Bitrate, BPP or filesize: Capped?

[ocdboy777]

Is there some sort of Cap when it comes to Bitrate, BPP or filesize?

Source is The Dark Knight DVD ripped to HD.

Using generic.avi.xvid.audiocopy profile. 2 Pass Encoding. 720x304 Default Res.

Did some samples using the above settings and changed only "Fixed Bitrate" to 1500, 2000, and 2500. Even though the "Fixed File Size" box is grayed out, it changes to show the expected file size each time you change the "Fixed Bitrate".


1500 BR (.286 BPP) = File size box says 49MB (Actual size 49.4MB)

2000 BR (.381 BPP) = File Size box says 62MB (Actual size 52.7MB)

2500 BR (.476 BPP) = File Size box says 75MB (Actual size 52.7MB)

How is Fab creating a file with higher BPP and the file size stays the same?!

Out of curiosity, I did a test using a "Fixed File Size" of 53MB, since it seemed to be some sort of a capped limit.

The result was a Bitrate of 1629 (.310 BPP).

MediaInfo reports 2000, 2500 and 1629 Bitrate files at actual Bitrate of 1611Kbps.

This isn't making any sense to me? Does setting the Bitrate to higher than 1629 add any more quality? How could it if it doesn't add to the size of the file?

[signals]

Check the bits/pixel with MediaInfo, I think you will find it stays the same if you keep the framerate and output screen size the same. When the pixel buckets are full, they are full.

[ocdboy777]

Check the bits/pixel with MediaInfo, I think you will find it stays the same if you keep the framerate and output screen size the same. When the pixel buckets are full, they are full.

You are indeed correct. It seems that my samples maxed out at 1611kbps and .307 BPP. So, what lessons in encoding can I take away from this? This was just chapter 20 of The Dark Knight. Will encoding the entire movie at 1611 BR get the same result as encoding at 2000, 2500, etc...? Will this be true for any movie?

Am I right or wrong in thinking that the following is a good method:
1. Encode a couple chapters from source using 2500 RB.
2. Check mediainfo to find actual BR.
3. Encode entire movie using actual BR from sample as "Fixed Bitrate" setting.

Or am I trying to reinvent the wheel? Any suggestions on encoding methods would be helpful. Am I on the right track?

[ocdboy777]

Anyone care to chime in on this?

[ocdboy777]

I would edit my post, but the edit button seems to not be available. Anywho, nice to know that over 70 people have checked out the post, but only 1 person has offered any help so far. Thanks signals, hopefully you will log on again soon. heh

[signals]

The maximum usable bitrate is determined by the codec you are using and the Part or Level of the standard in use by the software, which determines the encoding matrix, bitrate, available resolution and other interrelated aspects (and can't be varied within DVDFab). You can read more about how this works here: http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC

You probably didn't get any other replies because your question wasn't really about a problem with DVDFab. I think there is no need to test encode to determine the actual bitrate; I generally just set it for a little over .3 b/p and run it that way with one-pass. Always looks good

[Ar-Pharazon]

I am having a strange issue with this kind of thing. Using 8.0.7.6 for ripping "pre-ripped" Despicable Me BD files (that's another issue, but I have a thread for that). And all other BD's I've used the same process with (so far) haven't had any output file issues.

When I move the slider up so the bitrate goes over 10,000 (from the "default" of 9575), I have been getting smaller output files (.avi) with lower quality.

I'm fiddling with this because this movie (so far the only one with trouble) has been getting a glitch during playback at the same time index after trying different quality levels during ripping.

I've tried 1-pass & 2-pass encoding and changing the bitrate and therefore bits/pixel level.

Going with 1920x1040 with the default level, I get a 4.9GB output file which looks & sounds amazing, but always has the glitch (errors out). The attempts at going over 10,000kbps gave me a 1.3GB file.

Once I tried doing it as an .mp4, but DVDFab only considers .mp4 for iphone & ipad, so the quality wasn't good, but there wasn't the glitch.

I just finished a go with it at 8611 kbps, still good quality (4.8GB) but same glitch.

Why is it giving me a lower output filesize with higher quality settings?

[Ar-Pharazon]

Just for kicks, I ran the slider to the top, 50,000kbps.

Output file: 1.2GB, looks like crap but no glitch.

[signals]

You may be exceeding what the codec can do with the way it is set up to accomodate that profile. Try the iPhone 4 profile that does 1080, I have had good luck with that. Others have also reported problems with two-pass, but I almost never use it so I can't add much there. I have the Despicable Me BD here and as time permits will see if I can induce the problem you are seeing.

[Ar-Pharazon]

If your DVDFab opens the BD on it's own, you're ahead of me already

I've heard the terms "seamless branching" & "file change" related to the Despicable Me BD, indicating the glitch might occur at the point it changes from one .m2ts file to another.


Edit: OK, the glitchy time index occurs within an .m2ts file, so it's not a point between files.

[Ar-Pharazon]

DVDFab did finally open the BD itself. Took around 5 minutes.

Ripped to the same default settings, same result, glitch at 1:25:07.

So, [other software] is ruled out as far as that goes.