM preview is what makes it play at full speed.