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Dirac vs. Theora

Dirac vs. Theora

Posted Apr 2, 2009 2:20 UTC (Thu) by ncm (subscriber, #165)
Parent article: New Theora encoder makes its first public release

I haven't been keeping track. Is there an encoder that pus a Dirac stream in an Ogg container? How does Dirac differ from Theora such as to lead one to choose one or the other? I presume that Theora holds it own in some ways or Tim wouldn't be working on it. Will they both be used indefinitely, or is one likely to be retired in favor of the other?


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Dirac vs. Theora

Posted Apr 2, 2009 4:33 UTC (Thu) by gmaxwell (guest, #30048) [Link]

Ffmpeg2dirac produces Ogg/Dirac(+Vorbis) files. These files should play out of the box on modern Linux distributions, they do on Fedora at least.

So, some comparison points:
* Dirac is able to achieve very high quality at accordingly high bitrates (it can even be run losslessly); Theora has a maximum quality which is not quite unconditionally visually lossless.
* Dirac is more cpu intensive than Theora.
* Dirac tools are somewhat less mature (In particular; there exists a decently performing Theora decoder in Java, which means that a majority of internet users can video Theora today with no software install)
* With the encoders existing today Theora clearly out-performs Dirac for low to moderate bitrates.

Which codec you should use today depends on your application. If you are archiving video, building a unencumbered-bluray, or squeezing production grade 1080 HD video into 270mbit SD channels, Dirac is what you want. If you are webcasting with under a couple of megabits per second, Theora is what you want— not only will it have better quality at the applicable bitrates, but you have more playback options. (Though you might also wish to offer a high quality dirac download option…)

For example— I recently put a Theora video online at http://www.celt-codec.org/presentations/ At 150kbit/sec Theora is perfectly adequate for this application while the slides are not always readable with the current Dirac 'Schroedinger' encoder at that bitrate. Yet a full resolution version at several megabits per second looks better in Dirac than Theora. Unless you're using Firefox 3.5beta the video is only playing for you on that page because the page is able to fall back from the the video tag to a java based decoder, something which isn't yet possible for Dirac. (And might never be reasonable due to CPU use?) I'm planning on putting up a Dirac download version… but I'm still playing around with the encoder. (…and it's a fact of life that no one manages to do multiple format parallel distribution well, myself included)

The gap between Theora and Dirac at the lower bitrate end of the spectrum may persist indefinitely as thats really what theora was designed for … future improvements to Dirac encoders may close the gap but it is difficult to speculate about that as that isn't an active area of development for Dirac today.

If I had to place a bet I'd guess that Dirac would continue to be used for "artefact free and better" video for the foreseeable future; the use of which will increase over time as IP transit costs decrease and bandwidth becomes more plentiful, while Theora will be obsoleted in a number of years by a replacement or an extension… It's only natural for lower bitrate distribution formats to have a shorter life compared to archive grade formats, and there is more to be gained from small improvements in formats used where every kilobit counts.


Dirac vs. Theora

Posted Apr 2, 2009 6:36 UTC (Thu) by DonDiego (guest, #24141) [Link]

> there exists a decently performing Theora decoder in Java, which means
> that a majority of internet users can video Theora today with no software
> install)

Who has Java installed in their browser these days? IME nobody, so where do you get these numbers from?

Dirac vs. Theora

Posted Apr 2, 2009 7:11 UTC (Thu) by gmaxwell (guest, #30048) [Link]

In this case my numbers, greatly hedged by simply claiming a majority, came from directly measuring many millions of visitors to Wikipedia.

It is true that Java penetration is in decline but it still ships as a standard pre-installed component on many systems and it is still is required for access to many business web applications. While the geekerati still hate Java, as they always have, Joe sixpack simply doesn't care. For all the same reasons that he has Flash he has Java. (and, in any case, Theora in Flash 10 VM appears completely possible— if anyone cares to do it… Vorbis is already done)

Dirac vs. Theora

Posted Apr 10, 2009 11:49 UTC (Fri) by robbe (subscriber, #16131) [Link]

> In this case my numbers [...] came from directly measuring many
> millions of visitors to Wikipedia.

Niiice argument. Do you have details (or a link thereto)? I confess, I'd
have questioned your statement (a little less belligerently), had not
DonDiego beat me to it.

> While the geekerati still hate Java, [...]

I think this mainly a thing of the past. It's FOSS goodness now, and the
alternatives are much worse.

Still, I fear that the decline of the Java applet will only accelerate.

Dirac vs. Theora

Posted Apr 2, 2009 4:55 UTC (Thu) by rillian (subscriber, #11344) [Link]

There are. You can use gstreamer, with the plugins from the schrodinger implementation, or the ffmpeg2dirac transcode application to put Dirac video in an Ogg container. The oggz tools suite also has support for splitting and remuxing Ogg Dirac streams. See diracvideo.org for pointers.

Theora and Dirac will coexist for some time. Theora requires fewer computational resources than Dirac, so it's more appropriate for lightweight devices. Theora does better at low bitrates and is a better choice for streaming and web-embedded video, while most of the effort with Dirac has focussed on high bitrate encoding, visually indistinguishable from the original--or even lossless--and is a better choice for production intermediates and high quality distribution. Theora has also been around a lot longer. It's a more mature format, with a bitstream frozen in 2004. Dirac's Ogg mapping was last revised something like six months ago.

So while Dirac will offer better compression in the long run, there are reasons to use each format today, and tomorrow. Neither is a replacement for the other.

Dirac vs. Theora

Posted Apr 2, 2009 6:12 UTC (Thu) by tajyrink (subscriber, #2750) [Link]

OggConvert is the nicest I know of, and readily available in eg. Debian repositories.


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