A score and a recording of it go in. A video comes out with every note in time, including the places the player slowed down. No tapping, no page marks, no timeline.
Your files never leave your computer. The video is made here, in this tab.
To sync sheet music to audio, drop a score (PDF, MusicXML, MIDI or Guitar Pro) and a recording (MP3, WAV, M4A, MP4 or MOV) on this page. The notes line up by themselves, rubato included. Pick a look and export an MP4. The first minute is free with a small mark.
The real performance, with the score following it.
A phone video and the file you played from.
They see the bar you are on as they listen.
Bring the score the player actually played from. If the take repeats a section the file does not, or skips one, that is handled, and it says so.
A clear recording of a solo instrument is the easiest case, and a band or a noisy room works too. Choosing the part you can hear best helps.
Check the result in the player here. If a bar needs a nudge, the studio lists anything worth a second look and lets you move it by hand.