Quality of BD50 to BD25 then BD25 to CRF ?

[Nico8583]

Hi,
I have made about 220 movies backups with BD Rebuilder from BD50 to BD25 (profil slower, 1 audio track and movie only) but now I would like to convert them to MKV CRF (between 20 and 23).
I would like to know if there is a big quality difference if I use BD25 source instead of BD50 ? I have all BD25 on my NAS so I don't need to rip original if I can use BD25.
Thanks for your advises !

[LoRd_MuldeR]

Why not simply remux your existing BD25 rips to MKV without re-encoding at all?

[Rumbah]

Well, in my experience you get much smaller files than 25GB for a movie even with crf 20.

I always use crf 20 preset veryslow level 4.1 and get about 5-10GB per movie file, subtitles and audio included.

[Nico8583]

@LoRd_MuldeR : Because I would like to reduce file size to store files on a little NAS

@Rumbah : Interesting point, do you see any difference between BD50 and CRF20 ? You keep 1080p or you resize to 720p ? And I suppose you don't keep HD audio ?

But I'm afraid to see a big difference between BD50 -> MKV and BD25 -> MKV :/

[Sharc]

I would assume that the bigger quality loss comes from encoding with CRF 20....23 which will mask the difference between the original BD50 or the BD25 backup as source for the re-encoding.

[benwaggoner]

You could also make your BD-25 discs with CRF 20 in the first place.

[Nico8583]

@sharc : it would be great ;-)
@benwaggoner : if CRF20 looks good for me, perhaps I'll stop to make BD25. But first thing is to know quality loss from BD25 :-/

[LoRd_MuldeR]

Originally Posted by Nico8583

if CRF20 looks good for me, perhaps I'll stop to make BD25. But first thing is to know quality loss from BD25 :-/

I'd agree with Sharc: If the CRF=20 encode comes out at about half the average bitrate (file size) of the BD25 encode, then you probably won't notice the difference between the BD25 and the BD50 source.

But only with some testing you will know for sure

[Rumbah]

I don't see any difference between the BD50 and the CRF20 encode on my TV. That's why I keep it that way.

I always use 1080p. I think you wouldn't see any difference between a BD25 to CRF20 as with most BD50 releases the movie itself isn't bigger than 25GB. But the only way to judge the quality is to just test it with your eyes.

For the audio part I use 448 ac3 5.1 as my Pi can play it without a problem and it sounds good to me. And most amplifiers take the direct spdif stream.

[Video Dude]

Originally Posted by Nico8583

Hi,
I have made about 220 movies backups with BD Rebuilder from BD50 to BD25 (profil slower, 1 audio track and movie only) but now I would like to convert them to MKV CRF (between 20 and 23).
I would like to know if there is a big quality difference if I use BD25 source instead of BD50 ? I have all BD25 on my NAS so I don't need to rip original if I can use BD25.
Thanks for your advises !

Since you did movie only with only one audio track, there is a good possibility that not all movies were recompressed in BD-RB as they could already fit on the BD-25. It is the menus, extras, and additional audio tracks that push it over to BD-50 many times.

Before re-ripping your collection, take a look at the file sizes and look for discs smaller than typical BD-RB x264 compressed target size. This would indicate BD-RB only remuxed the video and the video stream would match 1:1 with the source. This will save you time and effort of re-ripping those discs.

[benwaggoner]

Note you can make BD-25 compatible bitstreams WITH CRF. The -vbv-bufsize etcetera will still apply and keep things compliant.

For BD-25 and CRF 20, I'd recommend going down to a 25 Mbps peak and Level 4.0, which allows you to turn --slices 4 off. If you go down to a 15 Mbps peak, you can also use a 2 sec max GOP instead of 1 sec, and that might be just fine with CRF 20 and high-quality encoding settings.

[Nico8583]

Thanks to all for your responses, I'll make a try soon
But my goal is to stop to make BD25 because an optical disk is too much expensive versus a HDD :/

[foxyshadis]

Originally Posted by benwaggoner

Note you can make BD-25 compatible bitstreams WITH CRF. The -vbv-bufsize etcetera will still apply and keep things compliant.

For BD-25 and CRF 20, I'd recommend going down to a 25 Mbps peak and Level 4.0, which allows you to turn --slices 4 off. If you go down to a 15 Mbps peak, you can also use a 2 sec max GOP instead of 1 sec, and that might be just fine with CRF 20 and high-quality encoding settings.

I had no idea you could have a larger GOP depending on the bitrate. Thanks, that's incredibly handy to know! (Of course, the PS3 doesn't care anyway.)

[benwaggoner]

Originally Posted by foxyshadis

I had no idea you could have a larger GOP depending on the bitrate. Thanks, that's incredibly handy to know! (Of course, the PS3 doesn't care anyway.)

Yeah, it can be helpful when targeting lower average bitrates when you really weren't going to get peaks that high anyway.

Generally x264 does very nicely with 15 Mbps peaks for 1080p24 content.

[plonk420]

also, convert your lossless audio to 5.1 640kbps AC-3 (or, if you're okay with 448kbps, as previously mentioned)