Difference between export VBR 1 pass and VBR 2 pass

[Cinema Físico]

 Hello what is the difference between export VBR 1 pass and VBR 2 pass? In which ocassion should I use VBR 1 pass and VBR 2 pass. 

Thank a lot

[Steve Griffiths · Accepted solution]

The first pass in a Variable Bitrate 2 pass encode is an analysis pass which looks at the video content of the program and looks for high motion, low motion and complexity. It then uses this analysis data on the second pass when actually encoding to assign more 'bits' to the scenes that have (say) high complexity motion and less 'bits' to (say) static scenes with no or little motion.

1 pass VBR just encodes 'on the fly' and can't encode frames 'knowing' what's further long in the program.

Effectively 2 pass VBR will give you better encodes at a slightly lower datarate than 1 pass VBR. Both usually provide better (or as good) encodes at significantly lower oevral file sizes than CBR (Constant Bitrate).

My advice. As long your encodes are set to reasonable datarates and you don't specifically need the absolute smallest possible encodes (file size) ... 2 pass VBR is generally not worth the extra time it takes*.

Hope this helps.

* I have one client that needs most encoded programs to be lower than 50MB in size. To hit this target we use 1280x720 instead of HD, VBR 2 pass, 1.4MBit average data rate and audio encoded mono at 96k ... but this is an outlier requirement and often they still look like crap but 2 pass makes them slightly better 🙂

[Steve Griffiths]

To clarify:

2 pass VBR can give you the same quality as 1 pass VBR but at a lower datarate.

OR better quality than 1 pass VBR at the same datarate.

[Ann Bens]

Filesize = bitrate x duration.

Framesize is irrelevant.

[Steve Griffiths]

True, but a smaller frame size i.e. 1280x720 instead of 1920x1080 - at the same bitrate - can provide an 'apparent' improvement in visual quality when working with lower bitrates.

[chrisw44157881]

same with reduced framerate and more delta frames. pure bitrate is kind of a mis-normer. they've been making pixel/bit calculators for a long time that figures all this stuff out.

[Mariana22794724tke0]

Hello, quick question, what do you mean by reasonable datarates?

[R Neil Haugen]

"Reasonable" depends on several variables, like

• framerate of the sequence, as more frames per second requires higher data;
• framesize of sequence, as larger image size means more pixels needed per image to get same visual resoloution;
• amount of motion per frame within the image;
• amount of fine detail in-focus ... especially if that is moving and ...
• what you see visually as "usable".

So to answer, you'd get more a a chart with a number of if-this/then-try-that settings.

I've seen several posts on blogs and YouTubes on data rates for different things. It's about as deep a rabbit hole as color can be ...

Neil

[Richard M Knight]

Also, I think you'll find, there is no option for 2 pass encoding if the export is using Hardware acceleration.

[Vladimir5C3C]

I'm using Hardware acceleration and I have VBR 2 pass encoding option.

[chrisw44157881]

it may not be greyed out, but it won't be accelerated by the gpu.

[Prajjwal5E15]

i want to ask that how musch difference does it make if your bits are set at 25 mb (max at50 at VBR 2 pass) to 20mb(max 40 VBR 2 PASS)

does the video quality gets effected?

[Richard van den Boogaard]

This depends on the resolution of your sequence. If you're encoding a 1080p file, anything above 20 Mbit/s will be off high quality. For a 4K file, it's on the lower end of the spectrum.

Just look at the settings for the preset "High quality 1080p HD": it's pre-defined at 20 Mbit/s.

On another note, I would advise against the use of VBR 2 Pass encoding if your exports are being used on social media. Due to the sheer volume of content the encoders of YouTube, Facebook and the like get to process, they simply ignore highly efficiently encoded (2 Pass!) content. 2 Pass means that all available - prior - bit reservoirs inside the file get filled to the brim, to accomodate for high motion frames versus low motion frames. If you're going out to these social media, go for a higher bitrate in CBR 1 Pass mode.

Hope this helps.

[Craig16E5]

Is there any way to get gpu acceleration when using VBR 2-pass? Quality is more important to me than filesize, but it's obscenely longer to render 2-pass due to the lack of gpu support. 

[Pera M.]

To my knowledge, that's not possible. Can you really see the difference between VBR 1 pass and VBR 2 pass?

[RjL190365 · Accepted solution]

As I stated in several other threads, nobody (hardware-wise) currently supports hardware acceleration for 2-pass VBR. Adobe has absolutely no control over this fact.