Fast 1st pass in x264

[thezanny]

Hello, I saw somewhere that when using the Fast 1st pass in x264, the encoding process is faster. I checked that and it's okay. Now, is there a quality loss? Is the quality loss visible ? Like, artifacts could be seen, or blurred pictures, something's like that?

PS : I'm using the x264 slower

[Atak_Snajpera]

no visible quality loss therefore developers decided to enable fast first pass by default.

[thezanny]

That's great. I only wanted to know that. So, I'll use Fast 1st pass.
Thank you atak

[jagabo]

If you use constant quality encoding (CRF mode in x264) there's no need for a first pass at all. With CRF encoding you specify the quality and the encoder uses whatever bitrate it necessary to deliver that quality. In 2-pass bitrate encoding you specify the bitrate and the encoder delivers whatever quality it can at that bitrate.

[fritzi93]

Yeah, I'm convinced one-pass CRF is the way to go if not encoding to put on optical media. Doing 2 pass to a target file size will yield wide variations in quality, because movies vary in length and compressibility. Animation like, for instance, WALL-E, will require much less space at a given CRF setting than an action movie.

BTW, faster presets using CRF will yield larger files with the same approximate quality than slower presets.

[thezanny]

But in CRF, I can't guess the output file. I did some 4GB video in CRF and the result came in as 8GB

[jagabo]

As we told you, when you use CRF mode you pick the quality, the codec picks the bitrate (and hence the file size). If you encoded that same file as 4GB it would end up with "half" the quality.

Bitrate based encoding is only useful when you need a file of a particular size. Ie, 4.3 GB to fit on a DVD, 716 MB to fit on a CD, etc.

[Hoser Rob]

There may be some quality loss with turbo 1st pass but nobody seems to complain too much.

You could try extracting a short snippet and encoding it both ways. See what you think. Quality is somewhat subjective. Not everyone agrees on what's good enough.

I use crf (constant quality in handbrake) too. Not because it's better than 2 pass ... none of the good docs like handbrake or avidemux claims that it is, though they do say it can be just as good.

Why I do use crf is that when I started learning how to use h.264 advanced settings 2 pass encoding was taking a ridiculous amount of time to encode. If you were to use all the h.264 tweaks you'd need one of those high performance cascaded pro machines, the sort you don't find in 'normal' computer stores.

So you can make an encode with crf much faster than 2 pass, without advanced settings, or crf with tweaked parameters and much better quality in the same time as 2 pass without.

However, some of my dvd rips are taking over 5 hours to encode in crf. That's really good quality, but just not doable for me in 2 pass.