RCModelReviews wrote:I did some tests a while back and the bitrate for 1080p from YouTube was the same whether you uploaded in 1080p or 4K. If you want reasonable upload times then a high-quality H265 file at 1080p is going to give better results than an upscaled 4K file of the same size (at an obviously lower quality).
I don't find that to be the case with x264 at least, based on quality metrics.
Here I took a 2160/50p Cineform (Filmscan 2) transcode of the CrowdRun sequence used in the test series I referred to above:
https://forum.blackmagicdesign.com/viewtopic.php?f=21&t=83493&p=464648#p464456 I down-scaled/transcoded the Cineform file to 1080/50p x264 at CRF=14. The bitrate of the resulting encode was 90Mbps. So I transcoded the file to x264 again as 2-pass encode with a target bitrate of 90Mbps at both 1080/50p and the original 2160/50p resolution. The resulting bitrates were confirmed to be 90Mbps.
I then uploaded both (2-pass) encodes to YouTube and downloaded the YT 'converted' 1080/50p files revealed by 'YouTube Info'.
https://www.h3xed.com/blogmedia/youtube-info.php In fact, with 4K uploads, YouTube encodes both vp9 (webm) and AVC (mp4) files at 1080p, but with 1080p uploads it only encodes AVC mp4.
I then ran SSIM quality metrics on the downloaded 1080/50p files (using the 90Mbps 1080/50p x264 upload file as reference).
With the 1080/50p x264 (90Mbps) upload the SSIM score of the 1080/50p AVC (mp4) YT download was 84.197. The file bitrate was 5899 Kbps.
With the 2160/50p upload, the results were:
1080/50p AVC (mp4) download, SSIM: 84.194, Bitrate: 5895 Kbps
1080/50p vp9 (webm) download, SSIM: 86.874, Bitrate: 6427 Kbps.
So there was no difference in the metric quality (and bitrates) of the YT converted 1080/50p AVC mp4 files, but the 1080/50p vp9 (webm) encode from the 2160/50p upload was measurably higher quality and a slightly higher bitrate.
Here are the respective YouTube videos:
Incidentally, the uploaded 1080/50p x264 CRF=14 transcode (90Mbps) produced similar results to the 90Mbps 2-pass x264 uploads:
1080/50p AVC (mp4) YT download, SSIM: 84.531, Bitrate: 5926 Kbps
Edit: I also uploaded a 2160/50p x264 CRF=14 transcode of the original Cineform source. Obviously the encode bitrate was much higher - 509 Mbps. The downloaded YT 1080/50p files gave the following results:
1080/50p AVC (mp4) download, SSIM: 84.635, Bitrate: 5955 Mbps.
1080/50p vp9 (webm) download, SSIM: 87.351, Bitrate: 6546 Mbps.
So uploading at the higher (5.7 fold) bitrate did bring about a small improvement in the (metric) quality of the YT 1080/50p encodes, the vp9 file more so than the mp4 file.
Again, here are the respective YouTube videos: