Quality comparison of Googles VP8 and x264 using "standard" video sequences.

VP8 and x264 comparison using VQM (visual quality metric), PSNR and SSIM evaluation.
Please consider also Jason Garrett-Glasers technical codec comparison.

Codecs

Command line options

If you think that different settings will make a big difference, feel free to suggest.

Video sources

I used all these CIF sequences.

Results

Target bit rate

The target bit rate is reached by both encoders quite good in average; local stability was not yet evaluated. VP8 tends to undershoot the bit rate a bit more for high target settings. There is also one outlier (VP8, Akiyo, target rate 1000 kbps); there is simply not enough information in this video to justify 1 Mbps.

(click on the picture to see bigger graph)
Target Bit Rate x264 / VP8

Visual quality metric as standardized in ITU-T J.144 and ITU-R BT.1683

The visual quality is measured using the NTIA general model, which was selected by VQEG and standardized by ANSI and ITU.
x264 outperforms VP8 here in almost all cases.
A VQM value of zero means: no visible difference to the original. So, smaller VQM is better.
VQM 100 kbps VQM 200 kbps VQM 500 kbps VQM 1000 kbps

PSNR & SSIM

Actually, considering only the standard metrics, the two current implementations are not that different. x264 has still an advantage in the current incarnation. The PSNR performance could be further "optimized" for x264 by using --tune-psnr, but that would degrade the VQM.
Encoding/decoding speed is a different issue (with clear advantages for x264/ffmpeg at the moment).

(click on the pictures to see detailed graphs)
Akiyo PSNR/SSIM Bridge (close) PSNR/SSIM Bridge (far) PSNR/SSIM Bus PSNR/SSIM Container PSNR/SSIM Coastguard PSNR/SSIM Flower PSNR/SSIM Football PSNR/SSIM Foreman PSNR/SSIM Hall PSNR/SSIM Highway PSNR/SSIM Mobile PSNR/SSIM Mother PSNR/SSIM News PSNR/SSIM Paris PSNR/SSIM Silent PSNR/SSIM Stefan PSNR/SSIM Tempete PSNR/SSIM Waterfall PSNR/SSIM

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