UHD Capacity Question

[Shane Rollins]

Basically, how much can a UHD disc hold? Preferably in terms of hours.

We know that a BD-50 can hold 8 hours of HD content or 23 hours of SD content, and a BD-25 can hold roughly half of that. How much can a BD-66 and a BD-100 hold? How much 2K content and how much 4K content? How does SDR/HDR/DV etc factor into it, and how much do they reduce the capacity of the disc? (So I guess how much in SDR, how much in HDR, how much in DV, etc?) The answers I find online are either stupid answers ("a BD-100 holds 100 gigs") or they have so much jargon that I can't make sense of it.

[Telemachus]

a BD-100 holds 100 gigs

[apollo828]

Long story short, you're just going to have to make sense of the jargon. Capacity simply depends on the disc size (50/66/100) and number of layers. From there, the maximum read rate depends on both factors. Next, bitrate just depends on encoding. HDR is applied on top of SDR, so it does add bytes, but how many bytes depends on encoding. (Some discs, like The Last Jedi, are technically DV but really just add a "wrapper" that's approx. 80 MB and does nothing to the actual image. Remove DV, and the image doesn't change one bit.) So, it all depends.

With all that said, if you used a triple-layer disc, used 24 fps material (i.e., not HFR), maxed out the transfer rate the entire time, and only had one audio track for the video, you'd get approx. 5.5 hours of material. A BD66 would be approx. 4.25 hrs, and a BD50 would be approx. 4 hrs. The real numbers might be a bit higher but I'd have to go diving deep into the specs for precise numbers. This will get you in the ballpark.

[Naiera]

Originally Posted by Shane Rollins

Basically, how much can a UHD disc hold? Preferably in terms of hours.

We know that a BD-50 can hold 8 hours of HD content or 23 hours of SD content ...

Where'd you get those numbers? They're data discs. Minimise the bitrate enough and they'll hold days of footage.

[BijouMan]

Originally Posted by apollo828

Long story short, you're just going to have to make sense of the jargon. Capacity simply depends on the disc size (50/66/100) and number of layers. From there, the maximum read rate depends on both factors. Next, bitrate just depends on encoding. HDR is applied on top of SDR, so it does add bytes, but how many bytes depends on encoding. (Some discs, like The Last Jedi, are technically DV but really just add a "wrapper" that's approx. 80 MB and does nothing to the actual image. Remove DV, and the image doesn't change one bit.) So, it all depends.

With all that said, if you used a triple-layer disc, used 24 fps material (i.e., not HFR), maxed out the transfer rate the entire time, and only had one audio track for the video, you'd get approx. 5.5 hours of material. A BD66 would be approx. 4.25 hrs, and a BD50 would be approx. 4 hrs. The real numbers might be a bit higher but I'd have to go diving deep into the specs for precise numbers. This will get you in the ballpark.

BDInfo scans show that there are many films less than three hours that fill up entire BD-100 discs. Remember that while Blu-ray maxes out at 54 Mbps, Ultra HD Blu-ray maxes out at 144 Mbps.

[apollo828]

Originally Posted by BijouMan

BDInfo scans show that there are many films less than three hours that fill up entire BD-100 discs. Remember that while Blu-ray maxes out at 54 Mbps, Ultra HD Blu-ray maxes out at 144 Mbps.

So, it does look like I goofed on some numbers. Thanks for double checking.

- The raw amount of available data on a BD100 is 100,103,356,416 bytes. However, due to error correction code, this is reduced immediately to 96,882,130,944. You lose over 3 GB simply ensuring that the data you read is correct.
- The maximum transfer rate for a BD100 is 144 Mb/s, or 18,000,000 bytes/s. (I don't know the precise max bits for audio/video/subs/etc. offhand.) Assuming you could somehow use every byte for a movie (and you can't), that's roughly 1h29m42s.

In practice, no movie does this. That and some may use the default 123 Mb/s profile, which bumps everything to 1h45m01s. Very roughly speaking (I don't know the precise BD66 numbers offhand), a BD66 would max out at 1h10m01s. (BD66 can't use the high TR option and maxes out at 123 Mb/s.)

(Also, for the sake of completeness, a BD50 tops out at 50,050,629,632 bytes. At 92 Mb/s - the max for UHD BD50 - you get 1h12m32s.)

Either way, there's also overhead to consider.

- You lose some space due to various bits of overhead related to the BD spec. In particular, the MPEG transport stream adds 1+ GB of data to a movie. You can strip that data and still have a playable movie, but the data's needed as part of the spec.
- If you make like Sony and have 20+ audio streams for a movie, those streams require space. That really eats into the video bitrate.
- Atmos and DTS:X soundtracks eat up a lot of space. Even a single DTS-HD MA or TrueHD 5.1 or 7.1 soundtrack will still eat up several GB of space.

So, going back to the original question, it simply depends. Compression is everything, which is why one should compress as much as possible without introducing artifacts. Some people are much better at it than others.

[David M]

Originally Posted by Shane Rollins

Basically, how much can a UHD disc hold? Preferably in terms of hours.

It depends on the amount of high frequency content (sharp fine details) and motion in the video. Plus the quality of the encoder used.

In terms of UHD BD and 100gb discs: you could fit 35+ hours of talking head video interviews on a 100gb disc with HEVC provided it wasn't too noisy (or had been NR'd).

On the other hand, for content with sharp film grain where you need to preserve that by maxxing out the video bitrate if possible, a 100gb disc could hold a little over 2 hours.

If you don't mind lowpassing the video (removing the tiniest details, which the codecs do a bit of by their very workings anyway) and accepting slightly lower quality, you could fit a lot more.

The question is quite subjective because the loss of high frequency components is gradual.