I know I started a similar thread not too long ago, and I also know that the current branch focuses on newer codecs like x264 and x265, but I've been playing around with both Avidemux 2.5.6 and 2.6.8 and I've seen that, at least for Standard Resolution encodes, Xvid with the 'KVCD Notch' quantization matrix at relatively high bitrates (1900-2300 kbps) gives me a better picture quality than x264. And with "better" I mean "sharper". And the backgrounds keep surprisingly 'quiet' and 'noise-less'. It simply looks awesome. It might have something to do with H264's wonderful in-loop deblocking filter, which smoothes everything a bit. This is usually unnoticeable in HD, preserving film grain and detail, but gets pretty obvious at lower resolutions, even if one increases the bit rate. My brother had a really frustrating experience a few years ago backing up his South Park DVD collection using x264 for video through Mencoder and the only way he could get a sharp picture was through sharpening filters like MSharpen, which slows the encoding process significantly. I can understand that.
Is there a possibility to re-add custom quantization matrices in the near future? Not only for Xvid, but also for MPEG-2 and libavcodec MPEG-4...
Truth is, I like the 2.5.x branch, but I like the current branch even more. I just miss the possibility to use custom matrices. Avidemux is my favorite piece of software for video encoding, and I'd really like those options to be added back.
Cheers!