To be fair, quality is still affected to an extent when you're filmising a 50i master, which Call The Midwife still is, even if the content was shot at 25p (25PsF I believe is the proper term for 25p material in a 50i wrapper). It's still effectively cutting the resolution down from 1080 to 540 unless they're explicitly not de-interlacing the footage and showing both fields at the same time. So the 1080p version of Call The Midwife on Britbox could be lower quality than the 720p version on iPlayer depending on how they've handled the interlacing.
Nope - any decent deinterlacer will take 1080i25 masters containing 1080psf content and deliver significantly better resolution than 540p, and that also ignores the 1920 vs 1280 horizontal resolution difference between 1920x1080p and 1280x720p.
Only a really terrible bob deinterlacer will take 1080i25 and constantly deliver 540p equivalent resolution. Anything that does any form of motion detection, motion adaption, motion compensation or uses a decent vertical/temporal filter approach (i.e. any modern deinterlacer that anyone would actually use) will deliver >540p equivalent resolutio on psf content with no intra-frame motion. (1080i25 masters with 1080p25 content in them MAY have a degree of vertical pre-filtering to reduce interline twitter - but this is likely to be relatively mild, and still leave a reasonable amount of >540 line vertical resolution)
Heck even native interlaced content will deinterlace to better than 540p with any modern, decent, deinterlacer on static and slow moving elements)
1080i25 content containing 1080p25 acquired video, deinterlaced properly to 1080p50, looks a lot better than the same content deinterlaced and downscaled to 720p50.
If you are taking 1080i25 to 1080p25 - then again a decent deinterlacer will do a lot more than just discard source fields - though taking 1080i25 (whether p25 or p50/i25 native acquired) to p25 is not a great approach across the board - which is why a lot of us have issues with BritBox running at p25 not p50. iPlayer switched from p25 to p50 quite a few years ago for good reason - as have many other catch-up and OTT platforms (ARD and ZDF Mediathek in Germany, lots of the OTT pay platforms like CMore, Telia Play etc, in Scandinavia, even NowTV for sport)
Last edited by noggin on 8 January 2020 10:18am - 3 times in total