VAST file recommendations

When creating a VAST ad item, we recommend that you upload multiple copies of the ad creative using different file formats, resolutions, and aspect ratios. This ensures maximum compatibility with common VAST-compatible video and audio players.

To upload additional VAST files to your ad item in AdButler, use the button at the bottom of the ad item setup form.

Include additional files

The recommendations and requirements listed here are based on the IAB's Digital Video In-Stream Ad Format Guidelines.

Filename, format and resolution


Use only alphanumeric characters for the names of media files. We also recommend that you use camel case, include the resolution, and seperate details with an _. For example: FallFishingPromo_640x480.mp4.

Resolution and Aspect Ratios

For linear ads, the IAB highly recommends including low, medium and high quality options to allow video ads to be rendered even in low bandwidth environments.

Mezzanine (VAST 4)
16:9 Up to 360p
Typical: 640x360
854x480 (PAL) 1024x576 (ATSC)
1280x720 1920x1080
1280x720 1920x1080
4:3 Up to 480p Typical: 640x480 480p-576p
640x480 (PAL) 768x576 (ATSC)
Not applicable 1440x1080
Video Bitrate 500-700 kbps 700-1500 kbps 1500-2500 kbps (720p)
2500-3500 kbps (1080p)
50 Mbps (VBR)
15-30 Mbps (CBR)
Audio Bitrate 128-192 kbps for AAC-LC
64-128 kbps for HE-AACv1
128-192 kbps for AAC-LC
64-128 kbps for HE-AACv1
128-192 kbps for AAC-LC
64-128 kbps for HE-AACv1
192 kbps (AAC)

The mezzanine file is the raw version of the ad's video or audio asset and can be used in VAST 4 ad items. Publishers can use this file to dynamically create the best file for the given setting. If you intend to use your ad with an ad-stitching server, the IAB recommends that you include a mezzanine file along with the low, medium, and high quality files.

File types


  • MP4 (H.264) for progressive download
  • HLS (M3U8) or MPEG-DASH for adaptive bitrate streaming
  • MP4 or MOV for mezzanine.


  • MP3
  • AAC
  • MP4
  • MPEG
  • OGG
  • WAV
  • WebM

Video Length

Maximum: 60 seconds

Recommended: 6, 15, or 30 seconds

Frame Rate

Maximum: 30 FPS

File size

Maximum: 50MB

Recommended: Less than 3MB

Ensure that your video files are optimized for web playback to reduce latency and CDN usage.

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