As I said, that’s what I’m going to do for the next projects. But for the final file (no more processing is done on it), I mean the file that I spread among customers who may watch the file on a laptop or mobile phone without headphones, I prefer to give them the maximum volume.
By the way, I figured out the problem: it was a mono/stereo-mismatch. I had a QT Animation file with 2 channels, and when rendering out a mono .mp4 file, QuickTime somehow messed up the overall volume. The final file was playing fine in QuickTime as well as Windows Media Player, but the same file clipped in VLC and on YouTube after uploading.