Guidelines for Video Ads

  • Updated

Video content is popular for online advertising. However, visitors often consider video ads as a disruptive experience. This is especially true when a video distracts them from their goal (such as reading a news article). Therefore, there are some guidelines for video ads to not alienate visitors due to a bad ad experience.

In-stream and Outstream Guidelines

In-stream video ads involve ad placements within a video. Even though in-stream video ads are vulnerable to ad blockers, they remain popular. Outstream video has an advantage over in-stream video because it delivers video ads anywhere with no limits related to ad placements.

  • In-stream Video: Linear video ads (such as pre-roll, mid-roll, and post-roll) are among the most popular video ads delivered within video content. However, visitors consider long pre-roll ads that can't be skipped and all mid-roll ads among the most intrusive ad types. Therefore, all pre-roll video ads longer than 31 seconds must provide a way for visitors to skip the ad within the first 6 seconds of ad play.

  • Outstream Video: Originally, outstream video ads got visitors’ attention by launching an autoplay video with the sound on. However, visitors find such videos to be the most distracting ads and frustrating. The current guideline suggests that autoplay video ads can only be in silent mode with sound intentionally activated by the visitor.


Video Ad Serving Template (VAST) is a script for video players to run video ads in partnership ad servers. Adform supports the VAST 2.0, VAST 3.0, and VAST 4.2.

Video Player Ad Interface (VPAID) is also a script for video ads to interact with video players, but it allows rich media. With VPAID, because of rich media, advertisers can gather information about how visitors interact with their video ads. Adform supports VPAID 2.0 for any standard video banner.


Over the Top (OTT) videos include ads associated with Connected TV (CTV), including game consoles, streaming devices, and smart TVs, as well as the ads shown on other digital devices (desktop and mobile).

Video Guidelines

For video ads use the following guidelines:

File Types

.mp4, .mpg, .mov, .webm, .ogv, .mpeg, .m4v, .mkv

Max File Size

100 MB

Audio Format

Stereo MP3 or ACC preferred

Sampling Rate

48,000 Hz (standard) or 96,000 Hz (professional)

Video Codec

When using the MP4 video format: H.264 (recommended)

Optimize for Web viewing and generate progressive scan with no interlacing

Ad Formats

Aspect Ratio

Recommended Size

Minimum Size

16:9 (Recommended)

1920x1080 pixels

640x360 pixels


640x480 pixels

480x360 pixels


(Low 240P) 300 – 2000 kbps (1080P Full HD)


Recommended Full HD (1080P)

Companion Banners

File Types: .png, .jpeg (.jpg), .gif

Ad Sizes: 1024x768, 970x250, 320x480, 300x250, 300x600, 1x1 (and possible custom sizes depending on the placement)

Clock Number Guidelines for VAST

Adform supports the Clearcast registry, which ensures that all video ads submitted to UK broadcasters follow the requirements of UK Codes of Advertising. UK broadcasters (accessed through FreeWheel SSP) require advertisers to submit a Clearcast clock number with their VAST tags.

A Clearcast clock number is a unique alphanumeric number that identifies the video ad and its source, for example, an advertising agency. This number allows advertisers to access UK’s Channel 4 and Sky Media CTV placements available through FreeWheel programmatic guaranteed deals.

The clock number format is AAA/BBBB123/456, where:

  • The first three letters are the Agency Code. Clearcast assigns this part of the number to you after you register with their service.

  • The four letters and three numbers in the middle are for information that is relevant to you. Use the four letters to identify your client or product. Use the three numbers to identify the ad you submit, for example, "001" for the first ad, "002" for the second one, and so on. You can also use different numbering, as long as it contains three digits.

  • The three digits at the end are the duration of the video ad. For example, if you want to submit a 30 second ad, the number at the end must be "030".


The clock number must follow the provided format, including the slashes ( / ) separating the three parts of the clock number.

You must register in the Clearcast clearance systems to submit your video ad for approval and get your Clearcast clock number. To get approval for your video ad, follow the clearance process provided in Clearcast documentation.

To add a Clearcast clock number to a VAST tag, contact Adform support and provide your campaign ID, the clock number, and the tag ID of your video ad.

Services that allow access to TV-like content delivered over the internet, bypassing traditional terrestrial TV formats. OTT services can be accessed via CTV, as well as through apps on other devices with an internet connection, such as smartphones and tablets.

Addressable (TV or video), Connected TV

Any television with an internet connection (for example, a smart TV).

Addressable (TV or video), Connected TV, Over-the-top

Was this article helpful?

How we can make it better?

Thank you for your feedback!