I jump around between projects. A lot. Over the years, I have employed various methods for retaining state or context as I switch to a different project. Here’s a quick survey and a general classification of their effectiveness.

Good

• Evernote: This is a cloud-based note-taking service that has a web client, Mac and Windows clients, and clients for just about ever mobile platform out there. I have an account and access it via the web interface as as the Windows, iOS, and Android clients. I really like it.

Okay

• Series of text files: I have been doing this for a very long time. I have many little note-filled directories here and there that are consistently migrated to new machines but generally forgotten about. This isn’t a terrible method but can be unwieldy when you work on lots of different machines. I’m still tracking down all these directories and importing them into Evernote.

Bad

• Layout of desktop windows: I have a habit of working on one project in a set of windows on one desktop space and another project in a second set of windows in another space, etc. Oh, this makes me shudder just thinking about it, mostly because of living in constant fear of a power failure or some other inadvertent reset (darn you, default config’d Windows Update) that wipes the state clean (sure, all of the work might have been saved, but I was relying on those windows to be set up in just the right manner to remind me of all the things I was working on). These days, I force myself to reboot at least once a week so I can’t get too deep into this habit. When it’s time to change projects, I write up exactly what I was doing and where I left off and stick it in Evernote.
• Open browser windows: I guess it’s common to have many, many tabs open in one’s web browser in this day and age. Like many, I use open tabs as a stack of items to read. The state problem comes when a few of the open tabs represent TODO items. Then I start living in fear that the browser might crash or be restarted in an unexpected way and I struggle to recall what 3-5 important TODO items were that I had opened in separate tabs (on top of a stack of less important items). Again, I try to shut down the browser frequently in order to break this tendency. TODO items are better filed in Evernote.
• Unsaved data in a text editor: Okay, this is just sloppy on my part, shoving temporary data into a text editor window thinking it’s supremely ephemeral. The problem comes when it’s linked to one of the many tasks on my desktop that might be bumped down a few priority levels; when finally returning to the context-free data, I’m at a loss to explain what it’s for. Evernote gets it, once more, with a more thorough description of what was going on.
• Email inbox: I make an effort to ensure that my email inbox has the fewest number of messages possible. Once things are dealt with, they get filed away elsewhere. This implies that things in my inbox require action. Some things have a habit of hanging around, though. Longer items now get described in better detail and filed away in Evernote.
• Classic paper: Thanks to Derek in the comments for reminding me of this one. Paper is a reliable standby but it can get unwieldy when Post-It Notes litter your work area. Further, it can be problematic when you have multiple physical work areas.
• Shell history: Another method I rely on entirely too often. This is when I count on a recipe of command line incantations living on in the history buffer of my Unix shell (generally Bash). What sequence of git commands allowed me to do XYZ? Let’s check the shell history– I sure hope it’s still in there.

Conclusion
I guess what I’m trying to say here is that I really like Evernote. If you have similar troubles with retaining state, try it out. I hear there are many other services similar to it with slightly varying feature sets (people rave about Microsoft OneNote). So there are plenty of options and something out there is surely a fit.

Evernote has a free tier and a premium tier. For my meager note-taking needs, I don’t come anywhere close to the free tier’s limit but I decided to pay for a premium subscription simply because I feel like I derive so much value from the service.

One downside, however, is that I seem to be doing a lot less blogging since I got on Evernote earlier this year (though it is where I author most of these posts nowadays; I especially like that I have a notebook labeled “Posted” whose incrementing count reminds me that I am getting some stuff out there). I originally started this blog as a sort of technical journal in order to organize notes and projects in a central location. It’s strange to think that if Evernote existed in 2005, I might never have had a reason to start this blog.

I bought an Android tablet a few months ago. It is less expensive than the best tablets but no where near the bottom end of the market. I think it’s pretty good. However, one downside is that it’s not “certified” to use Google’s official marketplace. That would seem to be somewhat limiting, however…

Enter Amazon’s Android App Store
Amazon got into the business of selling Android Apps some time ago. I started experimenting with this on a Nexus One phone that Google gave me. When I installed the App Store on the Android tablet and logged in, I was pleasantly surprised to see all of my Amazon apps ready for downloading onto the tablet.

So I have an App Store for use with this Android tablet.

Anyway, the reason I bring this up is because I managed to screw up this tablet in an unusual and humorous manner. You might be wondering if an app downloaded from the Amazon App Store requires the App Store to be present in order to run. The answer is: Oh yeah! It works like this:

This means that if — perhaps out of curiosity, for example — you login to the Amazon App Store, download an app, install it, and then subsequently log out of the App Store or uninstall it altogether, the downloaded app will decline to run until you log back into the store.

Here’s the thing– I wanted to provide a minimal level of security for my Android tablet. At the very least, I wished to lock the Amazon App Store itself since Amazon is famously (and, let’s face it, understandably) reluctant to deliberately add any friction to their shopping processes. I.e., without any external protection app, the App Store app would allow anyone to purchase any app using my tablet.

So I purchased App Protector Pro from the Amazon App Store and it worked quite well. By default, it also password protects against modifying any system settings as well as installing new apps.

So, here’s where I screwed up: App Protector Pro was doing its faithful duty and I uninstalled the Amazon App Store as an experiment. Suddenly, no apps obtained from the App Store would work unless I reinstalled the App Store. Okay, fair enough, except for one thing– App Protector Pro wouldn’t run without the App Store. Well, it did, it started to, tried to, but then exited. So I couldn’t re-install the App Store:

Oops

I eventually learned how to perform a factory reset of the unit which solved the problem. And, as indicated earlier, all of my apps were available for me to re-download.

Modding, Cyanogen-style
Open source aficionados will likely point out that there are alternate firmware options which allow me to take control of my Android tablet in a free and open manner. Among these options is CyanogenMod. After I got stuck in the situation described above, I thought I would have to resort to such an option.

On the plus side, researching alternative firmware options is what taught me to boot the device into a recovery mode and ultimately restore to a factory default setting. But if you’ll allow me to indulge in a mini-rant regarding accessibility of open source software: I was more than a little frustrated in trying to understand what CyanogenMod could possibly offer me. Their homepage says it’s “an aftermarket firmware”. I’m not entirely sure what that means or how it can benefit me. Fortunately, they have a full feature list linked from the front page. They are, in order: Lockscreen gestures, phone goggles, OpenVPN, incognito mode, themes support, and DSP equalizer. I can’t say that any of those really add any value for me. I’d love to know if CyanogenMod supports Google Android Market and various other Google apps (such as maps and GMail). That’s a question that I can’t seem to find the answer to.

The themes feature opens another old wound for me. Back around 1999 when I was first getting into Linux in a serious way, I remember that themes were a big theme at the Linux User Groups I would attend. I also remember lots are online articles at the time that emphasized how highly customizable the Linux desktop was in comparison to Windows 9x. I was bothered for 2 reasons: First, I thought there were more pressing problems that needed to be addressed in Linux; and second, none of these customization options seemed particularly straightforward; many apparently required hours of compiling and tinkering.

Small digression. Anyway, back to CyanogenMod, I was glad to see that they prominently display a button in order to “View Video Tour”. Ah, internet video has us so spoiled these days. I was eager to see this aftermarket firmware in action to see what it could do for me. However, the link leads to… a forum post? The thread seems to discuss how it would be a cool idea if the community could put together a video tour. At this point, the investigation just seems bizarre. It feels like a bunch of kids doing their best to do things the grown-up way.

Okay, sorry, rant over. I try to stay positive these days. I’m sure the CyanogenMod folks are doing great, fun, and interesting work on their project. The problems they choose to solve might lack mainstream appeal, however.

Free iPad
Ultimately, I recently unloaded the little Android tablet because, well… when a free iPad comes your way, lower spec tablets feel a little silly to keep around. Yeah, it’s great to play around with. Though here’s one unsettling thing I noticed about Apple’s App Store. While browsing for worthwhile games to indulge in, I noticed that they had a section for “Top Grossing Games”. This was a separate list from the “Top Apps” charts. I found the list weird for 2 reasons: 1) Why do I care which games are raking in the most cash? How does this communicate value to me, personally? Seriously, why would I base a purchasing decision around which vendor has earned the most money?

Anyway, let’s move on to reason #2 this was scary: Most of the games in this list had a price of FREE. One of them was that Capcom Smurfs game that stirred up controversy some months ago because of kids making unsupervised in-app purchases of virtual smurfberries. I tend to think that a top-grossing, free to play game is probably one that heavily encourages in-app purchases. Strange how this emerging trend actually encourages me to seek out games from the “top paid” list vs. “top free”.

A little while ago, I got a big head over the fact that I owned and controlled the feared and revered MPlayer samples archive. This is the repository that retains more than a decade of multimedia samples.

Conflict
Where once there was one multimedia project (FFmpeg), there are now 2 (also Libav). There were various political and technical snafus regarding the previous infrastructure. I volunteered to take over hosting the vast samples archive (53 GB at the time) at samples.mplayerhq.hu (s.mphq for this post).

However, a brand new server is online at samples.libav.org (s.libav for this post).

Policies
The server at s.libav will be the authoritative samples repository going forward. Why does s.libav receive the honor? Mostly by virtue of having more advanced features. My simple (yet bandwidth-rich) web hosting plan does not provide for rsync or anonymous FTP services, both of which have traditionally been essential for the samples server. In the course of hosting s.mphq for the past few months, a few more discrepancies have come to light– apparently, the symlinks weren’t properly replicated. And perhaps most unusual is that if a directory contains a README file, it won’t be displayed in the directory listing (which frustrated me greatly when I couldn’t find this README file that I carefully and lovingly crafted years ago).

The s.mphq archive will continue to exist — nay, must exist — going forward since there are years’ worth of web links pointing into it. I’ll likely set up a mirroring script that periodically (daily) rsyncs from s.libav to my local machine and then uses lftp (the best facility I have available) to mirror the files up to s.mphq.

Also, since we’re starting fresh with a new upload directory, I think we need to be far more ruthless about policing its content. This means making sure that anything that is uploaded has an accompanying file which explains why it’s there and ideally links the sample to a bug report somewhere. No explanation = sample terminated.

RSS
I think it would be nifty to have an RSS feed that shows the latest samples to appear in the repository. I figure that I can use the Unix ‘find’ command on my local repository in concert with something like PyRSS2Gen to accomplish this goal.

Monetization
In the few months that I have been managing the repository, I have had numerous requests for permission to leech the entire collection in one recursive web-suck. These requests often from commercial organizations who wish to test their multimedia product on a large corpus of diverse samples. Personally, I believe the archive makes a rather poor corpus for such an endeavor, but so be it. Go ahead; hosting this archive barely makes a dent in my fairly low-end web hosting plan. However, at least one person indicated that it might be easier to mail a hard drive to me, have me copy it, and send it back.

This got me thinking about monetization opportunities. Perhaps, I should provide a service to send HDs filled with samples for the cost of the HD, shipping, and a small donation to the multimedia projects. I immediately realized that that is precisely the point at which the vast multimedia samples archive — with all of its media of questionable fair use status — would officially run afoul of copyright laws.

Which brings me to…

Clean Up
I think we need to clean up some samples, starting with the ones that were marked not-readable in the old repository. Apparently, some ‘samples’ were, e.g., full anime videos and were responsible for a large bandwidth burden when linked from various sources.

We multimedia nerds are a hoarding lot, never willing to throw anything away. This will probably the most challenging proposal to implement.

I played with the ‘file’ utility a long time ago because I wanted to make it recognize a large number of multimedia formats. I had trouble getting my changes to take. But I’m prepared to try again after many years.

Aiming at the Corpus
In my local mirror of the MPlayerHQ samples archive, I find 9853 unique files. So I run all of them through the ‘file’ command:

  'find /path/to/samples -type f -print0 | xargs -0 file --no-pad'

My Ubuntu installation has file v5.04. I also tested against 5.07 and the latest, 5.08. Here is the number of files each version was unable to identify (generically marking as ‘data’):

5.04  1521
5.07  1405
5.08  1501

That seems like a regression for v5.08 until I dug into the details and saw quite a few items like this, indicating that the MPEG detection could use some work:

-mov/mov-demux-infinite-loop.mpg: DOS-executable (
+mov/mov-demux-infinite-loop.mpg: data
-image-samples/UNeedQT4.pntg: DOS-executable (
+image-samples/UNeedQT4.pntg: data

Workflow
These are just notes to myself and perhaps anyone else who wants to add new file formats to be identified by the ‘file’ command.

First, download either the latest release from the FTP or clone from Github. Do the usual unpack, ‘./configure’, ‘make’ routine. To use this newly-built version and its associated magic file:

  ./src/file --magic-file magic/magic.mgc <file>

To add a new format for ID, first, run the foregoing command to ensure that it’s not already identified. Then, check over the files in magic/Magdir and see which one might pertain to what you’re doing (it’s unlikely that your format will merit a new file in this directory). For example, for this round, I modified animation, audio, iff, and riff. Add or modify existing specs based on the copious examples in the directory and by consulting the appropriate man page (‘man 5 magic’).

Finally, run ‘make’ again which will regenerate the magic file. Invoke the above command again to use the modified magic file.

Before and After
On a selection of formats taken from the samples archive (renamed and cut down to a kilobyte because detection typically only relies on the first few bytes), here is the “before”:

amv:            RIFF (little-endian) data
armovie:        data
bbc-dirac:      data
interplay-mve:  data
mtv:            data
nintendo-thp:   data
nullsoft-video: data
redcode:        data
sega-film:      data
smacker:        data
trueaudio:      data
vqa:            IFF data
wavpack:        data
wc3-mve:        IFF data
wtv:            data

And the “after”:

amv:            RIFF (little-endian) data, AMV
armovie:        ARMovie
bbc-dirac:      BBC Dirac Video
interplay-mve:  Interplay MVE Movie
mtv:            MTV Multimedia File
nintendo-thp:   Nintendo THP Multimedia
nullsoft-video: Nullsoft Video
redcode:        REDCode Video
sega-film:      Sega FILM/CPK Multimedia, 320 x 224
smacker:        RAD Game Tools Smacker Multimedia version 2, 320 x 200, 100 frames
trueaudio:      True Audio Lossless Audio
vqa:            IFF data, Westwood Studios VQA Multimedia, 418 video frames, 320 x 200
wavpack:        WavPack Lossless Audio
wc3-mve:        IFF data, Wing Commander III Video, PC version
wtv:            Windows Television DVR Media

After rerunning ‘file’ on the mphq corpus using the modified magic file, only 1329 files remain unidentified (down from 1501).

Going Forward
As mentioned, MPEG detection could probably be strengthened. However, a major weakness is QuickTime/MP4. Many files are not detected, probably owing to the many ways that QuickTime files can begin.

I have never claimed to be especially proficient at math. I did take Advanced Placement calculus in my senior year of high school. While digging through some boxes, I found an old grade report from that high school year. I wondered what motivated me to save it. Maybe it’s because it offered this clue as to why I can’t perform adequately in math class:

Mystery solved: I did not wear proper P.E. attire to calculus class.

Sometimes, when I don’t feel like doing anything else, I look at that Apple SMC video encoder again.

8-bit Encoding
When I last worked on the encoder, I couldn’t get the 8-color mode working correctly, even though the similar 2- and 4-color modes were working fine. I chalked the problem up to the extreme weirdness in the packing method unique to the 8-color mode. Remarkably, I had that logic correct the first time around. The real problem turned out to be with the 8-color cache and it was due to the vagaries of 64-bit math in C. Bit shifting an unsigned 8-bit quantity implicitly results in a signed 32-bit quantity, or so I discovered.

Anyway, the 8-color encoding works correctly, thus shaving a few more bytes off the encoding size.

Encoding Scheme Oddities
The next step is to encode runs of data. This is where I noticed some algorithmic oddities in the scheme that I never really noticed before. There are 1-, 2-, 4-, 8-, and 16-color modes. Each mode allows encoding from 1-256 blocks of that same encoding. For example, the byte sequence:

  0x62 0x45

Specifies that the next 3 4×4 blocks are encoded with single-color mode (of byte 0×62, high nibble is encoding mode and low nibble is count-1 blocks) and the palette color to be used is 0×45. Further, opcode 0×70 is the same except the following byte allows for specifying more than 16 (i.e., up to 256) blocks shall be encoded in the same matter. In light of this repeat functionality being built into the rendering opcodes, I’m puzzled by the existence of the repeat block opcodes. There are opcodes to repeat the prior block up to 256 times, and there are opcodes to repeat the prior pair of blocks up to 256 times.

So my quandary is: What would the repeat opcodes be used for? I hacked the FFmpeg / Libav SMC decoder to output a histogram of which opcodes are used. The repeat pair opcodes are never seen. However, the single-repeat opcodes are used a few times.

Puzzle Solved?
I’m glad I wrote this post. Just as I was about to hit “Publish”, I think I figured it out. I haven’t mentioned the skip opcodes yet– there are opcodes that specify that 1-256 4×4 blocks are unchanged from the previous frame. Conceivably, a block could be unchanged from the previous frame and then repeated 1-256 times from there.

That’s something I hadn’t thought of up to this point for my proposed algorithm and will require a little more work.

Further reading

• My first entry regarding my toy SMC encoder

How do you take a 24-bit RGB image and convert it to an 8-bit paletted image for the purpose of compression using a codec that requires 8-bit input images? Seems simple enough and that’s what I’m tackling in this post.

Ask FFmpeg/Libav To Do It
Ideally, FFmpeg / Libav should be able to handle this automatically. Indeed, FFmpeg used to be able to, at least at the time I wrote this post about ZMBV and was unhappy with FFmpeg’s default results. Somewhere along the line, FFmpeg and Libav lost the ability to do this. I suspect it got removed during some swscale refactoring.

Still, there’s no telling if the old system would have computed palettes correctly for QuickTime files.

Distance Approach
When I started writing my SMC video encoder, I needed to convert RGB (from PNG files) to PAL8 colorspace. The path of least resistance was to match the pixels in the input image to the default 256-color palette that QuickTime assumes (and is hardcoded into FFmpeg/Libav).

How to perform the matching? Find the palette entry that is closest to a given input pixel, where “closest” is the minimum distance as computed by the usual distance formula (square root of the sum of the squares of the diffs of all the components).

That means for each pixel in an image, check the pixel against 256 palette entries (early termination is possible if an acceptable threshold is met). As you might imagine, this can be a bit time-consuming. I wondered about a faster approach…

Lookup Table
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WARNING: This post is a bunch of nostalgia. Feel free to follow along if you recall the DOS days of the early-mid 1990s.

I finally let go of my Gravis Ultrasound MAX sound card a little while ago. It felt like the end of an era for me, even though I had scarcely used the card in recent memory.

The Beginning
What is the Gravis Ultrasound? Only the finest PC sound card from the classic DOS days. Back in the day (very early 1990s), most consumer PC sound cards were Yamaha OPL FM synthesizers paired with a basic digital to analog converter (DAC). Gravis, a company known for game controllers, dared to break with the dominant paradigm of Sound Blaster clones and create a sound card that had 32 digital channels.
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Remember Intel’s custom flavor of H.263 cleverly named I.263? I think I have finally found an application that used it thanks to a recent thrift shop raid– Intel Video Phone:

The root directory of the disc has 2 copies of an intro.avi video. One copy uses Intel Indeo 3 video and PCM audio. The other uses I.263 video and an undetermined (presumably Intel-proprietary) audio codec — RIFF id 0×0402 at a bitrate of 88 kbits/sec for stereo, 22 kHz audio. The latter video looks awful but is significantly smaller (like 4 MB vs. 25 MB).

This is the disc marked as “Send it to a friend…”. Here’s the way this concept was supposed to operate:

• You buy an Intel Video Phone Camera Pack (forgotten page courtesy of the Internet Archive) which includes a camera and 2 CDs.
• You install the camera and video phone software on your computer.
• You send the other CD to the person whom you want to be able to see your face when you’re teleconferencing with them.
• The other party installs the software.
• The 2 of you may make an internet phone call presumably using commodity PC microphones for the voice component; the person who doesn’t have a camera is able to see the person who does have a camera.
• In a cunning viral/network marketing strategy, Intel encourages the other party to buy the physical hardware as well so that they may broadcast their own visage back to the other person.

If you need further explanation, the intro lady does a great job:

I suspect I.263 was the video codec driving this since Indeo 3 would probably be inappropriate for real time video applications due to its vector quantizing algorithm.

So I’m watching a fairly recent music video for a song named “XXXO” from an artist named M.I.A. when I’m suddenly assaulted by this imagery:

… and I enter nervous convulsions. You see, while this might seem to be an odd video effect to the casual viewer, to a multimedia hacker, it appears to be deliberately antagonistic. To anyone who has written a video codec, this scene looks like an entire casserole of video bugs, combining creeping plane offsets errors, chroma problems, and interlacing havoc. The craziest part is to realize that this is probably some kind of standard video effect / filter type. Upon a repeat viewing, I realized that the entire video sort of looks like an amateur video editor’s first week using video software.

Elsewhere in the video, a YouTube-style video frame vortex highlights the proceedings. I guess I need to come to terms with the fact that the ubiquitous player frame is just part of the digital Zeitgeist now:

Vintage Video Strangeness
I’m a long-time music video junkie but I have a tendency of examining them entirely too closely. I first saw Paula Abdul’s video for “Cold-Hearted” when I was just starting to understand multimedia technology and how it interacted with emerging home computers. Imagine how confused I was when I tried to make sense of the actions performed by our eMaestro “Chuck” whom Paula has instructed to “hit it”. First, he hits a key followed by 3 quick strikes on a second key:

Then, the “start music” action is apparently bound to a particular key on the electronic keyboard:
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