Defining and Assessing Quality for Emerging Codecs
See the full video from this session, AV1: A Reality Check, on the Streaming Media YouTube channel.
Learn more about emerging codecs and streaming QoE at Streaming Media West 2020!
Read the complete transcript of this clip:
Vittorio Giovara: It's really hard to use the same quality definition that we've been using for AVC for this new generation of codecs--HEVC, VP9, et cetera. There should be really be more aspects to it than just resolution.
I'd like to introduce the three aspects of quality: the spatial, the temporal, and the spectral. The spatial is just increasing the resolution, which is the normal quality metric that we've mostly been using so far. Then there is the spatial, which is increasing the frame rate. The higher the frame rate, the better the image for the viewer. And then there is the latest one, the spectral, which is increasing the bit depth and improving the color space. In that regard, HDR has been the greatest and newest technology that has been available for video in the last few years.
Tim Siglin: I think that depth is very important, as you say, because the more bit depth you have to work with, the better off you are from the standpoint of actually perceiving the differences even between shades of black, et cetera. Nathan, you had mentioned something before we went on the air on the bit depth standpoint from AV1 having an internal bit depth that can be deeper than what is put in versus what's put out. Can you talk a little bit about that?
Nathan Egge: A lot of the quality artifacts that users see--they might see some very low-contrast areas with banding. There's a famous Game of Thrones scene, but I've also seen it in plenty of sky scenes, and that's really due to quantization error, right? One of the ways you can address this is, if you have a codec like AV1 that has a higher internal bit depth that it uses, that lets you avoid some of the heavy banding. Obviously, there are dynamic range issues and things like that. This is an area that was added in AV1 development that lets us have this higher internal bit depth path that should address that to some degree.
Tim Siglin: It's interesting that you described that because, having worked in motion picture, when we started using After Effects, we would bring in 8-bit content, we would process it at 12-bit because of concatenation issues and the like, and we'd be able to spit out something that was 8-bit that still had a better perceived quality. So that's really intriguing that that's built into the codec itself.
Bitmovin's Paul MacDougall discusses what determines perceptual visual quality and how it impacts quality of experience (QoE) for streaming viewers in this clip from a panel on the state of AV1 at Streaming Media East Connect 2020.