4OD adding filmic effect to programmes

Sorry if this has been mentioned elsewhere, but can anyone explain the logic of Channel 4 removing frames from some of its programmes on 4OD? I'm currently watching Drop The Dead Donkey on Virgin and they've added the filmic effect. I've noticed they have started to do it to a lot of their programmes including Richard and Judy, which looks very odd.

I've said it once, i'll say it again... programmes that were not produced, lit etc to accomodate a filmic look should never me altered in this way.

I'm guessing that shows are being encoded in 25fps rather than 50fps, which I'm guessing is down to quality and size reasons (the lower the framerate, the better the quality at the same bitrate).

Does this also apply to the internet download version of 4OD, or only on the cable version?

I wouldn't be able to see a difference, as all 4oD programmes I watch online are compressed anyway.

4oD and BBC iPlayer stuff for download or streaming via the internet is all resolution reduced, to lower than field resolution (i.e. a UK SD interlaced TV frame is 720x576 made from two 720x288 fields), and a by product of this is that they don't send content as interlaced - and I suspect they just scale one field down rather than doing a decent de-interlace in the coder.

For film content this is fine, but for sport/news/entertainment etc. it means that the fluid motion of video is ditched and looks "filmic".;

It would be possible for them to de-interlace to 50fps and then resolution reduce - but the increase in frame rate would require more bandwith/larger file sizes.

I am disappointed that the 2 main download services don't offer a choice of file size - but I suspect they don't want us to get full DVD quality stuff via download - so we'll buy the DVDs...

I'm not familiar with the Virgin Media system. I suspect it is using re-encoded low-ish bitrate encodes of the shows so that they don't have to tax their servers too much when lots of people VOD at the sam time. I also don't know the format they use (MPEG2, H264 etc.) and it could even be they are running at something nearer Video CD quality MPEG1 (360x288 rather than 720x576). VCD MPEG1 only effectively carries one of the two fields of an interlaced frame at 25fps - so always gives video content a "film look"

Unusually I disagree with noggin on this one.

I think is is de-interlaced 720x576 (both fields) and not just one field. De-interlacing will give a 'film' effect anyway to an extent.

It is more noticable on old Channel 4 stuff in part becouse the video to start with is not the crispest - Drop the Dead Donkey on Paramount is a little a little 'analogue' and looks only marginally better than 80's Kenny Everett Shows.

I don't have any facts to back this up but I'd say it's better than VCD MPEG 1 - I consider myself to be reasonably picky and most of the stuff on VOD looks pretty good quality (although admittedly I don't have a large high-end TV).

I'm almost certain it's not de-interlaced.

The music videos are definately more compressed than the TV shows. I've noticed that with Virgin.

I wonder if the iPlayer on Virgin when it launches (supposedly next month) will have the full archive as I notice 4OD always has much less to catchup with than on the internet.

Depends on your de-interlacing algorithm. My comments about ditching one field were more to do with the 224ish line resolution iPlayer stuff online (i.e. download and Flash streaming) which are 25fps with no interlace and thus have "film" motion.

De-interlacing to 25p will give a film effect - and if running at below 288 line resolution (i.e. field resolution) then a quick and dirty way of doing this is to discard a field (though it can introduce aliasing on fine vertical detail the lower the resolution - the less of an issue this is)

De-interlacing to 50p won't give things a film effect - and can be done at sub 288 line resolution as well to deliver low resolution but full motion. However very few implementations in use do this.

(Even early PC DVD players at full res de-interlaced 50i to 25p - though most now include a proper de-interlacing algorithm that delivers 50p motion - which is what is required to watch 50i content with full motion on a progressive display - like a PC monitor. Even VLC defaults to no de-interlacing - and you have to be quite careful to select a mode that does a decent de-interlace to 50p)



Hmm - Drop the Dead Donkey was quite a lot better quality than the Kenny Everett stuff - but was shot using some kind of Superfrost-like diffusion filters to give it an intentionally less-harsh look. This was quite common on drama and sitcome in the late 80s and early 90s.

Of course without seeing the shows it is difficult to know whether the film effect has been applied as part of the compression for VOD - or as a separate artistic decision. I suspect the former - but without seeing them it is difficult to tell.

The normal BBC Real/Windows streaming tends to use either Digital Rapids or Viewcast cards. I've not used the Digital Rapids kit, but the proper way to set up a Viewcast Niagara or standalone Osprey card is to get the card driver to do a high quality hardware deinterlace and resize on the incoming signal, then present it to the encoding software already in the correct resolution - so all the encoder software has to do is encode.

You get a much better result this way than trying to get the encoding software to deinterlace and resize itself. This also saves CPU resources on the box if you are running multiple format encodes, as the drivers do the computationally expensive resize and deinterlace the once rather than multiple times in each encoding application.

What de-interlacing algorithms do they use to deliver "high quality" de-interlacing? Presumably they are de-interlacing to 25p not 50p (so describing them as high quality is a bit misleading as they are not utilising any motion above 25p?) Do they do a decent interpolated de-interlace using motion from both frames to create a new 25p sequence - or do they just take the motion from one frame (or field)?

Do they use motion adaption or motion compensation for the de-interlace ?



So the card digitises, de-interlaces and scales and delivers an uncompressed video signal that is then encoded into WMV, Flash, RealVideo etc. by the CPU from a common video source? (i.e. the 576/50i source is de-interlaced and scaled to 224/25p in the card but then the 224/25p video is compressed in different encoding applications?)

As usual the manual is a bit vague on the exact process, however one thing is does state is that a single field will be used ONLY if the output resolution is divisable by 4 or 2 from the input resolution. So 224x2=448 which is not 576 - so in this case both fields from the 50i source will be used.



It is motion adaptive and a test mode is provided in the drivers that colours the detected motion in green and allows you to play with the sensitivity. Defaults are usually correct though whenever I've had a look.



Exactly. In fact you can set up a number of different processed outputs from the board if you want to. They appear as different video boards to the software, so you could have a 400x224x25p product as board 1.1 for broadband and a 256x144x15p product on board 1.2 for narrowband if your machine had enough processing power to do 2 deinterlaces/resizes and 4 or 5 encodes - but had trouble with doing all 4 or 5 deinterlace/resize/encode steps at once.

One thing that also makes a big difference to quality is the incoming signal. I've seen the iPlayer servers in the Red Bee data centre, so they should be getting a nice uncompressed SDI signal direct from the playout suites above. Of course the signal has been compressed before, but hopefully nothing worse than DV. Likewise Arabic takes an SDI feed from Egton. However I have my suspicions that Siemens are not encoding the BBC Three stream from an uncompressed SDI source from the playout suite.