iPlayer deinterlacing snafu

The BBC’s iPlayer system manages to deliver remarkably high-quality video over the web, but it’s not flawless. Most of the problems I’ve seen, like this one, seem to revolve around interlaced video. Specifically, the way it’s deinterlaced.

This is a straightforward transcoding goof – the fields should have been deinterlaced to one set of frames, not… er… four – but I’ve also seen some pretty ghastly field inversion issues – where successive frames on iPlayer have ping-ponged back-and-forth, so that fast pans and tilts have stuttered terribly. Most notably, the high-res iPlayer version of one of Stephen Fry’s Last Chance to See programmes was unwatchable. Not merely ‘broadcast-wonk-turning-his-nose-up’ unwatchable, but ‘oh-hell-I-feel-ill’ unwatchable.

It’s not quite clear to me how this could be happening, in that you’d think the digital masters they’re working from would be in one of a small number of tightly-defined formats. Certainly, BBC technical review is extremely strict, as anyone who’s had a Kafkaesque argument with that department will confirm.

Also, it seems that there’s not much quality control on the finished transcode – or at least, not by anyone who recognises field issues when they see them. The Last Chance to See clip was fixed after a few days, but the programme of Bang Goes The Theory from which this frame is taken is still live, two months later (still is from around timecode 27.43).

Much as I hate to sound like Disgusted of Tynemouth, this is the sort of thing the BBC should get right, every time. They should be humbling the rest of us with their sheer technical prowess.

As it stands, oiks like me shoot everything we intend for the web with progressive frames and proper square pixels, edit and deliver via formats that retains those properties (ProRes and H.264, in my case), and thus never see any problems. It’s the national broadcaster who get tripped up by the details.