Tumblr video pixelated? Upload 720p H.264 MP4, not a 360p source

Tumblr transcodes and re-compresses every uploaded video, so some light pixelation can appear. Its advice is to export as close to its transcoder's goal as you can: a 720p H.264 MP4. If the source is smaller than 720p, the page says nothing can really improve it without upscaling software, which might add artifacts.

What does Tumblr's page actually say?

What resolution should I generate?

Generate at 720p. Sume Auto create controls default to 720p and 8 seconds, with 3 to 10 second clips at 16:9 or 9:16, so the default already matches Tumblr's target. Avoid the 360p tier on Gemini Omni Flash 1.1: a 360p source is below the target, and Tumblr's page says a smaller source will not be improved. See Video Router.

Does trimming add another pass?

Trim's default exact precision is a frame-accurate re-encode with libx264 and yuv420p, so the output is H.264. The optional output conform takes width and height from 256 to 2160, in exact mode only; omit it to inherit the source size. If you do not need a cut, skip the trim, since every re-encode is one more lossy step before Tumblr applies its own. Related: what exact mode re-encodes.

Will 720p remove all artifacts?

No. Tumblr says some light pixelation can still occur after its transcode. Matching its target reduces the gap; it does not remove the re-compression.