Creative transcoding, resizing, and letterboxing

Due to the many distinct screen resolutions and file formats in DOOH, Vistar uses a few methods to ensure creatives match the required resolutions and formats across all media owner networks. These methods include transcoding, resizing, and letterboxing. Vistar factors in these adjustments when providing media buyers guidance on creative specifications to help them plan their campaigns and upload the correct size of creatives.


Transcoding is the process of converting a video file from one format to another format. Vistar uses a third-party service, Zencoder, to transcode all uploaded creative assets to the ad platform to match the required formats across its different media owner networks. You can view a list of available input and output formats that Zencoder can handle. For technical details on the transcoding outputs, see here.

Our system automatically convert all .png creatives to .jpg by default to reduce the chances of campaigns being blocked due to incompatible file type.

Any video creative you upload on the direct side or a buyer uploads in their DSP is transcoded, provided the creative resolution is no greater than 3840x2160 and vice versa.

Note: When a request is sent for both static and video MIME Types and a static file is transcoded, the ad server returns an ad response with the following logic: 

  1. The system chooses a static image asset first.
  2. The system selects the asset with the highest bitrate if there is no image.
  3. If the bitrates are identical, the system alphabetically chooses based on asset URL.



Vistar uses resizing to allow a larger resolution creative to deliver on smaller resolution screens in an effort to exactly match the media owner’s requested resolution. Through resizing, Vistar generates new image or video files with a smaller resolution than the image or video that a buyer uploaded while keeping aspect ratio constant, exactly matching the resolution of the targeted inventory. You can review resized assets in the creative approval view by clicking on the number in the Assets column.

In addition to resizing on Vistar’s end, Vistar will also return a creative that’s aspect is within 6% of the requested aspect ratio and allow the media owner to display the creative.

Vistar also now checks for the exact display area and the mapped resolution of a venue when matching new creatives. This means that creatives built to match non-standard display areas can now be submitted and matched to a venue for media owner approval. 


Letterboxing is the process of adding black bars to the top and bottom or left and right of an image or video so that the image or video can be shown with a slightly different aspect ratio. When letterboxed the original image or video is not cropped, stretched, flattened, or modified in any way, as shown in the following example:

Original Asset:


Letterboxed Asset:


Vistar uses letterboxing to allow buyers to upload standard sized creatives and have them be eligible to deliver on non-standard screen sizes. This increases the reach of standard sized creatives, so media owners can more easily monetize screens with non-standard sizes and buyers are not responsible for uploading creatives for every single distinct size to deliver across all targeted inventory. Like with resizing, you can review letterboxed assets in the creatives approval view by clicking on the number in the Assets column. Letterboxed assets are indicated by a check-mark in the Letterbox column. 

Note: Letterboxing is disabled for media owners by default. To opt into letterboxing, please reach out to

Vistar’s letterboxing process will enable standard sizes to be eligible to serve on screens with aspect ratios within 25% of that standard size. The upper and lower bounds of this process are outlined in the table below:




Aspect Ratio

Lower Bounds

Upper Bounds



























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