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VAST Video Ads in H.264 vs H.265. Does it all matter?

Written by Roy
Apr 5, 2022 • 4 min read
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Video & VAST
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VAST Video ads are generally encoded in an MP4 container to facilitate browser support across devices. Inside this container, H.264 has been the industry standard for many years to compress video data.

Since 2013, a newer standard called H.265 or High Efficiency Video Coding (HEVC) is on the rise, offering higher compression rates and lower file sizes. Should we all use the newer H.265 standard for VAST video ads?

Are you a publisher serving pre-roll video ads from your advertisers? Read on to learn why a QA check on VAST tags is indispensable to make sure the video plays correctly on all devices (and to increase your revenue).

How can I check if a VAST video is encoded in H.264?

You have two options here:

  • Open the VAST tag, download the MP4 video to your computer and open it in VLC Media Player. Go to Tools arrow_forward Codec Information and check the video codec of the first stream.
  • Use this QA scanner for VAST Video ads to automatically detect the video codec used. Enter your VAST tag URL and standard the scan. Within seconds you'll get a quality assurance report indicting the video codec used. You can configure the scan to let the test fail when an MP4 video is not encoded in H.264.

Why was a new standard developed?

Have you ever watched a high quality video where a frame freezes for a second, with visual artifacts and images 'smeared out' for a moment? The new H.265 standard was designed to address exactly this issue, along with other improvements for modern hardware. It also comes with better compression rates, requiring less bandwidth when send over a line. You can expect a reduction in file size of up to 50% compared to H.264. The new standard also supports parallel decoding on multiple CPU cores.

Network bandwidth comparison

Typically, H.264 requires more bandwidth for the same high-resolution video as compared to H.265. A 4K video encoded in the old standard requires around 32 Mbps, while the new standard requires only about 15 Mbps.

It's evident that the new standard will be part of the future. Let's compare bandwidth requirements in more detail:

480p1.5 Mbps0.75 Mbps
720p3 Mbps1.5 Mbps
1080p6 Mbps3 Mbps
4k32 Mbps15 Mbps

Should we all use H.265 for VAST video ads?

Short answer: no. The main reason is browser support. While the older H.264 standard is supported by almost all browsers, the newer H.265 standard is not ubiquitously supported yet. Even Chrome 90+ doesn't support it (year 2021).

Let's take a look at support for H.264 as shown on Caniuse. It's supported on 97.78% of all browsers.


The newer H.265 standard is only supported on Apple devices and reaches only 19.18% of all internet users.


What happens if I serve H.265 videos to Chrome users?

Then the video simply remains black and doesn't play. It's a wasted opportunity for both the publisher as well as the advertiser. It's therefore indispensable for Ad Ops to make sure the video is encoded in the correct format.


The current industry standard is not going anywhere soon. As long as browser support for H.265 remains poor, VAST videos should be encoded in H.264 to make sure it plays correctly across all browsers and devices.

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