TheyWorkForYou video timestamping has been launched, over 40% of available speeches have already been timestamped, and (hopefully) all major bugs have been fixed, so I can now take a short breather and write this short series of more technical posts, looking at how the front end bits I wrote work and hang together.
Let’s start with the most obvious feature of video timestamping – the video player itself. mySociety is an open-source shop, so it was great to discover that (nearly all of) Adobe Flex is available under the Mozilla Public Licence. This meant I could simply download the compiler and libraries, write some code and compile it into a working SWF Flash file without any worries (and you can do the same!).
To put a video component in the player is no harder than including an <mx:VideoDisplay> element – set the source of that, and you have yourself a video player, no worrying about stream type, bandwidth detection, or anything else. You can then use a very useful feature called data binding to make lots of things trivial – for example, I simply set the value of a horizontal slider to be the current playing time of the video, and the slider is then automatically in the right place at all times. On the downside, VideoDisplay does appear to have a number of minor bugs (the most obvious one being where seeking can cause the video to become unresponsive and you have to refresh the page; it’s more than possible it’s a bug in my code, of course, but there are a couple of related bugs in Adobe’s bug tracker).
As well as the buttons, sliders and the video itself, the current MXML contains two fades (one to fade in the hover controls, one to fade them out), one time formatter (to format the display of the running time and duration), and three web services (to submit a timestamp result, delete a mistaken timestamp, and fetch an array of all existing timestamps for the current debate). These are all called from various places within the ActionScript when certain events happen (e.g. the Now button or the Oops button is clicked).
Compiling is a simple matter of running mxmlc on the mxml file, and out pops a SWF file. It’s all straightforward, although a bit awkward at first working again with a strongly-typed, compiled language after a long time with less strict ones The documentation is good, but it can be hard to find – googling for [flex3 VideoDisplay] and the like has been quite common over the past few weeks.
Tomorrow I will talk about moving around within the videos and some bugs thrown up there, and then how the front end communicates with the video in order to highlight the currently playing speech – for example, have a look at last week’s Prime Minister’s Questions.