Multipass Encoding

[lcphr3ak]

Hi,
This is rather just a question to understand how it works. I think I understand how 2-pass encoding works, where the encoding software analyzes the movie through the first pass, writing down the data to a log file; then utilizing the logged data to compress the video through the second pass. My question is, how does a single pass work? As simple as it sounds, I can't seem to find the answer . It's probably stupid to ask this, but I just am not 100% sure what makes the difference, as in why that logged data isn't analyzed and used the first time around, instead of making it a two step process. I'm sure finding out how a single pass works will give me an understanding.

Thanks in advance!

[guns1inger]

The second pass lets the encoder refine the first pass with the benefit of hindsight. A single pass VBR encode always runs the risk of allocating too little data early on, and having surplus at the end of the encode, or too much at the start, and having to starve the clip in the latter stages if it is to meet a file size (or true average bitrate). The second (and in the case of CCE, subsequent) pass(es) allows for corrections to be made and a better allocation of data to be applied across the entire clip.

[lcphr3ak]

The second pass lets the encoder refine the first pass with the benefit of hindsight. A single pass VBR encode always runs the risk of allocating too little data early on, and having surplus at the end of the encode, or too much at the start, and having to starve the clip in the latter stages if it is to meet a file size (or true average bitrate). The second (and in the case of CCE, subsequent) pass(es) allows for corrections to be made and a better allocation of data to be applied across the entire clip.

Ah, alright, I get it now. It's like double-checking/optimizing its work.

Thanks!

[redwudz]

Just to add, a single VBR encode pass won't let you set a filesize, if that's important to you. A two pass VBR encode will. If filesize isn't important, use a single pass VBR or use a quality based single pass encode instead.

The quality encode would be my choice over a single pass VBR encode most times. Again, if you are not concerned with filesize.