I’m constantly bombarded with RESTful stuff at work. So much so, that I’ve started rewriting RemotePi as a REST API. Lots of learning and reading, then.

As usual most of the literature was written by people who studied computer science. They just love abstractions. Solving problems is OK, as long as they get their daily hit of abstractions. So there are resources, verbs and routers. Very nice.

You’re supposed to refer to a resource without ugly queries in the URL. Instead, it should be just http://pi/remotepi/home/ for the media root directory. But how the hell does such an URL generate a query that can be processed by a CGI or FastCGI app?

The computer scientists are silent on the issue.

So I had to dig deeper and discover mod_rewrite of Apache2. There is a lot in a name. It rewrites incoming URL requests and is able to turn them into proper queries. Thank you Ludovico Fischer.

So here is my “resource router”.

First enabled mod_rewrite:

a2enmod rewrite
service apache2 restart

And the router config in /etc/apache/sites-available/default

RewriteEngine On
RewriteRule /remotepi/(.+) /remotepi/api.pl?$1

Very Perly, ain’t it? It’s because it uses the Perl regex engine.

RemotePi, the remote-control webb-app of my Raspberry Pi media center, felt sluggish. Until I measured the response time with Firefox WebDeveloper/Network. It’s now official: it was sluggish: it took 800 ms to respond. That’s nearly one second.

So it was time to turn the original CGI solution into a FastCGI one. Instead of firing up a new Perl process upon each request, the app keeps running in the background and replies requests in a main loop. I’m using Apache2 mod_fcgid.

The improvement is shocking: File browsing is about 25 ms, requests involving an omxd call take 80 ms. And that’s basically the pure runtime of the omxd command.

FastCGI is fast indeed.

To cut a long story short: YouTube finally works in HD on my TV with RemotePi. I can’t stop watching LaFerrari and McLaren P1 videos in HD with great sound!

Why was it so difficult?

In the old times, youtube-dl -g spat out YouTube stream URLs, and omxplayer could play them straight away. The excellent ncurses based yt worked this way. But things have changed. YouTube now only streams the video if a session cookie is presented. But omxplayer can’t use cookie jars.

But curl can! We tell youtube-dl to save the cookie, and let curl save/stream the video using the cookie.

curl -b jar `youtube-dl -g --cookies jar --write-thumbnail`

will spit out the video stream.

1st Attempt – Save to File

Let curl save to a file, and start omxplayer a few seconds later to play it back. Keep fingers crossed that curl saves faster than omxplayer reads.

It does not. This solution is so disk/sdcard IO intensive, that omxplayer will reach the EOF too soon and exit.

2nd Attempt – Stream via FIFO

Let’s create a FIFO file, and let curl write the video stream into that. And start omxplayer immediately to read the video stream from the FIFO. It works beautifully:

• there is no disk IO at all, so curl writes faster than omxplayer reads
• even if it’s not the case due to a slow network, the player does not exit, just blocks until curl catches up. Bacause the FIFO is a character device!
• if omxplayer exits for any reason, curl gets a SIGPIPE and exits too

The Result – rpyt

It’s all wrapped up in a new script packaged with omxd: rpyt.

And the RemotePi remote-control web-app also uses that from now. See the project homepage and the code on Github.

YouTube parties have a few flaws. Five to ten people gather around a small laptop, an even smaller tablet or a tiny smartphone. Nobody can see the screen really well. It’s no biggie, actually, as nobody cares for videos someone else wants to show. You only want to show off yours. And here is the problem:

You have to wait until the end of that lame boring clip, just to start the search for that brilliant masterpiece you’ve come across last night.

And that’s where remotepi and youtube-dl come for the help of the party, to fix the small problem and the big problem. First, the actual video is played on your huge flatscreen TV by the Raspberry Pi. Second, everyone can search for the next clip on their mobile phones in the meantime!

Head to the homepage or github.com/subogero/remotepi to solve your YouTube problems.

And why semi-ultimate? Erm, a few small problems. The omxd playlist daemon may or may not work properly with the freshest omxplayer. Also, a few video URLs can’t be played by the latter, probably due to authentication problems. But give it a try, anyway.

My Raspberry Pi media player suite has reached a generally usable level. At the bottom of the stack there is omxplayer, then the omxd playlist daemon, the rpi.fm command-line internet radio player and, finally, RemotePi the remote control web-app, optimized for smart-phone screens.

Check out its home page.

Why Not XBMC?

I admit I suffer from severe NIH (Not Invented Here) symptoms. But this time, I actually tried to install XBMC from Michael Gorven’s Debian package. But what do I see?

I need to get 44 MB of archives. 120 MB additional disk space will be used. RemotePi, rpi.fm and omxd are 3 MB including all sources, all binaries and all git repositories.

And lo and behold, who are among the dependencies?

• qt3
• mysql-common
• samba-common-bin

Come on! I never use my Raspberry’s GUI. All the GUI RemotePi has is a web-app.

MySQL? Probably a sign of a nice tag-based media library which, in real life, is an absolute pain in the neck to use. You have a DJ-set album, from all sorts of different artists, and a tag-based player just refuses to play it in the order intended by the DJ. I’ll stick to my files and directories, thank you very much.

Samba? I’m one of those smug Penguinistas whose home is Windows-free. So no thanks.

My Raspberry Pi media player suite.

RemotePi

Browse music/videos, internet radio stations and even YouTube on your Raspberry Pi and play them on your audio system or non-smart HDMI TV.

Control everything from your smartphone via the RemotePi web-app. You don’t need an extra remote control, you don’t need SSH, you don’t need to connect physically to the Raspberry Pi, and you definitely don’t need to start the GUI.

Features

RemotePi uses the omxd/omxplayer backend.

Show what omxd is playing now, including album art or YouTube thumbnail and actual/overall clip time.

Limit file browsing within the Raspberry Pi’s file system to a root directory specified in a config file /etc/remotepi.cfg.

Insert, add and append files, directories or internet radio streams to the omxd playlist.

You can even interrupt the playlist to play a single file or a YouTube clip. The playlist resumes after the end of the movie.

Control buttons: Play/pause/stop playback, or navigate in the playlist with repeat, previous/next, Rewind/FastForward 30/600s, or previous or next album buttons.

Delete actual track or entire playlist.

Cycle through subtitles and soundtracks, switch audio output to HDMI of Jack.

RemotePi is strictly file and directory based and could not care less for MP3 tags in files. It does not use 3rd party databases for metadata, except for internet radio. Best used with a nicely arranged folder structure.

Installation

Source code and installation instructions on Github.

Tecnology

RemotePi is a single HTML5 webpage, you load it once and then it communicates with the Raspberry Pi with AJAX calls using JavaScript. It won’t work it JavaScript is disabled.

youtube-dl

From rg3, RemotePi uses this program to extract direct stream links from YouTube page URLs. You can install it from Raspbian, as well.

rpi.fm

Who does not love internet radio stations? Who does not like to listen to Liquid Funk or Detroit Techno or Verdi all day long? Now you can do it easily on your Raspberry Pi. rpi.fm is an interactive command line tool that allows you to browse hundreds of genres and thousands of stations from the database of internet-radio.com.

Check out the details on Github.

rpi.fm also uses the omxd media player daemon for playback.

omxd

But what the hell is omxd, you may ask. Well, you probably know the brilliant omxplayer that plays full HD videos using the GPU of the Raspberry Pi. It has a few limitations, though. It can play only one file at a time, unless you are a scary shell-wizard.

Would not it be great, if you could add your entire music collection to its playlist in one step?

Would not it be great if you could log out of your SSH/GUI session and it would keep cranking out Psytekk?

Would not it be great to interrupt your music playlist, watch a movie, and continue your playlist where you left off, after Vincent Vega and Jules leave the restaurant?

Exactly. That’s what omxd, the omxplayer daemon does. Maintain, manipulate a playlist, and play it in the background. It’s the heart and soul of RemotePi and rpi.fm.

Check it out on Github.

Future Features

Debian packages for all three tools. So all you have to do for installation is:

sudo apt-get install remotepi