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Caktus Ship It! Day 2014 Q3 Post-Mortem - Part 2: Playlists and Peers

As of my first hour playing around I was able to share and synchronize play of any MP3 between multiple users with a simple drag and drop interface. Things were going pretty well for my project, but I had some work to do getting from there to the collaborative playlist I had in mind.

I was already just assuming we were only caring about one file, because that worked well to get things up and running fast. My next step was to remove that assumption and start keeping a list of songs. This was pretty easy, in fact. I started writing a simple list of songs as they were downloaded, each with a play button which performed the <audio> tag set and play that previously done automatically. Each user could now play any song that was shared and to restore the previous synchronized playing that happened when they only dealt with a single done I incorporated broadcast changeTrack messages. I added two other broadcasts, pause and play, which would allow any users to pause and play the songs on all users simultaneously.

This was working well, and I had roughly scaled my previous prototype to a multi-song version. Unfortunately, this version was even more rough and bug-ridden than the first. Most importantly among its faults: I couldn't really predict the order different clients would receive each track, so the playlists wouldn't remain in the same order for everyone. I wasn't really ready to tackle the actual collaborative playlist problem. This is probably the most difficult problem the project will face. It is a lot harder because I'm determined to keep the entire thing peer-controlled with no central decided or coordinator.

After banging my head on the simplest way I could provide this editing for the initial version, but coming up short, I realized it was a waste of my time. I didn't really need to do collaborative editing for a prototype, I just needed to make sure they all kept the same order.

So I alphabetized the songs for all users.

The simplest solution to some problems is not to have them

At this stage I could play any song on the shared playlist and hear it on any connected machine. Things continued nicely.

Implementing playlist progression was pretty easier. Along with progression I added highlights on the list to show which song was currently being played.

I decided at this point to do a bit more seriously testing and increased my test set of songs I was drag and dropping from 3 to 8.

I crashed Chrome. How I did that and how much of this work I had to completely throw out the window? Read Part 3 (Coming Soon) to find out.

Part 1: Proof of Concept in Under an Hour

Part 2: Playlists and Reseeding Songs

Part 3: Two Steps Back and Three Steps Forward

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