In-Depth Look At Video Codecs

johnsee writes "Atomicmpc has an incredibly in- depth look at a wide range of video codecs. It looks not only at their inner workings, but also shows the quality produced by each at a variety of settings and situations."

Comments

Uncompressed Codecs

[Doc Ruby]

The article makes some serious errors in overgeneralizations. It says that all codecs have in common that they make bitstreams shorter for transmission. But not all codecs compress (or otherwise reduce) their data. Some codecs transmit uncompressed raw data, increased in size by adding encoding data. For example, HD video monitors connected by HDMI (or DVI) use TDMS encoding not for compression, but to increase reliability in transmitting large raw data streams (10.2Gbps) quickly enough (340MHz) over cheap HW.

And though humans learned stone tools remarkable close to finally learning to load CD-ROMs, the stone tools were paleolithic ("old stone"), while the CDs were at worst neolithic ("new stone"). Someday we'll look at the modern era as a new age, probably "hualic", or "glass" age. These silicon chips and glass fibers have changed us as much as we've changed the glass from which we make them.

Just for kicks, I note that we've encoded the Si atoms into the new tools that define our age.

Image Algorithms

[Rac3r5]

Does anyone have a similar link to imaging and sound compression algorithms?

Re:Image Algorithms

[Rui del-Negro]

Yes, I was talking about stereo (which is still how >90% of music reaches the end users).

For audio production, lossy compression is a no-no (bandwidth and space are seldom issues), so there's no point in comparing lossy codecs.

For the vast majority of consumers, what matters is their perception of quality.

The point of quality comparisons is not to say "I recognise this version as the uncompressed one". It's to listen to several versions and pick the "best" one. And for that you don't need to know the piece at all. In fact, I'd argue that if you know a particular recording of that piece, you won't be judging abstract "quality"; you'll just be judging similarity to the version that you're used to.

In other words, like you say, (in a proper double-blind test), you'll only see consistent results if something "encodes really badly" (i.e., has obvious compression artifacts).

For image and video, where compression is often a requirement due to bandwidth and space issues (even during the production stages), it makes more sense to do comparisons to the original, rather than abstract "quality" evaluations. Which is not to say that consumer perception isn't still important. For instance, point & shoot digicams frequently over-saturate and over-sharpen images, because many consumers prefer that "look". Professional photographers prefer raw (or at least rawer) images, because they preserve more of the original information.

AVP beats ASP, no surprise.

[Kadin2048]

XviD is an H.263, aka MPEG-4 Part 2 "Advanced Simple Profile" (ASP) encoder, no?

This is quite different from the newer H.264 (MPEG-4 Part 10 "Advanced Video Profile" (AVP)) encoders like x264 (which is part of ffmpeg, at least recently, I believe). H.264 is a much better match for high-definition video that's going to be played back on HD equipment.

I think it's been known since the AVP codecs arrived on the scene that they pretty much kicked the crap out of the ASP ones; their only major downside is the processing requirements both to encode and decode, and (more true in the past than now) limited installed base of people with the codecs.

In this case, don't RTFA

[Rui del-Negro]

I've just read a bit of the article and the only thing I can think of is to paraphrase Stanislaw Lem: "it always amazes me that people need a license to drive a car but can write and publish all sort of nonsense without any clue about the subject".

His descriptions of "temporal compression" and "motion compensation" (to name just two of the fundamental building blocks of modern video codecs) are so wrong they don't even qualify as an error. He confused delta compression with motion compensation, thinks MPEG1 lacked the latter, doesn't understand why the former is virtually useless for video... sigh... even trolled Wikipedia articles manage to be more accurate than that.

I feel truly sorry for the people who read that and think they've learned something about the subject.

Re:In this case, don't RTFA

[Rui del-Negro]

God, I've just read his description of DCT. It's even worse. He seems to think that DCT consists of "dividing numbers by two" (he doesn't even use the word "quantization", that probably has too many syllables). And people complain about Wikipedia...

Time to shamelessly plug my articles about compression. Some parts are simplified (they're aimed at "end users") but, compared to this Atomic article, anything is flawless:

Lossless (data, image, audio)
http://digitalproducer.digitalmedianet.com/article s/viewarticle.jsp?id=106309

Lossy + Hybrid (image, audio)
http://digitalproducer.digitalmedianet.com/article s/viewarticle.jsp?id=109739

Video (lossless, lossy)
http://digitalproducer.digitalmedianet.com/article s/viewarticle.jsp?id=125089

The description of DCT is pretty funny

[Hoplite3]

I'm a bit skeptical of information in that article after reading the DCT description that described it as a rounding trick. What, is frequency-space too hard of a concept? Doesn't everyone get some Fourier analysis in college these days? You need to know it to be informed about a lot of modern data analysis.

Re:The description of DCT is pretty funny

[bodrell]

If you grabbed 1000 people at random - heck, I'll even give you 1000 people between the ages of 20 and 40, you'd be hard pressed to find 20 that have ever heard of DCT or Fourier analysis, and phenominally lucky to find one that could actually describe what it means.

Oh, and the answer to your question is "yes." Saying "Frequency Space" as part of a description to anyone who is not involved in either said data analysis, compression, or vibrations (my former, and sometimes current, field) is guaranteed to be met with a blank stare.

I first came across Fourier transforms in chemistry--specifically IR spectroscopy. I had the unfortunate experience of using a non-Fourier Transform Infrared Spectrometer (FTIR), a.k.a. a single-wavelength IR. It was a pain, and very time consuming, since the instrument scanned through each individual wavelength measuring absorbance of the sample. When I first used an FTIR, well, wow. It was explained to me that the FTIR measured all wavelengths at the same time, then crunched some numbers to calculate the absorbance at each wavelength. That's not so hard to understand for something that is time-invariant, but audio and video don't fit that description. That's why I'm still trying to figure out codecs, DCT, etc.

All chemical and electrical engineers, at the very least, know what frequency space is. Not just the small subset of occupations you mentioned. Wrapping one's brain around the Laplace transform is trickier than grasping the Fourier transform, in my opinion. The Dirac delta function is counterintuitive, to say the least. And frequency space--that at least has some physical sense. But s-space? WTF? It is only used to solve tricky differential equations, then you transform back into the time domain. If there is a physical interpretation for s-space, someone please correct me.

A wide range?

[jd]

I've seen more codecs on the back of a postage stamp. Seriously, one "modern", effectively one "old" (DivX and XviD are forks of the same original design), and one "archaic" does not make for much of a range. It doesn't even cover the spectrum of eras, never mind the spectrum of codecs.

For those who like laundry lists, here are some codecs not listed: Dirac, Theora, Huffyuv, Lempel-Ziv-Oberhumer Codec, MNG, Cell, NV, WaveCodec, Motion JPEG and MSU Lossless Video Codec. The wikipedia page doesn't list all of these, it took some scouting to find others and some of the early early ones are apparently only listed in the documentation on Open Source videoconferencing software I had back in the early 1990s.

Are any of these significant, though? Well, Dirac (BBC) damn well should be - we're only talking a high-definition TV quality codec by a major broadcaster with on-site offices in most countries that would be a logical choice for their remote bureaus to use and be a good candidate for competing with digital broadcasters in general.

Theora - well, it would be the ideal desktop videoconferencing codec in many ways. Those in common use today are heavier than necessary but the quality you buy with that at the bandwidth generally available just isn't worth it.

Huffyuv is said to be the fastest codec on the planet by some, which is entirely possible. That would make it good for most things where CPU power is expensive but bandwidth is cheap. (Embedded systems would probably fall into that category a lot.)

MSU's Lossless Codec is probably the slowest codec ever written, but gives by far the best compression. It makes a great reference codec to compare others against, apparently. If you could develop a decent hardware implementation, it might be a serious competitor to HD-DVD and Blu-Ray, as you could pack a comparable volume of material onto a standard DVD and therefore use already-existing commodity disks and players. All you'd need is a patch kit to add the decoder. This would likely appeal far more to consumers, as they wouldn't need to spend as much, but the studios and the manufacturers would hate and despise it for the same reason.

Non-Windows VC-1/WMA Pro playback

[benwaggoner]

Well, the OP was about how good codecs are :).

Actually, there are more non-Windows playback options than you think.

First, Flip4Mac can play back all VC-1 flavors and WMA Pro today. It doesn't play back the higher frequencies of WMA Pro, but they continually improve their support every release (full VC-1 Advanced Profile came in 2.1.1 last month). Downloading it seems pretty simple, but it isn't open source. And it nicely integrates with QuickTime, so once it's installed, WMV beccomes just another file format that QuickTime Player and the QuickTIme browser plugin can use. Can you go into some more detail as to why it's a painful option for you?

VLC 0.8.6 added WMV playback support, including VC-1. It's got some glitches around playing back B-frames, but I'm sure they'll address those. I haven't tried WMA Pro in it yet, I must admit.

Since VC-1 is a SMPTE standard, with full decoder reference source code avilable, adding decoding for it isn't harder than any other codec.

And of coures Silverlight will provide WMV playback on Mac and Windows as a browser plugin. We haven't committed to doing a Linux port post 1.0, but we've certainly gotten a lot of feedback from people who'd like to see it.