Quote:
Originally Posted by kurkosdr
Looks like youtube beat us: I found this and it's quite useful (just set the bitrate to 4000) |
I can't speak for every XviD build but the version which comes with AutoGK automatically provides the appropriate VBV values according to the profile you select and doesn't seem to let you change them anyway.
The main difference I can see between following the video's instructions and encoding with AutoGK is you're selecting the target bitrate rather than the target file size, but it's still 2 pass encoding only you're guessing as to what the quality will be.
The video suggests using Average Bitrate 2 Pass encoding while setting the bitrate to 1500 or 2000. Is that really any different to 2 pass encoding while selecting the file size except you're selecting it in a different way? Seems to me like it's a method which also predetermines the quality, while potentially wasting a lot of bits or reducing the quality through restricting it too much.
I've got a bunch of AVIs on my hard drive waiting to be burned. The largest has a bitrate of around 1800 while the smallest has a bitrate of 730, yet they were both encoded to the same quality setting (AutoGK's 75%).
One thing I've never understood is how AutoGK determines the quality after running a compression test or after it's run the first pass. I gather 75% = Q2.7 but I don't know how the quality is determined. I assume the info is obtained from XviD's first pass log, I just don't know how.
Likewise I've never understood why AutoGK is the only GUI I've ever come across which supplies that info. Why is it not standard for a GUI to run a first pass according to your settings then tell you what the quality will be? I guess the same question would apply to x264 encoding as well.
Thinking about it a bit more (and sorry for wandering off topic a bit) why is it not possible to run a 2 pass encode at a selected quality rather than file size or bitrate?
It's my understanding XviD runs it's first pass using Q2 and then adjusts the bitrate etc for the second pass according to the selected file size. If that's correct, why can't it also make adjustments to achieve a selected quality?
I understand as a general rule it'd probably be pointless (might as well just run a single pass encode at a selected quality) but when it comes to VBV control you're forced to run 2 passes, so being able to do so while simply selecting the final quality rather than guessing at a file size would be nice.
Or even the ability to manually calculate the desired quality/file size based on the stats from the first pass, then use the calculated file size for the second pass to achieve the desired quality. Is that possible?