I spent most of the day working on a talk for Toastmasters; I want to illustrate it with short clips from a movie. There must be an easy way to mark two points in a MP4 file while you’re watching it and copy what’s between them into a new file, but I couldn’t find one – what I did find was this page which had shell scripts that did some computation, then called ffmpeg to perform the actual extraction. The scripts worked as advertised, but I wanted to make two improvements.

The first was to be able to supply sub-second timestamps for clipping; Bash can’t do decimal arithmetic, but the bc command can, and that was an easy change to make.

The other improvement I wanted to make was to avoid having to make a full copy of the source file with “key frames” added at the exact points I wanted to start and end the clip with. The original author was working with short files, but I was working with a full movie that was nearly 2GB in size – making a copy of such a file takes a while, even on a fast machine with an SSD.

I thought about it and came up with a workaround. I extracted a few seconds more than I wanted (without having to add key frames); then I put key frames in at the right points in the extracted video (which required copying it, but only a 10-15MB file, not multiple gigabytes); finally, I extracted the exact part I wanted.

This was easy, but it required multiple calls to bc to do the calculations. And I needed logic in shell script, which is not my strong suit. But I eventually beat it into submission, and it seems to work.

I realized afterwards that it would have been easy to write a short Python program to do the calculations and write out the exact commands I’d need – and there’d be a much better chance of understanding it if I ever had to modify it. But unless I run into yet another problem, I’m going to leave the code alone.

Having elegant code is nice, but going to sleep is better.

I was walking to the doctor about three weeks ago, enjoying the beautiful weather and the scenery – until I tripped over a discontinuity in the sidewalk and fell down hard enough that my watch wanted to call 911. I was mostly OK (though my pants didn’t survive the experience), so I picked myself up and continued on my way.

While we were visiting our son Jeff in Boston last week, we saw a dead rat in the Public Garden. Jeff stopped and took a picture, then he fired up Boston’s 311 app and reported it – the rat was removed the same day (and they told him they’d done so). I was impressed.

Today, Diane had to go to the same doctor I visited three weeks ago. We had to be out of the house this morning, so we walked there together. She asked me to point out where I’d fallen so she could avoid it on future visits. When we got there, I saw that the sidewalk hadn’t been repaired and was still a danger; I thought about Jeff and looked for a San Jose 311 app. I installed it and reported the problem, complete with picture.

I got a response within hours, telling me that my request was being forwarded to the city Department of Transportation. Not quite what I was hoping for, but maybe it’s a first step.