Blu-ray frame rates

Last night I received a question by email, and I thought I might as well deal with it here. David writes:

I’m a big fan of blu ray’s 24p mode, because it eliminates two bug-bears of DVD transfers from film; 3:2 pull down artefacts on NTSC (although I’ve never noticed them), and the wrong speed transfers of PAL (which bothers me just knowing about).

I was wondering if you could tell me which frame rate would be used for the Australian blu-ray issue of a TV series made for American TV.

Frame rates don’t seem to be listed in the features section on the back of blu-ray packaging, although I specifically selected my TV because it was compatible with 24p, when some cheaper ones don’t make that claim. I can only assume they won’t do work with that, and that’s the reason 24p is an option on my blu-ray player, in case you have a TV that won’t work with that. Please advise?

The great majority of movies released on Blu-ray have a frame rate of 1080p24, by which I mean that the frame rate is 23.976 frames per second (ie. 24/1.001). The reason for this slightly-under-24fps figure is murky, but related to the US TV system. This is a very slight slowdown from the rate used in the cinema, and should be practically indistinguishable.

Some other Blu-ray movies sold in Australia use a frame rate of precisely 24fps (I mark these as 1080p24* to distinguish them). These should be identical in run length and audio pitch to those in the cinema.

And some Blu-ray movies sold in Australia use the 1080i50 format: that is, HD interlaced at 50 fields per second.

With a good Blu-ray player doing the progressive scan conversion, the output becomes 1080p50, with each two adjacent frames identical to each other, so in effect it is 1080p25. The picture quality should be just as good as 1080p24, in this case, but you have the 4% movie speedup and audio pitch increase.

If a Blu-ray disc’s packing specifies the video as being 1080p, then that must mean either 1080p24 or 1080p24*. Other frame rates at 1080p are not supported by Blu-ray.

If it specifies 1080i, then it could be 1080i50 or 1080i60. I expect that most US content at 1080i would be 1080i60.

As for US TV shows released on Blu-ray, they tend to be mostly 1080p24 (eg. Band of Brothers,¬†Futurama, Pushing Daisies, Star Trek (The Original Series), Star Wars: The Clone Wars). The stuff that’s worth putting out on HD has generally been shot on film, or is recent enough for them to have anticipated HD home release. Even some non-US TV content — Thunderbirds from the UK, made in the mid-60s — gets the 24 fps treatment (1080p24* in this case).

I’ve got the precise frame rates recorded on my Blu-ray reviews and comparisons, and there are even more shown on the ‘NEW Unofficial Blu-ray Audio and Video Specifications Thread‘, to which I contribute, and in which I recommend anyone with a Blu-ray drive in their computer participate.

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