Netflix is taking a closer look at an open-source HEVC encoder, x265, as well as Google’s libvpx, a software library for encoding its VP9 protocol, applying several quality metrics including its homegrown VMAF metric to see how well the two encoders performed in the SVOD provider’s streaming ecosystem.
“Our goal was to assess what can be achieved by encoding with practical codecs that can be deployed to a production pipeline, on the Netflix catalog of movies and TV shows, with encoding parameters that are useful to a streaming service,” the company said on its tech blog on Tuesday.
The result? The x265 encoder performed better than libvpx, reaching up to 50 percent bitrate savings – an amount that can halve the bandwidth required to send higher-resolution video over the internet, which is a concern with newer technologies like Ultra HD/4K and virtual reality video. The bitrate savings are similar to HEVC’s reported results, Netflix said.
“x265 and libvpx demonstrate superior compression performance compared to x264, with bitrate savings reaching up to 50% especially at the higher resolutions. x265 outperforms libvpx for almost all resolutions and quality metrics, but the performance gap narrows (or even reverses) at 1080p.”
Netflix engineers conducted the test using compute capacity provided via dynamic use of AWS servers reserved for the provider, along with its cloud-based encoding infrastructure. Some 5,000 clips of 12 seconds each were sampled from the Netflix catalog, from which more than 200 million encoded frames were created – encompassing “3 codecs, 2 configurations, 3 resolutions (480p, 720p and 1080p) and 8 quality levels per configuration-resolution pair.”
In addition to its open-source VMAF (Video Multimethod Assessment Fusion) metric, which Netflix created to better reflect human perception, making it easier to assess video quality across large swathes of data, the provider applied five other quality metrics.
Getting a handle on encoding is important to Netflix, whose video streams take up more than 36 percent of all U.S. internet bandwidth during peak traffic hours. With 4K content increasing on the SVOD service, delivery requirements will only go up – hence its ongoing quality tests.
- see this Netflix blog post
Netflix makes its encoding metric available as open source; AT&T and Chernin Group to launch SVOD bundle
Google developing VP10 encoding, promising to cut online video size by half again
Apple's fMP4 announcement at WWDC a 'significant step' for video encoding standards, Akamai says
4K gets thumbs down from Discovery, BBC and others at IBC