Resizing BluRay Discs

[ChrisR34000]

Hi!

Why do most of the people resize a bluray disc to a smaller resolution when they encode? Why not encode a bluray disc to 2,1 GB and keep it at 1080p? I didn't really notice a quality loss when keeping the original resolution. Thanks in advance for your time.

Chris

[Blue_MiSfit]

...

Why 2.1GB?

Most folks around here either encode to DVD5 / DVD9, or use CRF mode and don't care about filesize (as long is it's significantly smaller than the source).

Sometimes (if you're bent on DVD5, or want some smaller size), it ends up looking better to encode at 720p or some smaller resolution.

Not everyone has the same eyes, or the same display - for that matter :)

~MiSfit

[ChrisR34000]

...


Sometimes (if you're bent on DVD5, or want some smaller size), it ends up looking better to encode at 720p or some smaller resolution.

~MiSfit

Why? Can you present me the technical background regarding this?

[Adub]

Because if you encode two streams, one 1080, the other 720, at the same bitrate, to reach the same file size, the 720 file will be much higher quality.

The reason is because of the resolution. With 1080, there are 1920x1080 pixels to encode. With 720p, there are 1280x720 pixels to encode. Less pixels with the same bitrate = more bits per pixel => higher quality. Besides, most people can't tell the difference between 1080 and 720, or atleast not enough to care.

For them, it's just High Definition that looks good in a small file size.

[Sagekilla]

It depends on if you do prefiltering too. I can get my rips down to 2 GB easily with a 448 kbps AC3 track, like Superbad which I have at 1.8 GB for 720p. If I chose to do 1080p I might have been able to get this in 3 GB easily.

[ChrisR34000]

It depends on if you do prefiltering too.

In what way?

[Sagekilla]

Like using MVDegrain to remove noise and grain. I do this for every movie I rip, and I've gotten massive reductions in file sizes.

[ChrisR34000]

Like using MVDegrain to remove noise and grain. I do this for every movie I rip, and I've gotten massive reductions in file sizes.

Does MVDegrain a good job generally?

[Sagekilla]

Generally it does, I've yet to encounter any artifacting with MVDegrain using proper settings (overlap=2 at the VERY minimum.) I only use MVDegrain because a lot of the filtering scripts out there now are far too slow to work with Blu-ray movies. Besides, Blu-ray tends to be such a clean source you don't run into issues of noise and artifacts introduced from insufficient bitrate, so there's much less of a need to do extreme filtering for good results.


Example: Superbad (http://www.mediafire.com/download.php?116kj8uhmtb) that I was just talking about. I'll cut out 30 seconds from the movie so you can see the quality. I had it encoded @ CRF 19 and the only filtering done was with MVDegrain3. But I digress, the point is that you don't really need the 50% extra resolution. The extra bits required for that many more pixels is simply not worth it.

[ChrisR34000]

Thanks alot Sagekilla! How much slower is the encoding process with filtering compared to no filtering with MVDegrain?

[Sagekilla]

Exceedingly slow.. We're going a bit off topic here, but I tend to use blksize=8, overlap=2, pel=2 on MVAnalyse and use MVDegrain3. If we're talking about watching the movie only, I get barely over 2-5 fps in mpc. Remove MVDegrain and I can do well over 30 fps easily. This is also with the latest version of MVTools which supports multithreading.

If you're not decoding Blu-ray movies, it becomes less of a hassle to filter.

[foxyshadis]

About the original topic, the #1 reason is speed. Everything done in 1080p takes more than twice as long, since there's more than twice the pixels to work with: deinterlacing, denoising, encoding. Playback only takes about 10-15% more at the same bitrate. Then, as mentioned, 720p is already 3 times the pixels of a DVD, having twice as many again isn't as big of a leap.

At the original resolution, you may not notice a quality loss at the same bitrate, but do you notice a quality gain? If not, then there's no reason to bother spending more than twice the time on the rip. You can only store so much in a given bitrate, some tradeoffs have to be made, the 1080p will always have more artifacts but they may not outweigh the resolution gain, that's up to you.

[fib0by]

1080p compressed to fit on a DVD9 (dual-layer DVD) always looks good enough to me. A 90 min movie looks excellent. 120 min looks still very good, no artifacts visible from the normal viewing distance. I'm not sure what happens with a 180 min movie, I have yet to try that, but my guess is - it can't be bad.
Modern CG animation always looks better, since the source is clean. Grainy movies look less good, because grain is noise and means additional stress for the encoder. But I never had to de-grain a movie yet. Maybe I'll do that if I have to fit 3 hours of grainy movie on a DVD9.

All this with x264 2-pass, MeGUI with the Standalone-AVC-HD preset from Sharktooth's list of presets. Only one audio track preserved (usually a 5.1 AC3 track) and one subtitles track.

http://forum.doom9.org/showthread.php?t=139765

I calculate the bitrate so as to fill 8150 MB almost completely.

Bitrate = 0.95 * (8150 - AudioSize - SubtitleSize) * 8 * 1024 / MovieDuration

Sizes are all in MBytes. Duration is in seconds. Bitrate is in kbits/s
0.95 is there to account for encapsulation, encoder overshooting, etc.
I have a small bash script that I run in Cygwin that does all this for me. Previously I tried RipBot but it has too many issues (uses a Blu-Ray preset instead of AVCHD, does not want to use .sup subtitles, etc.)

You need a fast CPU. An AMD64 x2 5200 was too slow for me. With a Phenom x4 9850 I can start the encoding in the morning and it's done when I get back home in the evening - no more overnight encoding. x264 scales very well with the number of cores, so a quad core is an advantage.

My goal is not "perfect" encoding, but only "good enough". So far, DVD9 and 1080p together were able to meet this goal.
DVD5 is too small for HD. You either start to get artifacts, or have to scale down to 720p. Neither is acceptable to me.