GiP-2.95-develop & list archives

[John Warburton]

On Thu, Apr 7, 2016 at 8:11 PM, Paul Phillips <
paulphillipsdidsbury at gmail.com> wrote:

> it was
> posted previously in the Support Forum
> that the vast plethora of TV content on iplayer
> is not 50FPS originally, so for most 50FPS files
> there is a simple dublication of 25FPS=>50FPS,
> IOW in a minute's worth of video stream, there
> exist only 25 unique different frames.
> One notable exception to the above are sports
> events (and possibly other genres where quick
> motion is involved...).

I suggest that the 50fps modes are, in fact, the BBC's way of showing
equivalent interlaced movement via a progressive stream. Remember that
interlacing is a form of temporal compression. What's happening is that the
programme that began as 50 half-frames (i.e. fields) is now being sent as
50 full frames per second, with interpolation being used to create the
missing lines.

All BBC programmes (indeed, all UK programmes to broadcasters ascribing to
the Digital Production Partnership's standards) must be delivered as 25fps,
interlaced. Even if a programme is shot using cameras set to progressive
scan (for 'film effect'), it is important that the programme is delivered
interlaced because digital video effects and end-credit rolls and crawls
must move smoothly on viewers' displays. The specification is very clear
about this.

So the 50fps feeds give you the closest approach to what is seen in the
playout suites. But, yes, they are double the bandwidth and, for
progressively-shot programmes, you'll lose only the smooth motion of
credits and video effects if you download the 25fps version.
J