Open and close a clip with a white flash: the fade filter

To open a clip with a white flash and close on white, send Sume's video filter two fade filters: fade=t=in:st=0:d=0.4:color=white,fade=t=out:st=2.6:d=0.4:color=white. The first brightens in from white over 0.4 seconds; the second leaves to white starting at 2.6 seconds, so it fits a 3 second clip. The change affects the picture only, costs $0.02 and has a free check.

Sume's Timeline has its own edge fades, output.fade_in_seconds and output.fade_out_seconds up to 5 seconds each, and those are described as seconds only, with no colour field. When you want white, or want the fade on one clip before assembly, the filter is the route.

How do I get the out time right?

The out fade needs a start time, st, equal to the clip duration minus the fade length. Read the duration from the video inspect probe (a probe-only call with frames:false returns it) or from the duration_seconds of the job that made the clip. For a 7.5 second clip with a 0.5 second fade, st is 7.0.

If st is later than the clip's end, the out fade never starts, and nothing tells you. Check one still near the end with video frames after the job.

What happens to the sound?

The filter graph touches video only. Sume's video filter keeps the source audio unless the program changes it, so the sound does not fade with the picture. If you want sound to dip as well, build the edit in Timeline, where the spine and its fades are handled together, or fade the audio separately.

A clip with no audio track raises a soft warning, filter_source_has_no_audio, and still encodes.

curl -X POST https://api.sume.com/v1/video-filter/check \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/clip.mp4",
    "filtergraph": "fade=t=in:st=0:d=0.4:color=white,fade=t=out:st=2.6:d=0.4:color=white"
  }'

Which variants are common?

color takes a colour name or hex. Keep to simple names, because the validator refuses quotes and backslashes.

Should I fade before or after assembly?

Fade a clip before assembly only if the flash is part of that shot. For an overall fade on a finished video, use the Timeline edge fades so the picture and the voice spine stay together. A white fade placed on a clip and then joined with a Timeline transition can pile effects on each other, so keep the join a hard cut.