[x264]How to get the exact or needed file size using crf?

[mars0001]

I usually encodes dv captures with x264 using 1pass with crf option. In this case the final file size is not my concern.

But when I want to encode ripped vobs using 1pass with crf option, I don't know how to reach the needed final file size (actually 700mb).

Is it possible to get a 1cd of x264-encoded mp4 file using crf option?

Anyway the reason I insist using crf [CQ-ASP_Q2_eq(crf) in MeGUI] is that I think it can produce better quality than ABR[1P-goodquality in MeGUI] does. Is it correct?

Thanks in advance.

[Sharktooth]

How to get the exact filesize using xvid quant 2?
Not possible... and the same thing is valid for x264.
multi pass encoding was made to hit an exact filesize...

[Audionut]

Anyway the reason I insist using crf [CQ-ASP_Q2_eq(crf) in MeGUI] is that I think it can produce better quality than ABR[1P-goodquality in MeGUI] does. Is it correct?

Yes. Mostly.

But as Sharktooth said, it's impossible to get an exact size using --crf.

If you must hit a desired file size, use 2 pass.

Else, encode say 10% of the video at --crf whatever. If the resulting bitrate of that encode is less than the target you are after, and the quality of that encode is good enough for you, then your set. But that would be a fair amount of trial and error.

[bond]

the point of crf is to get constant quality without caring about the filesize

if you want to get a constant quality while caring about the filesize use the bitrate related options (1 or 2pass)

[jumbo]

by the way, can I analyze 1st pass using crf then doing 2st pass?

[foxyshadis]

Yes, add --pass 1 to the command line.

[BlackSharkfr]

this may be a noob question, i've never really used the quality based modes but ... what is the difference between crf and qp modes ?

[Audionut]

"qp" will encode all frames at the specified quantinizers.

"crf" will vary the quantinizer slightly, to give more bitrate to scenes that need it, and less bitrate to scenes that don't, while still mainting the average quantinizer that you set.

edit: If you don't need to hit a desired file size, "crf" is an excellent way of encoding at a constant quality. Where as "qp" will blindy encode all frames at the same quantinizer.

[akupenguin]

quantinizerquantizer

[mars0001]

Thank you for all the answers.
Now I understand the difference between qp and crf.
So when I want to make a backup CD of 700mb I'll use 2pass but if I just want to make a backup file of DV capture where the exact file size is not a concern I'll encode it with 1pass crf.

Many thanks again.