On Sat, Apr 9, 2011 at 11:16 AM, Benjamin M. Schwartz <[email protected]> wrote: > On 04/09/2011 02:00 PM, Daniel Drake wrote: >> Ben, what are your thoughts on Theora vs WebM for Record? You >> mentioned at one point that Theora developers were considering >> focusing on the low-power arena (being displaced by WebM on the >> high-power high-res front), is that direction being taken? > > Essentially, yes. The WebM encoder (libvpx) has always been much slower > than libtheora because VP8 is much more computationally intensive than > Theora. The libtheora devs have been working to expand this difference by > adding encoder speed optimizations.
Google has also worked on speed optimizations for the vp8 encoder. The version of libvp8 included in Fedora 14, might be in updates-testing, includes these optimizations. You will see in my patch I am using speed setting 2 which is a single pass encoding meant for live streaming. I am so far very impressed with the system demands as well as the quality. With speed set to 2, and quality at 5 ( middle of the road ) I was able to record full 2 minute clips at Low Res, High Res, and also did some testing at 640x480. 400x300 recordings were using about 70-80% cpu utilization encoding in the WebM format. Google is also working on ARM optimizations that will be important for the XO 1.75 > > The latest versions of libtheora (1.2 alphas, and maybe even more in SVN > head) contain a lot of work to speed up encoding. I have recommended > several times that OLPC ship 1.2-prerelease libtheora in the default > build, due to the significant speed improvements. I did test this version out but found the improvements on our hardware to be marginal. I know there was talk about constant bit rate vs vbr possible needing to be tweaked. I didn't have the time to look into it then. > >> So encoding speed is quite a big deal > > Indeed. I don't see WebM as being a realistic option for Record until > OLPC gets WebM encoders in silicon, which will presumably be after XO-3. You can see in this video http://www.youtube.com/watch?v=ilmMrtlzSRg that the WebM on the XO 1.5 is really working better than our current release. You will hear a few pops in the audio, those points were when we would previously lose all sink between audio and video. In this video the sink isn't perfect but relatively close. Oh and there was a question about backwards compatibility. I know there would be work testing it, but I see no problems with backward compatibility. We would just have to check file types and adjust the pipeline accordingly. We would also have to adjust the mimetype properties to any Activities that may hard code them. -Jon _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
