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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2 Responses to Blu-ray frame rates

  1. Craig says:

    “Underbelly” on blu-ray is 1080/50i, and no speed up has occurred due to this programme being filmed at 25/50i to begin with. So, at 50i (or (50p), you’re actually watching it at the original and correct frame rate/audio pitch.

    The filmed footage was captured at 25p on HD video, but the end title sequences and lower frame supers that animate are actually 50i, meaning they have 50 unique pictures per second. So the only correct way to view this programme is at 50i or 50p.

    Merging fields or frames down to 25p (or 24p) would be a travesty. The blu-ray producers knew this, so correctly authored the blu-ray at 50i. Well done.

    The same cannot be said for some BBC docos, which, even though they were mastered at 50i and contain 50Hz video sequences, have been ‘slowed down’ and ‘field-merged’ to 24p for the international market, and unfortunately we are stuck with this. They obviously didn’t have the budget to produce a separate 1080/50i version for PAL [Region B] territories.

    Craig.

  2. Stephen Dawson says:

    Yes, if Underbelly were ever to be marketed in the US, they’d have to do either a 24 or 60Hz conversion (both, probably, the first for Blu-ray and the second for DVD). Hopefully they’d simply re-render the credits rather than do some form of field merge.

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