Inside the project everything stays synchronized, yet the exported H.264 MP4 gradually loses sync. The output is 4K and fairly high bitrate. What is the fastest way to tell whether the render is genuinely wrong or my computer simply cannot play the final file smoothly?
Play the export in at least two independent decoders, preferably on another device too. If every decoder shows the same timing error, suspect the export. If only one machine struggles, playback performance can imitate sync problems.
Render the same 60-second problem section once with hardware encoding and once with software encoding, keeping frame rate and audio settings the same. That isolates the encoder path quickly.
Editing workflows
Inspect phone/OBS/screen-recorded sources for VFR. A timeline can look acceptable during normal preview and still reveal timestamp problems during a deterministic export.
Codecs & export