Split screen from one video by API: split and hstack

Use split to make two copies of the clip and hstack to place them side by side. The graph split[a][b];[b]eq=saturation=0[c];[a][c]hstack shows the original on the left and a gray copy on the right, from one source, in one MP4.

Runway's changelog (Aug 18, 2026) lists Compositing Nodes for composing and blending video. Sume's video filter takes a single clip, so this is a self-comparison, not a two-asset composite. Details are in Video filter, read 2026-10-01.

What does the request look like?

Internal labels like [a] and [b] are allowed; stream specifiers like [0:v] are not, because the server wraps [0:v]…[vout] itself.

curl -X POST https://api.sume.com/v1/video-filter \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: hstack-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/clip.mp4",
    "filtergraph": "split[a][b];[b]eq=saturation=0[c];[a][c]hstack"
  }'

Can I stack two different clips?

Not here: the filter surface takes one video_url. Timeline compose is the other surface, but the docs describe it as one still plus one video on screen at once, with image_fit and video_fit controlling how each sits in the frame, so it is not a two-video split screen either. For before-and-after reveals built from two images, see before and after video.

Which stacking filters are allowed?

What are the limits?

Output width doubles with hstack, so check the resulting size for your destination. Source length is capped at 300 seconds.