31 January 2011

Filming with an iPod

The latest versions of Apple's omnipresent mobile phone, iPhone 4, and its slightly-less featured sibling, iPod Touch 4, have raised a few eyebrows with their ability to shoot HD video.  When given the opportunity to buy one of these iPods on the cheap, I was curious as to how good the footage would turn out, and these are my first impressions from a film-making point of view.

In case you're not familiar...
The iPhone 4 and iPod Touch 4 are slim devices the size of a regular mobile phone, albeit with the entire front face as a touch screen, and only a couple of other buttons around the edges.  The device is very light and can generally be carried around even in the tightest of tight-fitting jeans pockets.  I imagine.

Touching up
Handling the thing is tricky.  At first I held the iPod in my thumb and forefingers at the corners, and soon found a murky, vaguely finger-shaped shadow in the picture; the lens is situated in one corner on the back of the casing and easily picks up a clumsily-placed digit.  Eventually I found the best way was to hold the iPod like a judge at a ballroom dancing competition would hold a numbered card reading '6.0'.  So I understand.

Video format
The two devices have very similar video shooting capabilities, and as mentioned above, they shoot HD.  It's not Full HD though, just 720p (or 1280x720 resolution in progressive scan, if you're not a fan of abbreviating in general).  Still, not bad for a glorified telephone or glorified Walkman.  This particular feature was what originally interested me in the film making possibilities, partly due to YouTube et al now showing video in 720p format (and lately in 1080p too), and partly because my most capable video camera is an old standard-definition MiniDV example.
(Indeed, the iPhone/iPod Touch even gives you the option of uploading your freshly-shot video direct to YouTube or send by email, before any editing has been made or audio added, which makes me shudder a little.  Apple thoughtfully provides a special version of the iMovie application for editing on the device itself, which you can buy for a few pounds.)
The video codec is H.264, familiar to anyone filming on solid-state camcorders or video-enabled SLR cameras.  Putting the footage into a traditional editing workflow, such as with Final Cut Pro or Adobe Premiere, entails some jiggery-pokery before computer-based editing can begin in earnest.  The iPod's video bit rate is around 10-11 Mbits/sec, quite a bit less than the 30-35 Mbits/sec recorded by a proper camera.  A lower bit rate means less data in the video file, but the file is smaller and takes up less space on your memory card or hard disk.

Frame rate foolishness
I was concerned by only one feature of the iPhone/iPod's video recording capability, when I read reports of a variable frame rate.  The software adjusts the FPS to a figure somewhere between 24 and 30, purely to control exposure.  The frame rate is established when shooting starts, and that rate is maintained to the end of shooting the clip, no matter how light changes in the scene; if you happen to start shooting in a bright, well-lit area and move along to a darker composition, the frame rate will not adjust to compensate, but noise appears in abundance.

1:1 crop of a video frame under domestic lights, click to
view at full size to appreciate the sheer noisyness.

The FPS figure can be rather arbitrary; recently I shot a clip at the rate of 26.73 frames per second.  A video editor baulks at the thought of arranging a number of clips with different frame rates on the same timeline.  As far as I can see, there is no indication on the device what kind of random assortment of numbers it has decided to bestow on the frame rate, so you have to wait until you transfer the file to a computer, open in QuickTime and check out the properties (as per the screen grab below).

Movie properties from within QuickTime.

It's not all bad
If the above sounds like a tirade of cynicism, that's because it is.  However, more professionally-minded folks have squeezed some impressive performance our of these little gadgets, the most well-known and earliest example (it was filmed a few days after the iPhone 4 was launched, and edited the following day using iMovie on the phone itself) is Apple of My Eye by Michael Koerbel:

Apple of My Eye from Michael Koerbel on Vimeo.

More to come
I'll have more feedback about my experimentation with iPod video in the coming weeks.