Monday, December 28, 2009

x264: Encoding times for Baldur's Gate footage

While the Baldur's Gate game runs at a measly 640x480 screen size, it has a lot of dithering which can easily be washed out / muddied up by a low bitrate. So when encoding with x264, I recommend a decent CRF value (I'm currently using CRF 24). The major problems that you'll see are where a fireplace is present in a dithered / shadowed area (such as inside the Candlekeep Inn).

On the upside, a large portion of the screen rarely changes due to the large buttons along the left / right / bottom edges. So that simplifies the encoder's job.

The bitrate for the final file usually ends up in the 550-660 kilobits/sec range. Which is about 167:1 to 200:1 over the original FRAPS footage. At the upper end, that's around 4.8 megabytes per minute of footage (the lower end is 4.1 megabytes/minute). That includes a 130Kbps AC3 audio track, so the video portion is compressing down nicely.

Update: Later encodes are more in the range of 800-950Kbps due to lots of panning in outdoors areas. Which is more in the range of 5.5 to 6.7 megabytes per minute of footage. Or about 400MB per hour at the upper-end.

On my aging quad-core Phenom 2.5GHz machine, I'm seeing encoding speeds of 30-45 frames/sec which is a bit better then real time. However, the major impediment to maxing out all 4 cores seems to be disk accesses. So the CPUs are only working about 75-85% during the video encoding portion of the task. That's with a 750GB 7200RPM SATA drive. It would go faster if I was using a 10k RPM drive or a RAID-0 or RAID-10 array.

Labels: 2009, VideoEncoding, x264

posted by Wuphon's at 11:02 AM