[theora-dev] Fast quality reduction transcoding

[Tim Starling]

Hi,

After a quick read of the Theora spec, I became curious about the 
possibility of fast quality reduction of Theora videos. The idea is to 
decode through the Huffman and reverse prediction steps, and then to 
truncate the coefficients and reencode. My questions are:

* Is this a reasonable way to reduce the quality and bitrate of a 
stream? Will it be comparable in quality to a complete decode to YUV and 
re-encode at similar bitrate?
* Will it indeed be much faster than a complete re-encode?
* How hard a task would it be to develop?

The application would be to have users upload high quality Theora videos 
to our website, and then to offer a selection of bitrates for download.

-- Tim Starling (Wikimedia Foundation)