Substack video is email-first; 16:9 may be right

Do not force 9:16 if the player is landscape. Substack video that lives in the issue is email-first: a reader opens a message or a post on a wide pane. A vertical clip dropped into that pane is letterboxed, cropped, or both. The default that makes sense for Reels is not the default for the inbox.

Newsletter writers on Versely already split two jobs: a talking-to-camera insight clip and a screen-recording scroll through a recent issue for social, versus the writing itself in the inbox. The audience page lists 9:16 because the promo surface it names is X and Threads. That is not a ruling on the player inside the email.

Email is a landscape player

The issue is read on a laptop, a tablet, a phone held however the reader holds mail. The video you embed in that issue sits in a wide slot. 16:9 fills it. 9:16 wastes it.

Change a video's aspect ratio is the general reframe: edit_video takes the clip and an aspect_ratio, including 16:9 for widescreen. Preview is a free 480p render (preview:true, per-user cooldown) before the charged export. Reframing does not invent picture. A 9:16 talking head forced to 16:9 will crop or pillarbox; if the insight clip was shot vertical, keep it for social and make a different file for the issue.

If you already have a vertical promo, convert vertical video to horizontal is the named path the other way. Use it when the master is 9:16 and the email needs 16:9 — and only after you have decided the email is the destination.

A screen-recording of the issue is landscape by nature. Do not crop the archive view into a phone frame to look like a Reel. The archive is the product.

Vertical is a second placement

9:16 still earns its keep. It is the format for the clip that proves the writing in fifteen seconds on X or Threads: one insight, to camera or over a tight crop, posted three times a week on that audience's cadence. That file is a promo. It is not the issue.

Shoot or generate the insight clip at 9:16 if that is where it will play full-screen. Shoot or cut the in-issue file at 16:9 if that is where it will play. One master stretched into both is how a face sits under chrome in one place and in a postage stamp in the other.

Do not run a week of 9:16 exports because "short-form is vertical." Short-form on a phone app is vertical. Short-form inside an email is whatever the player is. Honesty about the player is the whole decision.

Ask your own numbers before you crop

Pick the right format for each platform is the decision step, not the reframe. get_content_insights reads your recent posts through Versely's social integration and breaks them down by platform and format — image, video, carousel, text — with counts, average and median views and engagement, and the top three posts. Best posting hour and day come back only when the timestamps allow it.

It is not a generic "always 9:16." It is not a Substack dashboard. It will not tell you how the inbox player behaves. It will tell you whether your connected accounts already prove video, carousel, or text, so you do not spend an afternoon converting a back catalogue toward a shape those accounts have never rewarded.

A brand-new account with nothing posted has nothing to summarize. Insights recommend. edit_video reframes. Preview at 480p, then pay for the export.

If the destination is the issue, you do not need insights to pick 16:9. You need the player. If the destination is the promo, run insights on the social accounts, then reframe toward whatever those accounts already prove.

Two files. Two ratios. One bill for the export you actually ship.

FAQ

Should every newsletter video be 16:9?

No. The file that sits in the issue should match the player, which is usually landscape. The file that sits on X or Threads can stay 9:16. Do not merge them to save an export.

Will pick-the-right-format tell me to use 16:9 on Substack?

No. It reads posts on connected social accounts, not the email player. Use it to decide the promo shape. Use the player to decide the issue shape.

Can I preview a 16:9 reframe without spending credits?

Yes. edit_video with preview:true returns a free 480p render, with a per-user cooldown. The final export is the charged job.

I only have a vertical talking-head. Should I letterbox it in the issue?

Better to keep that file on social and cut a landscape version for the email — a screen-scroll of the issue, a wide desk, a 16:9 insight take. Letterboxing a 9:16 clip in a wide player is the thing this page is for avoiding.