Client sent me an emailing saying: "I believe the video should have been interlaced before it was supplied to us. Interlaced footage is designed for web delivery; de-interlaced footage as seen here is only used for TV broadcast and DVDs."
The video was shot at 50i on a Canon XHA1 (PAL) in the UK then edited as standard ProRes 422, exported as self-contained Quicktime from FCP, then this was brought into MPEG Streamclip.
Using MPEG Streamclip I created a compressed MP4 with the following stream info:
Data Size: 89.98 MB
Bit Rate: 1.21 Mbps
Under the MPEG Streamclip heading 'Deselect for progressive movies' I had 'Interlaced Scaling' ticked (yes), 'Reinterlace Chroma' ticked (yes, greyed out) and 'Deinterlace Video' not* ticked (no). Field Dominance was set to Upper Field First.
The result of this is that the video looks jagged, as per the photo.
By ticking 'Deinterlace Video' (Interlaced Scaling and Reinterlace Chroma greyed out and ticked) the 'jagged edges' seem to go away, as per the comparison in the photo:
Your client has the information backwards. Computer screens all display video progressively. All video for the web or to be viewed on a computer should be deinterlaced, that is to say it should have a progressive frame draw.
Interlaced footage is relegated to broadcast TV. Interlacing was actually a trick developed by broadcasters to save bandwith.