Delivery primer: letterboxing 21:9 inside 16:9
A 21:9 picture delivered for 16:9 screens is letterboxed: black bars above and below, the full wide frame in the middle. Two vendors on the sheet generate 21:9 directly. From 2 source pages, read 2026-09-25 to 2026-10-25; no maker pays to be listed.
A 21:9 picture delivered for 16:9 screens is letterboxed: black bars above and below, the full wide frame in the middle. Two vendors on the sheet generate 21:9 directly.
The alternative is to generate 16:9 and crop to 21:9 in the edit, which loses the top and bottom of every shot and needs framing planned for it.
Either way, the delivered file stays 16:9; only the active picture changes shape.
Check the platform first: some accept a native 21:9 file and add their own bars, others ask for the bars to be in the picture.
1Vendor figures that bear on it
Aspect ratio of the generated video. Valid values: adaptive (Default value)
Alibaba Cloud Model Studio, Wan3.0 video generation API reference
16:9 / 9:16 / 4:3 / 3:4 / 1:1 / 2:3 / 3:2 / 21:9
PixVerse platform docs, model capability map
- Wan3.0 video generationAdaptive by default; fixed shapes run from 21:9 cinema width through 16:9, 4:3 and square 1:1 to 3:4 and 9:16 portraitratio parameter
- V6Eight shapes on V6, from 21:9 cinema width through 16:9, 3:2, 4:3 and square 1:1 to 3:4, 2:3 and 9:16 portraitaspect ratios row
2How one pipeline outputs it
For a delivery question like “Letterboxing 21:9 inside 16:9”, SceneMixer states the following about what it produces:
Every episode is scored for you once its first shot is generated; the music is written for the episode and mixed in under the voices.
SceneMixer, Background Music in an AI Short Drama: The Built-in Score — “Do I need to add music to my episode?” (read 2026-10-13)
Lip sync is the default: the picture stays frame for frame, every line is voiced again and the mouths are moved to match; the original ambience is dropped.
SceneMixer, Lip Sync or Re-perform: Choosing How to Redub a Clip (read 2026-10-13)
3Continue the primer
The primer reads printed figures; it does not measure any vendor's files.