Willen wrote:I think you meant to type 1080p30.
The reason the BD specs say 1080i60 and not 1080p30 is because if done properly, you can use that interlaced signal to store true 60i and 30p footage. If you are encoding native 1080i60 ATSC video you are golden. If you have 1080p footage shot at 30 frames per second, possibly from some AVCHD cameras or video-capable DSLRs, it would be stored as interlaced field pairs on the BDs (i.e. 1080p30 converted to 1080i60). It should be no different than how DVDs handle pure interlaced material derived from 30 (29.97) frames per second original footage. De-interlacing on playback should be pretty straightforward to reconstruct the original 30 frames.
As for if the footage is properly flagged as pure interlaced or field pairs for correct playback, I don't know...
BTW, most 1080i60 BDs I've encountered are of the National Geographic documentary type. Most of them are shot with HD video cameras which operate at 60i (NTSC/ATSC). I would imagine the expense of shooting in 35mm film (or even IMAX) would go above the budgets of most of the programs.
No, I meant 1080i30 - I default to referring to fps by the proper # of frames, no matter whether the method is interlaced or progressive. 30 frames per second, interlaced, rather than 60 fields per second, interlaced (in which case saying 'interlaced' is redundant). The European Broadcasting Union denotes it in a similar manner, 1080i/30 or 1080i/25 - I'm just too lazy to bother putting a slash in there like they do.
When you mention field pairs though, are you talking about [essentially] pulldown flagging (I assume not, considering you're talking about deinterlacing on playback)? Faking out a player by using the interlaced flag on progressive footage? I've seen talk of that on Doom9, but the general impression I got from there is that it's iffy whether all Blu-ray players support it, or whether it's simply an assumed trait.
The point being, that unlike DVD where you could have a progressive 29.97fps stream stored as Progressive, you're not allowed to do that on Blu-ray for whatever stupid reason (no matter what resolution you're talking about - 480, 720, 1080: all of them say i60, not p30). Sure, you can reconstruct 1080i into 1080p using TFM just like you can do with DVD footage, but 'reconstruct' and 'supports 30 fps progressive' are two different things. '30p' means it had better be stored progressive, no reconstruction necessary. Hence the flagging trick I mentioned earlier that doesn't seem to be spec-compliant even if the players accept it.