[noggin]

Thanks for the reply. To be honest I didn't even know companies were releasing VC-1 blurays with 1080i resolution.Seems an odd choice.

Not really. VC-1 and H264 offer broadly similar levels of compression, so unlike MPEG-2 (which is also a Blu-ray codec) there isn't a huge benefit of one codec over the other in quality terms, so that covers the codec choice. I think H264 is probably better supported in the mastering arena possibly, but if you have mastering tools that support VC-1 then there may be reasons to use it? However I get the feeling that more effort has gone into optimising H264 compression - but at the bitrates Blu ray supports this may be less of an issue than at the bitrates used for DVB broadcasting for instance.

As to the 1080i question - there are two reasons I can think of.

1. Your source material is 1080i native because you shot the material you are distributing 1080i. That would be the case for non-movie stuff like pop concerts, sporting events etc. The main feeds for the Winter and Summer Olympic Games, for instance, are shot 1080i natively by OBS (the host broadcaster). The reason for this is that concerts and sport benefit from the more than double image refresh rate that 1080/50i and 1080/59.94i offers compared to the 1080/23.976 or 24.000p formats that Blu ray supports. (This is why properly deinterlaced 1080i has much smoother motion than 1080/23.976p)

2. Your source material is 1080/25p (which is the standard format for drama and a lot of documentary in 50Hz TV territories). Blu-ray, for some stupid reason, doesn't allow for 1080/25p native mastering, and in many cases TV shows are mastered in 1080i (with the 25p content carried as psf - but with 50i motion on credit rolls and crawls) so European TV shows released on Blu-ray are often 1080i too (This isn't universal - some shows are slowed down to 1080/24p and released using 'PAL slowdown' with the music pitch corrected)