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Youtube recommend this encoding setting for videos. I'm is not an expert of encoding, I just use avidedmux to sync external audio with video, and compress the mix. There are a lot of options in "MPEG4 AVC" and I can't match it with the youtube's recommendations.

What options should I select in avidemux (for video and audio) to match youtube's recommendations?

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avidemux's dialog box for x264 settings is pretty bad. It's been years since x264 added presets from ultrafast to veryslow, but avidemux still makes you manually choose all the cpu-time vs. quality options. It doesn't even have a checkbox for more recent (but essential) options like mb-tree, or psycho-visual optimizations (AQ and psy-rd).

I honestly can't recommend avidemux (2.5.4 in Ubuntu 14.04) as a frontend for x264. It's pretty essential to have something with a slider for slow to fast presets. I made a test encode, and the important settings default to on, which is good.

It doesn't matter too much what you use for youtube, as long as you use enough bitrate for it to look good. (CRF 18 is usually visually transparent, you could go CRF 16 to be on the safe side.)

There aren't any settings that will make youtube use your encode untouched for even one of its standard resolutions, instead of doing a transcode. The encoding guidelines, are all stuff that's on by default in avidemux. Except the GOP of half the framerate, which makes no sense anyway, and is a horrible idea. They're going to xcode the whole video anyway, so using a 1/2 second GOP size is just going to hurt compression. Same for only 2 b frames. I'm sure their decoder can handle the max consecutive B frames h.264 allows. (which is probably 16, since that's what x264 allows.) x264's default setting of 3 b frames is apparently good. I think with that one, they're just making sure that mis-informed people don't disable b-frames and worsen the rate-distortion (quality vs. filesize) tradeoff of their encode.

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    Update: newer versions of avidemux seem to be much better, and does have x264 presets. And is all-around better at handling inputs in modern formats, too. – Peter Cordes Mar 21 '17 at 16:43

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