AVIDemux 1-pass vs. 2-pass Configuration Question

[robindean]

Hello again everyone.

With the help of people on these forums, I've successfully managed to get AVIDemux to work with AVISynth and am happy to say that my video effort is coming along smoothly.

I spent the better half of yesterday reading about all of the different AVIDemux settings on wikipedia.

Because I have all the time in the world to encode (I've been leaving it running over night), I've selected each of the most CPU intensive settings. I decided to do this in hopes of getting the best possible output within the boundaries of my intended use.

My intended use: .mp4, 640 kbps, CBR, Loaded into flash as a background video.

MY QUESTION:

Using the Constant Bitrate option within the .mp4 configuration plainly states that it is a 1-pass setting. The "Average Bit Rate" setting, on the other hand, is 2-pass.

If I use the ABR setting and set the bit-rate variance threshold to 0 (making it CBR) am I going to get better quality due to it being 2-pass?

I feel this question is program dependent and, being new to AVIDemux, figured it might be good to ask those who know better than I.

[redwudz]

If you made it CBR, then then you would defeat the purpose of making two passes. The idea with a two pass encode is that the first pass checks the file and determines what bitrate you need for the various scenes, then the second pass applies that information. This gives you control over the filesize. The quality there is set by the average, low and high bitrate settings. Setting higher thresholds with VBR will give you better quality, but larger filesizes.

A single pass gives you control over the quality, but not the filesize. Depending on the bitrates used, two pass or constant quality can give you the same quality, but with different end filesizes.

But someone else here may be able to give a better answer.

[robindean]

I think you covered it.

One reason I asked was because with programs such as VisualHub (now open source), 2-pass encoding operated in a completely different manor. That particular program would perform a "starter run" encoding process which produced output to a hidden directory. Then, it would investigate the end result and see if it could modify the procedure in any beneficial way before encoding the final output.

Your response suggests to me that AVIDemux performs, even in it's first run, extremely specific data analysis based on the user configuration.

Pretty cool.