A video frequently looks worse immediately after publishing than it does the next day. The picture has not changed; the available versions have.
Processing happens in stages
An upload is not encoded once. The platform produces a set of renditions at different resolutions and, increasingly, in more than one codec.
Lower resolutions encode quickly and are published first, so the video becomes watchable within minutes rather than after the full set is complete.
Higher resolutions take considerably longer, and the most efficient codecs longer still, which is why the top quality option appears late.
Encoding is a queued, shared resource
Platforms process an enormous volume of uploads with finite capacity, so every upload waits in a queue alongside everyone else's.
Queue position depends on load, and the same file uploaded at different times can finish processing at very different speeds.
Videos expected to attract large audiences are often prioritized, since the cost of a poor first-hour experience is proportional to how many people have it.
Not every video gets every codec
The most efficient codecs cost far more to encode, so platforms apply them selectively rather than universally.
A common approach is to encode everything with a widely supported codec and add a more efficient version once a video accumulates enough views to justify it.
This is why an older video with a substantial audience can offer a smoother high-resolution experience than a new upload of identical source quality.
What the source file controls
Everything downstream derives from the upload, so its quality sets a ceiling that no processing improves.
Uploading at a higher resolution than the intended viewing resolution generally helps, because the platform allocates more bitrate to larger renditions.
An export with insufficient bitrate arrives already carrying artifacts, and the platform's encoder faithfully preserves them into every rendition it produces.
Frame rate is worth matching to the source as well, since converting between rates during export introduces motion irregularities that survive every stage afterwards.
Publishing timing follows from this
The practical consequence is that a video should finish processing before it is promoted, not while the audience is arriving.
Uploading well ahead and scheduling publication achieves that, and it costs nothing beyond planning the upload as a separate step from the release.
Creators who upload and immediately share a link are showing their most engaged viewers the lowest-quality renditions the platform will ever serve.
Most platforms indicate processing state somewhere in their upload tools, and waiting for the highest resolution to appear before promoting a video costs nothing but patience.