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Ad Validation Made Easy

VAST Tag Tester

Check Audio Loudness, Video Codecs, Dimensions, MOOV Atoms and much more!

Ad Tag
Ad Spec
Go ahead, try
it yourself !

Dylan Coetzee
Digital Marketing Director, OmniaMed Communications

VAST Video Inspector Validator

Ad System

The name of the ad server who serves the VAST tag. It's not actually important, but it's just nice to know with who you're dealing with. Some publishers have a restricted list of ad server technology partners with whom they are doing business with.

CORS Header

The cross-origin resource sharing (CORS) header tells the browser if the document can be loaded from a different domain than on which it is hosted. Without a proper CORS header, the browser won't be able to load the XML document. In that case, the video ads won't load and is considered a big configuration mistake.

Creative Count

The number of creatives found in the XML document. If no creatives are returned, the ad server either targets the campaign to a subset of users, or the campaign is no longer active. Note that the creative count does not reflect the number of media files. A creative can have multiple media files for the player to choose from.


Determines if the URL was loaded over http or https. Non-secure http:// pages are almost gone these days. It's imperative your VAST URL loads over a secure TLS connection (https). If not, browsers will refuse to download the XML document and consequently no ad will be played.

VAST Version

The version of the VAST tag that is being served. The video player on the publisher's side may only be capable of handling certain versions of the VAST specification. This test allows you to double-check if the correct version has been chosen.

Wrapper Redirects

Determines if the VAST tag is wrapped in another VAST tag, and how many times. Multiple parties may want to track metrics of the campaign (publishers, networks, agencies). By wrapping tags, each can add their own measurement pixels. Wrappers however increase latency and should be kept at a minimum.

XML Content-Type

The mime-type of the document on the VAST URL. It's good practice to set the correct content-type header, depending on the type of content the server sends back. In case of XML, the content-type should be text/xml.

XML Load Time

The time it took to download the XML document. Servers that are under load or mis-configured may send the XML file in multiple parts, which results in additional download time. The faster the XML document is loaded, the faster the video can play.


The HTTP status code when fetching the VAST URL. A status 200 means everything's fine. This tells the video player if the XML document was received correctly. That doesn't necessarily mean a video ad is available — think about geotargeting or frequency capping. Campaigns that are no longer active may return a 404.

XML File Size

The total size of the XML file that was downloaded, in bytes. Users on slow networks may have to wait some time before the XML file has been downloaded. During that time, no video can be played. This has a negative impact on user-experience.

Impression Logging

Wether or not the VAST document has impression logging enabled. Impression logging is imperative in order to track how many VAST ads are served. Note that this doesn't necessarily mean the video has been played, as this is measured using the 'start' event tracker.

Audio Channels

The number of channels on which audio information is stored. Usually 2 (stereo). Videos with more than 2 audio channels are commonly meant for (home) cinemas. For video ads, it may just be too much.

Audio Compression

The audio compression method refers to the amount of deleted audio information during encoding. It's either lossy or lossless. Lossless algorithms preserve the original audio data so the sound is exactly the same after compression. Lossy algorithms remove parts of the audio information, but encodes it in a way we barely hear a difference. Lossy compression is preferred as it results in less file size with a negligible loss in quality.

Audio Sample Rate

The audio sample rate defines how many times per second a sound information is stored. Common samples rates at 44.1 and 48 kHz. A sample rate that is too low results in poor audio quality. Higher samples rates result in better quality, but also comes with a higher file size.

Audio Codec

The audio codec is the algorithm used to encode the audio stream. Today's standard is AAC. In order to play, the browser or device must support the codec to decode the video. AAC (Advanced Audio Coding) or AAC-LC (low complexity) are supported by almost all browsers and devices. If you're serving the video with a different codec, make sure your targeted device supports it.

Audio Loudness

The audio loudness refers to the perception of sound. It's measured in LUFS or LKFS, where -24 is a commonly accepted value. The audio loudness can be set high or low while creating the video. If the video ad is much louder than the original video content that was being played before the ad, this may not be appreciated by the user. YouTube, NetFlix and Apple Music all have maximum LUFS levels to maintain a good user-experience.

Audio True Peak

The true peak refers to the maximum loudness peak throughout the video. A common threshold is < -1 dB. Imagine a video of nature: a river with some butterflies — just some soft meditation sounds. Then there's an explosion. LUFS levels are determined by averaging the video's loudness over time. It may have been in an acceptable range in this example. The true peak however detects the explosion, as it was the loudest part of the video.

Audio Bit Rate

Defines the amount of data stored for every second of audio. Common bit rates are 128, 256 or 320 kbps. Higher bit rates result in better sound quality, as more audio data can be stored per second. It's however a trade-off between file size and quality.

Video Aspect Ratio

The aspect ratio is the video width in proportion to the height. A common aspect ratio is 16:9. On the web page of app where the video will be played, the ad unit will likely expect a video that matches the placeholder's aspect ratio. You want to avoid playing portrait videos in a landscape container, as it may be considered a bad user-experience.

Video Dimensions

The width and height of the video, in pixels. Common sizes are 1920x1080, 1280x720 and 640x360. Serving a video in a non-standard size may lead to letterboxing by the video player: black bars usually at the top and bottom of the video. While technically the video will play fine, it may not be a great user-experience.

Video Duration

The duration of the video in seconds. Common ad durations are 10, 15 or 30 seconds. Publishers commonly have restrictions regarding the duration of videos. Videos taking too long may abandon users. Too short and it may be difficult to transmit the message.

Video Bit Rate

The container bit rate defines the amount of data stored for every second of audio + video. Higher bit rates result in better video/audio quality, as more data can be stored per second. It's however a trade-off between file size and quality.

Video Bit Rate Mode

The bit rate mode determines wether or not the amount of data stored per second remains constant over time. Contant bit rates means that the amount of data your device has to load every second remains the same. It's therefore more reliable on slow networks. Variable bit rates result in higher quality, but the data stream will not be contant. If bandwidth is not an issue, variable bit rates are generally preferred.

Video Chroma Subsampling

Chroma subsampling is a method used to encode videos by implementing less resolution for color information than for black/white information. A common subsampling type used for videos is 4:2:0. Chroma subsampling takes advantage of the human's visual system's lower acuity for color differences than for black/white. Savely removing information that we can't notice saves bytes, resulting in lower file sizes.

Video Color Space

The color space is a mathematical representation of a range of colors. Common color spaces are RGB and YUV. YUV encodes a video taking human perception into account, allowing for reduced bandwidth and file size. It's doesn't make sense to show colors you can't see anyway, as compared to RGB.

Video Frame Rate

The frame rate determines the number of video frames per seconds (fps). Common rates are 23.98, 24 or 29.97 fps. A low frame rate results in a video appearing choppy or jerky. Higher frame rates are a pleasure to the eye, but comes with a higher file size.

File Size

The total size (in bytes) of the video. Higher file sizes require users to have a higher bandwidth. To avoid buffering or stalling, the file size (bytes) divided by the video duration (seconds) should not exceed the user's bandwidth (in Mbps).

File Format

The container is a format used to bundle the video and audio data into one file. Common containers are MPEG-4, WebM and QuickTime. In order to play the video, the browser or device must understand the container format to find out where the video and audio parts are located. MPEG-4 is supported by almost all browsers and devices. If you're serving the video in a different format, make sure your targeted device supports it. For example, serve videos in QuickTime formats only to Apple users.

File Extension

The file extension of the video file, for example: mp4. Publishers commonly have a restricted number of video file types they accept.

Video Codec

The video codec is the algorithm used to encode the video. Common codecs are H.264 and VP9. In order to play, the browser or device must support the codec to decode the video. H.264 is supported by almost all browsers and devices. If you're serving the video with a different codec, make sure your targeted device supports it.

MOOV Atom Location

The MP4 format consists of atoms (packets of data), that are arranged in a particular order. The MOOV atom acts like a table of contents for the video. In order for the video to start playing, the MOOV atom has to be read first. If that atom is located at the end of the file, the whole file has to be downloaded before playback can begin. On slow networks, users may have to wait a couple of seconds depending on the size of the video. For the video to start playing immediately, the MOOV atom has to be placed at the beginning of the file.

Delivery Type

The delivery type determines how the video is downloaded during playback. Either progressive or streaming. With progressive delivery, the video is actually downloaded to the user's device. It starts playing as soon as the necessary data is available. Streaming delivery requires a streaming server that only sends the part of the video that is currently watched. For most use cases, progressive delivery is the standard. If you're working with CTV or live-streams, the delivery type should be set to streaming.

Skip Offset

The skip offset determines after how many seconds the user can skip the ad and play the main content. A common offset is 15 seconds. If the publisher requires a skip offset, this test makes sure it has been configured correctly.

Video Mime-Type

The mime-type is a two-part identifier for file formats transmitted over the internet. For an MP4 file, it's video/mp4. The mime type should correspond with the actual file format. This test makes sure MP4 files have a video/mp4 mime-type, and similarly WebM a video/webm mime-type.

Stefan von Gartzen
Senior Adtech Specialist, Motor Presse Stuttgart

Ad Validation - Automated & Scalable

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