What's the difference between 2nd pass and two pass in h.264 encoders?

[Stears555]

Hello guys!

What's the difference between 2nd pass and two pass in h.264 encoders? Which one is the better? There are (at least) three main encoding options in many h.264 encoders: 1st pass 2nd pass and two pass. I know that 2nd pass and two pass are not the same.

Thank you for your reply!

[Selur]

I'm surprised you weren't able to answer this by doing some simple search,...


encoders normally have:1. one pass encoding methods (average bitrate, constant quantizer, constant rate factor and similar)
2. n-pass encoding methods, which consist of two passes, a first pass which is normally done to collect a bunch of statistical data (possible, key frame positioning, some complexity measurement etc.) and following passes which use the data from the previous pass to archive a better rate control. If the used encoding method supports more than two passes, all passes will update the statistical data file. (for most encoders more than two passes are a waist of time)


Note that due to the nature of rate control only with n-pass encoding it is possible to in example archive a specific file size and at the same time try to optimize the quality.


so:
1st pass = the first pass of a n-pass encoding scheme
2nd pass = 2nd pass of a n-pass encoding scheme (requires that a first pass was run before, so that a statistical data file is present)
two pass = a special mode offered by most guis which will run the 1st and 2nd pass automatically one after another, so that the user does not have to start them manually.