Blogging Theora

[xiphmont]

It's time for the latest Thusnelda encoder project update summary!

Although I haven't gotten much time to dive back into Thusnelda coding myself, Tim Terriberry, Greg Maxwell and others have continued the work along at a merry pace. In the past few weeks, they've finally replaced the leaky fDCT from the original VP3 and begun work on adjusting the main quantization matrices and, hopefully soon, adaptive quantization. These improvements all improve fine detail rendering and, somewhat unexpectedly, improve gradient rendering as well:

The screen caps above were produced by Theora 1.0 on the left and an experimental version of Thusnelda with early quant matrix optimization work in addition to the new fDCT on the right. Both clips were encoded in constant-quantizer mode and equal bitrates.

Other improvements, more details and the full update report here.

Comments

Re: Problem with older ffmpeg, not ffmpeg2theora

[xiphmont.livejournal.com]

...then why do we have so much trouble with it? Why does the demuxing have sync issues? Why can't it seek? Why can't it chain? Why does the muxing produce invalid files? Why is the built in vid output broken half the time? Why is the clipping rectangle wrong? The list goes on. And when we report problems, submit patches, we're told that there's nothing wrong (just like you've done). I trust ffmpeg about as far as I can throw it (despite using it practically every day, along with mplayer).

Frankly, I don't care about your 'world class' h264 support here. We're talking about Ogg, Vorbis and Theora. Great h264 doesn't fix bugs in Ogg.

As for the DCT, there's more information on the demo7 page (http://web.mit.edu/xiphmont/Public/theora/demo7.html).

Re: Problem with older ffmpeg, not ffmpeg2theora

[(Anonymous)]

Well, sorry about the imflamatory tone, but "the trouble they're having producing independent versions of any great quality" is going a bit overboard. The ogg de/muxers might be in bad shape, I wouldn't know (but I do know a few Ogg+Vorvis+Theora files I tested tend to play just fine.)

The inability to chain is a feature though :)

I've read the demo7 thing before but it doesn't answer my question. In the spec, section 7.9.3, the iDCT is specified, and it says "A compliant decoder MUST use the exact implementation of the inverse DCT defined in this specification."

So my question is whether improving the DCT implies changing the format, having to update the spec, and causing old files to play sightly differently (unless the decoder detects the encoder version and uses the same DCT).

It's not a big deal, I'm just curious.

Re: Problem with older ffmpeg, not ffmpeg2theora

[(Anonymous)]

Sorry for the spam, I got this wrong. The iDCT the decoder uses is unchanged, the one the encoder uses (the forward one) is the one that has been changed - in fact, to match more closely the inverse one.