I am having a problem with colour shifting as I transcode my XDCAM42250i sequence to an MP4...
I export from FCP using the 'Export to Quicktime Movie' setting, where the colours look more or less the same as in my canvas window on FCP. It is only once I convert it to an MP4 via Mpeg Streamclip, that the colours shift, making my clips look slightly pinkier. What's more annoying is that when I upload it to Youtube, the colours shift even more!
Every time you compress the video, you are messing with the color information. Smaller files mean less color data, so the colors won't look as good or vibrant as they did on your original, full quality source.
YouTube and Vimeo compress the footage YET AGAIN...even if you used one of their settings. Thus more information is tossed and it looks slightly worse.
This happens to us in TV all the time as well. We grade it according to our high end monitors, output to a high end tape or full res QT file. It's then compressed to a broadcast stream file that tosses out some color information. And then it is sent out over the airwaves or cable lines, further compressing it. And then it lands on a TV that might be calibrated, might not. So we have no control over how it looks once it leaves our hands. best we can do is make it look great before we export.
There are certain codecs that compress better. Which is why you hear about breakthroughs in compression. H.264 was a hit...and not H.265 is coming out with even better quality...less color loss and compression.