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diff --git a/site/posts/11-raspberry-pi-madness.md b/site/posts/11-raspberry-pi-madness.md new file mode 100644 index 0000000..098d3fd --- /dev/null +++ b/site/posts/11-raspberry-pi-madness.md @@ -0,0 +1,163 @@ + + title: "Raspberry Pi madness" + permalink: '11-raspberry-pi-madness' + date: {m: 5, d: 26, y: 2017} + thumbnail: 'static/media/11-setup.png' + presentArt: true # ..this should probably be presentImage.. + categories: + - 'text' + - 'dev' + +--- + +# Raspberry Pi madness + +I got a Raspberry Pi, so, here's some rambling about it and what I've made +with it. + +First things first - the Raspberry Pi is *weird.* It's just funny having a tiny +little computer that can do pretty much anything (that isn't terribly +computationally powerful). I guess it's not too surprising, since mobile +devices are already way more powerful (and nearly smaller) than the Raspberry +Pi; but this thing feels a bit different, maybe because I'm actually able to +program it..? (But then there's Pythonista, too. Maybe it's the ability to +SSH into the box sitting on my desk?) + +It's also just fun to look at. I took a picture of it: + + + +(That picture looks an awful lot like an album cover.) + +Although my new setup is a bit less crazy (I got rid of the HDMI output, +keyboard and mouse). + +There's one distinct thing in that photo, though - the radio. I've got three +reasons for using that radio, instead of the HDMI TV output: + +**Reason one:** I don't want it to rely on HDMI, since sometimes HDMI might +not be available. + +**Reason two:** Radios give a nicer feeling. Having the radio speaker output +sound seems more friendly than a gigantic TV (and/or a dedicated monitor) +doing it. + +**Reason three:** I wasn't using the radio anyways. + +Okay, but, *what am I doing with it?* + +Short answer: it's playing my iTunes library. + +Long answer: it's downloading song files I have in my iTunes media folder and +playing those. No files are stored on the Raspberry Pi (except for the +currently playing track). I also made it be able to filter things by "group", +which really just means by artist and (optionally) album. + +..Ah, who am I kidding? This intro's way too long. I just want to show how it +actually works! + +--- + +## Generating the Playlist + +The first thing we need to do is create a file containing all the songs and the +URLs we can use to download them. I like using `python3 -m http.server` as my +main static server, because it only takes that one command to use, so we'll try +to parse the output of that. + +Thankfully, the format for directory listings with that server is relatively +simple; every `<a>` on the page links to a file or a deeper folder. Since we're +building a *tree* of the entire library (root -> artists -> albums), we'll need +to navigate the directory recursively; to do that we just run the crawl-folder +function on every `<a>` href-path that ends with `/`. + +Like I noted, the tree we end up with goes from the root folder, to a folder +for each artist, and then a folder for each of an artist's albums. + +There's actually a setting in the iTunes preferences that does all of that +sorting for us - under Advanced Preferences, "Keep iTunes Media folder +organized". That's enabled by default, I think. How convenient. + +I wrote the program that crawls the `python3` server in a separate file from +the main `play.js` script; `crawl-itunes.js`. In fact, it doesn't *require* +iTunes in any way; really it'll generate a tree for any `python3` (or similar) +server. (It probably won't work if the server gives parent-directory links, or +if there's links; it isn't built to deal with potential infinite recursion, +since that's not a problem in my case.) + +## Picking the Track + +Our playlist file essentially acts as a big listing of track titles and links +to the HTTP download for respective files; we'll use it to pick our song. +(That's what it's made for, after all!) + +The thing is, we want to randomly pick a track from all the tracks in our +playlist file. But our playlist file is a tree. We have two options here: + +* Recursively pick a random file or sub-group, until we hit a file. Use that. + +* Flatten the tree, then pick a random item. Use that. + +I went with the second option. The actual code behind it is boring, obviously, +so I won't bother going over it; but in summary we really are just flattening +the tree and picking a random item. + +Also, now's a good time to mention the optional "group path" option I made for +the program. If it's specified, the track-selector will only pick from tracks +under the passed group. (Sub-groups are split by `/`; so, for example, you +could make it only pick tracks from *Epic Battle Fantasy IV* by giving it the +group path string `'Phyrnna/Epic Battle Fantasy IV'`.) + +## Downloading the Music + +Before we can actually play anything, we'll need to download the track we want. +Just downloading the entire track before playing it works; the Raspberry Pi and +the device with the iTunes library are on the same network, so there's no +significant buffering. + +Our picked track playlist-item conveniently stores two pieces of information: +the title of the song[\*] and the download link for it. Clearly we'll need the +download link. It's just the HTTP URL we can fetch to download the track; so +that's what we do. + +[\*] Really the text between `<a href="..">` and `</a>`; not the actual +title of the track that's stored in the file's metadata. I'm too lazy to +figure out how to get that, plus I think some formats don't even have any +metadata of that sort. + +## Converting the Audio File + +Before we can actually play the file, we still need to do one thing. +Realistically, our files aren't going to all be in a format the play command +we're using will accept; we need to convert them to a standard format, like +WAV, first. + +That's not actually difficult, though. We can use `avconv`[\*] to convert the +downloaded file using a child process; that's just `avconv -y -i in out.wav`. +(`-y` is there to ignore any "should this file be overwritten?" prompts.) + +[\*] Originally I'd thought to use `ffmpeg`, but apparently that doesn't +actually exist as a proper package, and `avconv` is the more standard fork +people use. But it looks like `ffmpeg` and `avconv` work basically the same +way, at least to the user; so at least I didn't also have to learn a whole new +command-line program! + +## Playing the Audio File + +Playing the audio file is as easy as running the `play` command. In fact, +that's what we do! + +This step is actually that stupidly simple. It's literally just `play out.wav`. + +And then we loop back to picking another track! + +## What else can this do? + +I'd like to make a playlist file that somehow plays music from a YouTube +channel that has tons of music uploads; SiIvaGunner and HeavyMetal Rocker1988 +come to mind. That shouldn't be too hard to do, but it would probably mean +either making an in-between server that downloads and responds with the +downloaded YouTube audio (*stupid!*) or making the program work by downloading +YouTube audio, directly onto the Raspberry Pi (not stupid). + +Making it into an actual radio transmitter would be cool, too. |