Tags: hack

I documented a weird bug with web audio on iOS a while back:

On some pages of The Session, as well as the audio player for tunes (using the Web Audio API) there are also embedded YouTube videos (using the video element). Press play on the audio player; no sound. Press play on the YouTube video; you get sound. Now go back to the audio player and suddenly you do get sound!

It’s almost like playing a video or audio element “kicks” the browser into realising it should be playing the sound from the Web Audio API too.

This was happening on iOS devices set to mute, but I was also getting reports of it happening on devices with the sound on. But it’s that annoyingly intermittent kind of bug that’s really hard to reproduce consistently. Sometimes the sound doesn’t play. Sometimes it does.

I found a workaround but it was really hacky. By playing a one-second long silent mp3 file using audio, you could “kick” the sound into behaving. Then you can use the Web Audio API and it would play consistently.

Well, that’s all changed with the latest release of Mobile Safari. Now what happens is that the Web Audio stuff plays …for one second. And then stops.

I removed the hacky workaround and the Web Audio API started behaving itself again …but your device can’t be set to silent.

The good news is that the Web Audio behaviour seems to be consistent now. It only plays if the device isn’t muted. This restriction doesn’t apply to video and audio elements; they will still play even if your device is set to silent.

This descrepancy between the two different ways of playing audio is kind of odd, but at least now the Web Audio behaviour is predictable.

You can hear the Web Audio API in action by going to any tune on The Session and pressing the “play audio” button.

I told you about how I’m using the Web Audio API on The Session to generate synthesised audio of each tune setting. I also said:

Except for some weirdness on iOS that I had to fix.

Here’s that weirdness…

Let me start by saying that this isn’t anything to do with requiring a user interaction (the Web Audio API insists on some kind of user interaction to prevent developers from having auto-playing sound on websites). All of my code related to the Web Audio API is inside a click event handler. This is a different kind of weirdness.

First of all, I noticed that if you pressed play on the audio player when your iOS device is on mute, then you don’t hear any audio. Seems logical, right? Except if using the same device, still set to mute, you press play on a video or audio element, the sound plays just fine. You can confirm this by going to Huffduffer and pressing play on any of the audio elements there, even when your iOS device is set on mute.

So it seems that iOS has different criteria for the Web Audio API than it does for audio or video. Except it isn’t quite that straightforward.

On some pages of The Session, as well as the audio player for tunes (using the Web Audio API) there are also embedded YouTube videos (using the video element). Press play on the audio player; no sound. Press play on the YouTube video; you get sound. Now go back to the audio player and suddenly you do get sound!

It’s almost like playing a video or audio element “kicks” the browser into realising it should be playing the sound from the Web Audio API too.

This was happening on iOS devices set to mute, but I was also getting reports of it happening on devices with the sound on. But it’s that annoyingly intermittent kind of bug that’s really hard to reproduce consistently. Sometimes the sound doesn’t play. Sometimes it does.

Following my theory that the browser needs a “kick” to get into the right frame of mind for the Web Audio API, I resorted to a messy little hack.

In the event handler for the audio player, I generate the “kick” by playing a second of silence using the JavaScript equivalent of the audio element:

var audio = new Audio('1-second-of-silence.mp3');
audio.play();

I’m not proud of that. It’s so hacky that I’ve even wrapped the code in some user-agent sniffing on the server, and I never do user-agent sniffing!

Still, if you ever find yourself getting weird but inconsistent behaviour on iOS using the Web Audio API, this nasty little hack could help.

Update: Time to remove this workaround. Mobile Safari has been updated.

I spent the last couple of weekends rolling out a new feature on The Session. It involves playing audio in a web page. No big deal these days, right? But the history involves some old file formats…

The first venerable format is ABC notation. File extension: .abc, mime type: text/vnd.abc. It’s an ingenious text format for musical notation using ASCII. The metadata of the piece of music is defined in JSON-like key/value pairs. Then the contents are encoded with letters: A, B, C, etc. Uppercase and lowercase denote different octaves. Numbers can be used for note lengths.

The format was created by Chris Walshaw in 1997 when dial-up was the norm. With ABC, people were able to swap tunes on email lists or bulletin boards without transferring weighty image or sound files. If you had ABC software on your computer, you could convert that lightweight text file into sheet music …or audio.

That brings me to the second old format: midi files. File extension: .mid, mime-type: audio/midi. Like ABC, it’s a lightweight format for encoding the instructions for music instead of the music itself.

Think of it like SVG: instead of storing the final pixels of an image, SVG stores the instructions for drawing the image instead. The instructions in a midi file are like “play this note for this long on this instrument.” Again, as with ABC, you need some software to turn the instructions into sound.

There was a time when lots of software could play midi files. Quicktime on the Mac, for example. You could even embed midi files in web pages. I mean literally embed them …with the embed element. No Geocities page was complete without an autoplaying midi file.

On The Session, people submit tunes in ABC format. Then, using the amazing ABCJS JavaScript library, the ABC is turned into SVG on the fly! For years I’ve also offered midi files, generated on the server from the ABC notation.

But times have changed. These days it’s hard to find software that plays midi files. Quicktime doesn’t do it anymore. And you’d need to go to the app store on iOS to find a midi file player. It’s time to phase out the midi files on The Session.

I still want to provide automatically-generated audio though. Fortunately ABCJS gives me a way to do this. But instead of using the old technology of midi files, it uses a more modern browser feature: the Web Audio API.

The end result sounds like a midi file, but the underlying technique is more like a synthesiser. There’s a separate mp3 file for each note. The JavaScript figures out how long each “sample” needs to be played for, strings them all together, and outputs them with Web Audio. So you’ve got cutting-edge browser technology recreating a much older file format. Paul Rosen—the creator of ABCJS—has a presentation explaining how it all works under the hood.

Not only is there a separate short mp3 file for each note in seven octaves, but if you want the sound of a different instrument, you need samples for all seven octaves in that instrument. They’re called soundfonts.

Paul provides soundfonts for ABCJS. It’s a repo that was forked from this repo from Benjamin Gleitzman. And here’s where it gets small worldy…

The reason why Benjamin has a repo of soundfonts is because he needed to create midi-like audio in the browser. He wanted to do this for a project on September 28th and 29th, 2013 …at Science Hack Day San Francisco!

I was there too—working on my own audio-related hack—and I remember the excellent (and winning) hack that Benjamin worked on. It was called Symphony of Satellites and it’s still online along with the promo video. Here’s Benjamin’s post-hackday write-up from seven years ago.

It’s rare that the worlds of the web and Irish music cross over. When I got to meet Paul—creator of ABCJS—at a web conference a couple of years ago it kind of blew my mind. Last weekend when I set out to dabble with a feature on The Session, I certainly didn’t expect to stumble on a connection to Science Hack Day! (Aside: the first Science Hack Day was ten years ago—yowzers!)

Anyway, I was able to get that audio playback working on The Session. Except for some weirdness on iOS that I had to fix. But that’s a hack for another day.

Your weekends are valuable. Spend them wisely. I have some suggestion on how you might spend next weekend, October 19th and 20th, depending on where you are in the world.

If you’re in the bay area, or anywhere near San Francisco, I highly recommend that you go to Science Hack Day—two days of science, hacking, and fun. This will be the last one in San Francisco so don’t miss your chance.

If you’re in the south of England, or anywhere near Brighton, come along to Indie Web Camp. Saturday will feature discussions on owning your data. Sunday will be a day of doing. I’ve written about previous Indie Web Camps before, and I really can’t recommend it highly enough!

Do me a favour and register for a spot—it’s free—so I’ve got some idea of numbers. Looking forward to seeing you there!

Last week was a bit of an event whirlwind. In the space of seven days I was at Indie Web Camp, Beyond Tellerrand, and Accessibility Club in Düsseldorf, followed by a train ride to Utrecht for Frontend United. Phew!

Indie Web Camp Düsseldorf was—as always—excellent. Once again, Sipgate generously gave us the use of their lovely, lovely space for the weekend. We had one day of really thought-provoking discussions, followed by a day of heads-down hacking and making.

I decided it was time for me to finally own my replies. For a while now, I’ve been posting notes on my own site and syndicating to Twitter. But whenever I replied to someone else’s tweet, I did from Twitter. I wanted to change that.

From a coding point of view, it wasn’t all that tricky. The real challenges were to do with the interface. I needed to add another field for the URL I’m replying to …but I didn’t want my nice and minimal posting interface to get too cluttered. I ended up putting the new form field inside a details element with a summary of “Reply to” so that the form field would be hidden by default, and toggled open by hitting that “Reply to” text:

<details>
    <summary>
        <label for="replyto">Reply to</label>
    </summary>
    <input type="url" id="replyto" name="replyto">
</details>

I sent my first test reply to a post on Aaron’s website. Aaron was sitting next to me at the time.

Once that was all working, I sent my first reply to a tweet. It was a response to a tweet from Tantek. Tantek was also sitting next to me at the time.

I spent most of the day getting that Twitter syndication to work. I had something to demo, but I foolishly decided to risk it all by attempting to create a bookmarklet so that I could post directly from a tweet page (instead of hopping back to my own site in a different tab). By canabalising the existing bookmarklet I use for posting links, I just about managed to get it working in time for the end of day demos.

So I’m owning my replies now. At the moment, they show up in my home page feed just like any other notes I post. I’m not sure if I’ll keep it that way. They don’t make much sense out of context.

Then again, I kind of like how wonderfully random and out-of-context they look. You can browse through all my replies so far.

I’m glad I got this set up. Now when Andy posts stuff on Twitter, I’m custodian of my responses:

@AndyBudd: Who are your current “Design Heroes”?

adactio.com: I would say Falcor from Neverending Story, the big flying dog.