Why is size so tough to predict now?

[abbadon]

I'm guessing this is a rebuilder question, though it may be an x264 question (please move if so). It seems it is quite hard to predict the final size of an encode compared to former times, i.e. xvid on cd, dvd9-dvd5, even rebuilding to BD5 or BD9, where the output will be within 1% of 1% of setting. Even with ABR or CBR or two pass there can be up to a GB off in a BD25. Is this just the beta state of things, to be fine tuned as time goes on, or there some fundamental reason sizes are harder to hit?

Now that I'm doing more BD50 -> BD25 I find myself doing two encodes for each, changing the custom size, to get within at least 1%.

Maybe I'm a bit picky, or maybe I'm doing something wrong (all defaults, full minus foreign language, custom size). This has just been eating away at me ...

[jdobbs]

It's not really an X264 issue. It's muxing to M2TS. M2TS has more overhead than other formats like MKV -- and there isn't much consistency. The overhead also changes between the video formats (VC-1, MPEG-2, and AVC) -- and even more so for the different audio formats (LPCM, DTS, DTS-HD, AC3, True-HD, etc.) with even more inconsistencies depending upon sample rates and bitrates. The same holds true for subtitles (PGS streams)

For example... did you know that sometimes muxing a 192Kbs AC3 stream into an M2TS can result in a file that is the same size (or possibly larger) than the exact same stream at 224Kbs? The source files may differ by 16%, but not the output. Odd but true.

So the bottom line is that you are doing a lot of "educated guessing". I did a boatload of testing in which I muxed variants of all the different components way back when I first started BD-RB. In the end I created a table of adjustment values depending on several factors of all the acceptable formats. I then left enough space to cover possible inaccuracies. So essentially when you use custom sizes, you're throwing away all the work that went into that... The price you pay is having to occasionally start over.

[abbadon]

ok, makes perfect sense

when you use custom sizes, you're throwing away all the work that went into that...

sorry

[jdobbs]

ok, makes perfect sense



sorry You don't have to be sorry... I didn't mean it as a criticism...

[Todd Sauve]

As long as the program compresses the file to a size that will still fit on the desired disc, i.e., DVD9 or DVD5, I am a happy camper! And BD Rebuilder seems to do it every time I use it, so kudos to jdobbs for a truly great program! :)

Now if it could only cut the coding time in half ... just kidding!

By the way, does running the program on Win 7 64 bit speed up the coding process at all?