Reddit Video Ads: Video Sizes, File Limits and Thumbnail Specs

A Reddit video ad is built from three parts: a headline, a video, and a link to your site.

A video file has more requirements than an image, and not all of them are obvious. MOV is on the list of accepted formats, but the ProRes codec is not supported. The size limit is 1 GB and the frame rate limit is 30 FPS. Length runs from 2 seconds to 15 minutes, with a recommendation of 5 to 30 seconds. Aspect ratios depend on the devices you plan to run on.

Below are the requirements for every element of a video ad: headline, links and button, file, length, sizes by device, and thumbnail. Plus how the format is displayed in the feed, in comments, and in the app, because that decides whether a person sees a video or a still frame. All numbers come from the Reddit Ads help center.

How a Video Ad Is Displayed

A Reddit ad runs in two places: the feed and the comments under a post. Reddit recommends turning on both placements so the ad picks up every impression available. Comments under the ad itself are turned on with a separate toggle in the setup.

The feed also has a view mode. In card view the post takes the full width and shows the media in full. In compact view it collapses into a headline row with a small image next to it.

Then comes the part that makes the video format harder than it looks. The help center describes video behavior in four rules, and they depend not only on where the ad shows, but on the environment: app or browser.

• Feed on desktop and mobile: the video autoplays. Redditors can turn autoplay off in their account settings.
• Conversation and feed on desktop and mobile web: the video plays on click.
• Compact view on desktop and mobile web: the click takes the person to the landing page, the video does not play.
• All placements in the app: a page opens where the video plays alongside the landing page.

The first two rules overlap: the desktop feed falls under autoplay and under play on click at the same time. The help center does not say which rule wins.

Here is what follows for certain. A click and a view are not the same event. In compact view there is a click but no view: the person leaves for the site without seeing a second of the video. In the app it works the other way around, the view happens alongside the landing page.

Headline

The headline is required and holds up to 300 characters. Reddit recommends staying within 100 characters, or within 80 if truncation is a concern.

The help center names the reasons for truncation: browser, device, and font display size. All three sit on the reader's side, so the cutoff point cannot be calculated in advance. The same headline breaks in different places for different people.

That is where the 80 character recommendation gets its practical meaning. It is not a style note. It is the only way to make sure the headline is read in full no matter which screen it shows up on.

Links and Button

The destination URL is required and holds up to 268 characters. The display URL holds up to 100 characters, and its domain has to match the domain of the destination URL. The button is picked from a list of preset options in the ad setup.

268 characters look like plenty until tracking is added to the link. Here is an address with five UTM parameters:

https://example.com/summer-collection?utm_source=reddit&utm_medium=cpc&utm_campaign=summer_sale_2026_video_us&utm_content=video_16x9_v3&utm_term=r_technology

That is 157 characters, and 120 of them are the tracking tail. The address itself takes 37. What is left is 111 characters of headroom, and it runs out with a long campaign name or an extra ID from a partner system.

The domain requirement on the display URL rules out one trick: you cannot put someone else's address there. Not a redirect domain, not a partner domain, not a shortened link.

Video File

Reddit accepts MP4 and MOV. The ProRes codec is not supported. The size limit is 1 GB and the frame rate limit is 30 FPS.

The note about ProRes matters more than it looks. MOV is a container, not a codec: the same .mov file can hold ProRes or H.264. So the extension says nothing about whether the file will pass. What you check is the codec, in the export settings or in the properties of the finished file.

30 FPS is a limit, not a recommendation. A 60 frame timeline has to be re-exported.

Any aspect ratio is accepted. Ratios outside the recommendations produce letterboxing, meaning bars along the edges of the frame. The recommended ratios are covered below, in the section on sizes.

Length

A video has to run at least 2 seconds and no longer than 15 minutes. Reddit recommends 5 to 30 seconds.

The gap between the limit and the recommendation is the widest one in the whole spec. 15 minutes is 900 seconds, thirty times the upper end of the recommendation. Compare that to the headline: a 300 character limit against a 100 character recommendation, a difference of three times.

Read it this way. 15 minutes describes what the platform will accept. 5 to 30 seconds is the working range.

The lower bound matters too. A video shorter than 2 seconds cannot be uploaded, so a one second bumper does not work on Reddit.

Sizes by Device

The help center splits the recommendations into three sets: one video for all devices, mobile, and desktop. Within each set Reddit advises using the highest resolution that meets the ratio you need.

One video for all devices. Landscape 4:3 (1440 × 1080 px) or Landscape 16:9 (1920 × 1080 px).

Mobile. Recommended ratios:

• Square 1:1 — 1200 × 1200 px
• Portrait 3:4 — 900 × 1200 px
• Portrait 4:5 — 1200 × 1500 px
• Landscape 4:3 — 1440 × 1080 px
• Landscape 16:9 — 1920 × 1080 px

Desktop. Recommended ratios are Landscape 4:3 (1440 × 1080 px) and Landscape 16:9 (1920 × 1080 px) — the same pair as the cross-device recommendation.

Acceptable ratios — meaning they will run but may cause formatting discrepancies — are Square 1:1 (1200 × 1200 px) and Portrait 3:4 (900 × 1200 px).

One pattern comes out of the three sets. Neither the all devices set nor the desktop set includes a vertical ratio or a square. Only 4:3 and 16:9. Square and vertical are recommended for mobile only.

That leaves a choice between two options. One landscape video for every surface, the way the help center suggests. Or two files, vertical for mobile and landscape for desktop.

1:1 and 3:4 show up in the help center twice: in the mobile recommendations and in the list of acceptable ratios with the note about formatting.

Thumbnail

The thumbnail is the frame shown before the video plays. Reddit generates it automatically from the uploaded video. You can upload your own image instead, then crop it and adjust its size right in the ad setup.

JPG, PNG, and GIF are accepted, with a 3 MB size limit. The help center does not name a resolution. The one requirement is that the thumbnail ratio matches the video ratio.

Here is a conclusion the help center does not draw. The thumbnail is not a technical field you can leave alone. Part of the audience sees it instead of the video. Autoplay can be turned off in account settings, and then a still frame is all that stays in the feed. In compact view the video does not play at all.

So the first frame of the video has to work as a picture on its own. If the automatic thumbnail landed on a blurred frame or on a cut between scenes, replace it with an upload.

Pre-launch Checklist

Half of the requirements are visible in the file itself. The other half only show up in the interface after upload.

In the file, before upload:

• the codec, not the extension: MOV works as long as ProRes is not inside;
• file size no larger than 1 GB;
• frame rate no higher than 30 FPS;
• length no shorter than 2 seconds, working range 5 to 30 seconds;
• aspect ratio matched to the placement plan: one landscape video for all devices, or two files, vertical for mobile and landscape for desktop.

In the interface, after upload:

• which frame Reddit picked for the automatic thumbnail;
• headline length: 300 character limit, 80 if truncation is a concern;
• the display URL domain matches the destination domain.

No screen will show you the truncation point of a headline. It depends on the browser, the device, and the reader's font settings, and all of that sits on their side. So 80 characters is not a pre-launch check. It is a decision you make while writing the headline.