Archive for January, 2008

Eureka

This is complete geekitude, so feel free to disregard…

I want to take a DVD, stick it in the drive and at some point have the smallest file possible that contains as much of the original structure as possible.

There are a few problems with most of how this is done most of the time. When you download a video off the internet there are several parts that go into that file. There’s the sound and the video streams and then a container that joins them all together. The container syncs the streams and says, this second of audio goes with this second of video.

The most common container format in use currently is AVI from Microsoft. AVI is a fairly old format and it has several limitations. One of the most important for my purposes is it pairs one video with one audio track. That’s fine when you’re encoding your home movies, but it can’t handle dubbing and director’s commentaries for DVDs.

There are a couple new formats to consider, but the one I like the most is Matroska. It’s flexible and supports not only the multiple audio streams but also multiple subtitles.

Inside the container there are even more standards at work. The raw data for audio waveforms and video images is huge. Different compressions schemes, called codecs, are used to compress the data and make it take up less space. They operate in a variety of ways, but ultimately the goal is a tradeoff between the degradation of the image or sound quality and the size of the output file.

Audio compression has seen a bit of improvement over the old workhorse MP3, but the real improvements in technology in recent years has been in the realm of video compression. H.264 is able to produce a file that is nearly visually identical to the MPEG-2 used on DVDs in fraction of the space.

There are some programs, notably HandBrake, that do a pretty good job of doing what I want. Before HandBrake was released however, I started on a ripping program of my own. I’ve been playing with it for a bit and this morning I had a bit of a breakthrough.

When I list the contents of the DVD, it tells me in general that the video is in NTSC. That makes sense, since NTSC is what we use here in America. The encoder was complaining though about dropping frames which shouldn’t happen if I was encoding at the right rate.

It turns out that though NTSC is 60000/1001 frames per second and interlaced every other frame NTSC is 30000/1001, movies are filmed at 24000/1001 and that is how they’re stored on progressive DVDs. In running my encoding previously at 29.97 and ending up with a file around 1500mb. I switched to 23.976 and the file size dropped by 500mb.

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etudiants

On the subject of grad school, I got the reviews from my teaching assistantship. Once a week I would give a recitation on some subject concerning ethics and computer science. All sorts of stuff from net neutrality to the history of hacking to the development of intellectual property law in America. I really enjoyed it. Unfortunately I also had to grade an essay per week for each of the 35 students and that was less entertaining.

I felt pretty good about the recitations. I’m about as geeky as anyone I know and this was essentially geek story time for an hour. My audience was 30 Malaysian students which was a bit challenging, but over the course of the semester I saw a real improvement in their critical thinking skills and writing proficiency. In the end that’s what I really enjoy about teaching.

I did wonder though about what they thought. After I’d stepped up the grading criteria on one of their essays, I asked them if they’d rather if I just saved us all some time, skipped reading the papers and just gave them all B+. All but two said “yes.”

I’ve been wanting to play with Google’s Charts API.

How helpful and responsive was the TA?

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How was the TA’s fairness in grading?

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Did the TA communicate effectively?

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What is your overall rating of the TA?

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After bleeding all over their papers and making them work fairly hard, I’m pretty cool with having 80%+ giving me good or excellent. I’d really like to get to teach a class like this at some point in the future. I would really like to see what could be done with it if it were treated as a persuasive writing and critical thinking class as much as a survey of ethics issues. Many of the students weren’t even really in a position to fully appreciate the issues they were introduced to and I think it would have been interesting to try and address that problem.

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Planification

My first semester as a graduate student has come and gone. It has certainly been a learning process.

So far as the amount of actual information I learned, it was acceptable. I had Human-Computer Interaction which primarily dealt with user interface tests for software development. I’d seen most of that in work before, but there was some bits about doing statistical analyses that were new and interesting.

Statistical Inference was my favorite class. It was also mostly a repeat of information I’d had before, but we had nice little tables instead of all that messy integrating. The different tests were new though and the review was useful. I also managed to get more of my notes types up this time which I figure will be useful in the future.

Artificial Intelligence was drudgery. They combined the grad and undergrad sections since one of the professors was off on sabbatical. The main difference ended up being huge amounts of homework. I’d certainly not claim that I didn’t learn anything, but the process was at times a bit frustrating.

All in all though I’m still happy with my decision to start this trip. Grad school in some ways aged me. Having two or three homework assignments that required 30-40 hours to complete over the course of two weeks actively sucked some of the fun out of me. It meant I spent quite a few nights at home while the_archange1 was out and about. I’d like to be able to say that when I had fun it was all the more intense, but honestly it wasn’t. The stress and the fatigue made me more boring, but I learned how to get a shitton of work done and that’s a skill I’ve been wanting for a while.

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