I know people are anxious to see what happens next with my toy VP8 encoder. First and foremost, I corrected the encoder’s DC prediction. A lot of rules govern that mode and if you don’t have it right, error cascades through the image. Now the encoder and decoder both agree on every fine detail of the bitstream syntax and rendering thereof. It still encodes to a neo-impressionist mosaic piece, but at least I’ve ironed the bugs out of this phase:

I also made it possible to adjust the quantization levels inside the encoder. This means that I’m finally getting some compression out of the thing, vs. the original approach of hardcoding the minimum quantizers.

So I’m stubbornly plugging away at my toy VP8 encoder and I managed to produce this gem. See if you can spot the subtle mistake:

The misplaced color plane resulted from using the luma plane stride where it was not appropriate. I fixed that and now chroma planes are wired to use to the same naive prediction algorithm as the luma plane.

Also, I fixed the entropy encoder so that end of block conditions are signaled correctly (instead of my original, suboptimal hack to just encode all zeros). I was disappointed to see that this did not result in a major compression improvement. Then again, I’m using the lowest possible quantization settings for this outing, so perhaps this is to be expected.

Sigh… 4×4 luma prediction is next. Wish me luck.

I’ve been toiling away as a multimedia technology generalist for so long that it’s easy for me to forget that not everyone is as versed in the minutiae of the domain as I am. But I recently experienced what it’s like to be such an outsider when I posted about my toy VP8 encoder, expressing that it’s one of the hardest things I have ever tried to do. I heard from a number of people who do have extensive experience in video encoding, particularly with the H.264 and VP8 codecs. Their reactions were predictable: What’s so hard? Look, you might be a little too immersed in the area to really understand a relative beginner’s perspective.

And to all the people who suggested that I should get the encoder into FFmpeg ASAP: Are you crazy?! Did you see what the first pass of the encoder produced? Do you have lower standards than even I do?

Not Giving Up
I worked a little more on the toy encoder. Remember that the above image is what I’m hoping to encode somewhat faithfully for this experiment. In my first pass, I attempted vertical prediction for all planes. For my next pass, I forced the chroma planes to mid-level (which results in a greyscale image) and played with the 16×16 luma prediction modes. When implementing an extremely naive algorithm to decide which 16×16 prediction mode would be the best for a particular block, this is what the program produced:

For fun, here is what the image encodes to when forcing various prediction modes:
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I traveled to a secret clubhouse today to take part in a clandestine meeting to discuss exactly how WebM will rule over all that you see and hear on the web. I can’t really talk about it. But I can show you the cool hat I got:

Yeah, you’re jealous.

The back of the hat has an Easter egg for video codec nerds– the original Duck Corporation logo (On2′s original name):

Former employees of On2 (now Googlers) were well-represented. It was an emotional day of closure as I met the person — the only person to date — who contacted me with a legal threat so many years ago. He still remembered me too.

I met a lot of people involved in creating various Duck and On2 codecs and learned a lot of history and lore behind then– history I hope to be able to document one day.

I’m glad I got that first rough draft of a toy VP8 encoder done in time for the meeting. It was the subject of much mirth.

I wanted to see if I could write an extremely basic VP8 encoder. It turned out to be one of the hardest endeavors I have ever attempted (and arguably one of the least successful).

Results
I started with the Big Buck Bunny title image:

And this is the best encoding that this experiment could yield:

Squint hard enough and you can totally make out the logo. Pretty silly effort, I know. It should also be noted that the resultant .webm file holding that single 400×225 image was 191324 bytes. When FFmpeg decoded it to a PNG, it was only 187200 bytes.

The Story
Remember my post about a naive SVQ1 encoder? Long story short, I set out to do the same thing with VP8. (I wanted to do the same thing with VP3/Theora for years. But take a good look at what it would entail to create even the most basic bitstream. As involved as VP8 may be, its bitstream is absolutely trivial compared to VP3/Theora.)
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Yesterday, Google released a new still image format called WebP. To those skilled in the art, this new format will be recognizable as a single VP8 golden frame with a 20-byte header slapped on the front (and maybe a little metadata thrown in for good measure). We have a MultimediaWiki page and a sample ready to go.

Further, I submitted a patch to ffmpeg-devel for FFmpeg’s img2 handling system to decode these files. FFmpeg should support processing these files soon… if anyone cares. This leads into…

The Point, or Lack Thereof
Since yesterday’s release, I have read a whirlwind of commentary about this format, much of it critical and of the “what’s the point?” variety. For my part, I can respect academic exercises, a.k.a., just trying random stuff to see if you can make it work. That’s pretty much this blog’s entire raison d’être. But WebP transcends mere academic exercise; Google seems to be trying to push it as a new web standard. I don’t see how the format can go anywhere based on criticisms raised elsewhere — e.g., see Dark Shikari’s thoughtful write-up — which basically boil down to WebP not solving any real problems, technical, legal, or otherwise.

How did WebP come to be? I strongly suspect some engineers noticed that JPEG is roughly the same as an MPEG-1 intraframe, so why not create a new still frame format based on VP8 intraframes? Again, I can respect that thinking– I have pondered how a still image format would perform if based on VP3/Theora or Sorenson Video 1.

Technically
Google claims a significant size savings for WebP vs. standard JPEG. Assuming that’s true (and there will be no shortage of blog posts to the contrary), it will still be some time before WebP support will find its way into the majority of the web browser population.

But this got me thinking about possible interim solutions. A website could store images compressed in both formats if it so chose. Then it could serve up a WebM image if the browser could support it, as indicated by the ‘Accept’ header in the HTTP request. It seems that a website might have to reference a generic image name such as <img src="some-picture.image">; the web server would have to recognize the .image extension and map it to either a .jpg or a .webp image depending on what the browser claims it is capable of displaying.

Leftovers
I appreciate that Dark Shikari has once again stuck his neck out and made a valiant — though often futile — effort to educate the internet’s masses. I long ago resigned myself to the fact that many people aren’t going to understand many of the most basic issues surrounding multimedia technology (i.e., moving pictures synchronized with audio). But apparently, this extends to still image formats as well. It was simultaneously humorous and disheartening to see commenters who don’t even understand the application of, e.g., PNG vs. JPEG: Ahem, “We already have a great replacement for jpg: .PNG”. Coupled with the typical accusations of MPEG tribalism, I remain impressed D. Shikari finds the will to bother.

Still, I appreciate that the discussion has introduced me to some new image formats of which I was previously unaware, such as PGF and JPEG XR.