The result may not look the best when compared to the source when played on the computer, but on YouTube it can look significantly better compared to YouTube's reencode of the unfiltered version.Removes black bars on ultrawide videos and offers advanced options to fix aspect ratio. I still have no idea what you're using for this, but AviSynth and the x264 encoder (with a GUI, if you like) can do that easily.

I'd filter it properly myself before ever uploading it, and then upload just the 720p version. I wouldn't submit an upscaled and detailed 1080p version and then play the 720p version of it expecting to get the better smooth quality. Since you prefer the softer versions of your uploads, I don't think it necessary to jump through hoops to get them. Although it's usually said the better quality (=higher bitrate) the upload, the better quality the YouTube version, the difference will be minimal at best. Here's the 720p source encoded at 300000 kbps / 384kbps aac which didn't make a visible difference in terms of quality or recompression when encoded by Youtube. The best I managed to recover is a session from a month back.

Upon reboot, the 50+ Firefox tabs I'd hoarded over the past months were gone: no crash session restore page, just my browser homepage. My graphics driver inexplicably BSOD'd when Flash started playing back the native 720p YouTube page the second time. But even if your video has those tiny details, it's worth losing them for the sake of the rest of picture. Certain very fine details are better reproduced in the 720p version than either of the upscale-compress-downscale versions, for example the microphone in the second image row and the bass guitar strings in the bottom row. I think the benefits of upscaling to 1080p are questionable, but for 1440p it's obvious. For 720p, there are two streams so I grabbed the one with the slightly higher video bitrate. MP4s were saved using Complete YouTube Saver. So I went with Spline36Resize for upscale & downscale.

Initially I used nnedi3_rpow2 to upscale, but then I noticed that confounds the results for a source like this: it straightens lines that are aliased in the original, making the downscale too smooth. Captured as Ut Video, but for upload to YouTube I removed every other frame and recompressed with ffdshow's Huffyuv since I know it can process that. You could prepare short 10-15 second samples without much time and effort.

Fake 4k videos on youtube