Digital Foundry vs. OnLive

Video Quality

Whatever OnLive might say about how revolutionary its approach to video compression is, the bottom line is that its HD service streams at about 5mbps. As the intended aim is to give you 60FPS video, the mathematics are incontestable. That's about 10K per frame as an average, including audio. For those with capped bandwidth allowances, OnLive consumes around 2.5GB per hour.

Conversely, an uncompressed 720p60 stream of data from the HDMI port of your console is around 2.6MB per frame, not including audio. So how does OnLive manage to compress so much into so little?

First off, the precision of the framebuffer is reduced. The 24-bit RGB format is gone in exchange for the same YUV 4:2:0 pixel format used by Blu-ray. Colour resolution is effectively halved in the transition. Even if bandwidth was increased tenfold, that wouldn't change without a fundamental change to the video codec. As a result of all that, OnLive at its best still looks rather washed out compared to the native experience.

Next up, every single frame produced by your console or PC graphics card is a keyframe, a distinct entity in of itself. OnLive uses shared information from previous frames in order to save the duplication of data, the same as any conventional video codec. While the company claims to have moved beyond this so-called "group of pictures" (GOP) format (and perhaps it has), the end result looks much the same. In scenes where there is not much movement, more information from previous frames can be re-used, resulting in a higher-quality image. In scenes with fast motion, less information is shared, meaning a collapse in picture integrity. The faster the picture changes, the more detail that 10K per frame needs to magic up from nowhere.

So how does this look in practise? How can we give you an indication of OnLive video using h264 streaming? Simple, we use our normal Face-Off methodology of slowing down video, then using an extreme h264 encoding method to make the most of those bits. Remember to use the full-screen button to get the full HD resolution - there's not much point watching otherwise.

In an ideal world, OnLive's bandwidth requirements would scale up depending on the complexity of the image to provide a constant level of quality. In the real world, that would produce video that would sometimes exceed ten times OnLive's current throughput, depending on the quality level you set, so it's just not viable. The result is that video quality is hugely variable in OnLive, ranging from very good to absolutely, diabolically dreadful. You will never get that disparity of performance on a local system.

That is not to say that OnLive cannot look pretty decent on a fairly consistent basis. A case in point is Batman: Arkham Asylum. The game is strongly suited to video compression as the action isn't operating at a breakneck speed, there's plenty of repetition from frame to frame, and the colour scheme is very muted. Cut-scenes in particular can look very good. So let's put the OnLive rendition of the game up against the PC version and see what we can see. There's a video below (remember to use the full screen button) along with a 720p comparison gallery.

Not bad. Still nowhere near pristine, but let's say you're gaming from range in the lounge: the difference in video quality is unlikely to be that noticeable or indeed upsetting. So let's up the ante a bit with a spot of Assassin's Creed: brighter colour schemes and far more intricate artwork and a step-up in terms of the pace of the game. Once again there's both the video below plus HD comparison gallery.

Here the video compression scheme is far less capable of retaining the quality of the original scene, directly impacting enjoyment of the game. Detail vanishes at the drop of a hat, and even between frames the quality of the image can vary enormously. However, image quality is given a boost through the game's extensive use of depth of field. Blurring background detail is just the sort of thing that the OnLive encoder likes.

A good rule of thumb with OnLive picture quality (and indeed streaming video in general) is that the more the image changes from one frame to the next, the lower the quality of the resultant encoded image. So, third-person adventure titles like Assassin's Creed II, Prince of Persia: The Forgotten Sands, Splinter Cell: Conviction and Batman: Arkham Asylum are pretty good picks on OnLive's behalf, in theory. However, racing games and twitch-based first person shooters are shifting the entire world view pretty much every frame, so the picture quality looks poor whenever you're in motion, which is most of the time.

In motion, DiRT simply looks muddy, ill-defined and jerky (more on that in the performance section), while UTIII poses real questions about the game's playability: the ability to pick out sniping opponents at long range while in motion would certainly be quite useful and yet there's a strong possibility that they would be merged into a sea of video compression artifacts in OnLive.

Overall, OnLive's massively variable picture quality is symptomatic of taking an existing video compression scheme and tweaking it extensively but still using the same fundamental principles and hoping for the best. It's fine in some cases, but clearly a lot worse in others and the real problem is that there is no consistency; the system simply isn't robust enough to cope with the infinite visual possibilities that gameplay offers, to the point where you have to wonder if the artists who created the game assets are going to be happy having their work stripped down to the macroblock level by the system's video encoder when the action becomes difficult to compress.

There's also the issue of whether OnLive can really claim to offer a high-definition gaming service. Yes, when you're standing still, or if there is very little motion, or if the game is chiefly composed of very muted colours, you can reasonably call the image "HD", but when fast motion kills off the quality so dramatically, it's easy to believe that the picture quality often falls short even by 480p standards in terms of actual detail resolved. You can see for yourself by checking out some more assets we've prepared: Splinter Cell and DiRT 2 screenshot galleries.

Put it this way, if Blu-ray was so visually variable and so frequently ugly, nobody would be upgrading from standard definition DVDs. At the very least, players should be thankful that OnLive features playable demos for the vast majority of its content: video compression will vary enormously and dramatically from game to game, from moment to moment, from frame to frame even. The demos at least will at least give you some idea if your gameplay experience is being excessively gimped by the video encoding.

The weird thing is that OnLive is talking about upgrading to 1080p in 2011. This will inevitably require more bandwidth, and if that's the case, it really should be thinking about offering the option to use that throughput for improving 720p image quality, and in effect brute force through higher IQ. In many cases it clearly needs it.