Editing Pro Tools (section)

=== Timeline ===
The timeline provides a graphical representation of all types of tracks: the audio [[Envelope (waves)|envelope]] or [[waveform]] (when zoomed in) for audio tracks, a [[Piano roll#In digital audio workstations|piano roll]] showing MIDI notes and controller values for MIDI and Instrument tracks, a sequence of frame thumbnails for video tracks, audio levels for auxiliary, master and [[Variable-gain amplifier#Digital variable-gain amplifier|VCA]] master tracks.{{Sfn|Avid|2019|p=190|loc=12. Pro Tools Main Windows}} Alternate audio and MIDI content can be recorded, shown, and edited in multiple layers for each track (called playlists), which can be used for track compositing.{{Sfn|Avid|2019|p=691|loc=32. Playlists}} All the mixer parameters (such as track and sends volume, pan, and mute status) and plug-in parameters can be changed over time through [[Track automation|automation]].{{Sfn|Avid|2019|p=1125–1126|loc=50. Automation}} Any automation type can be shown and edited in multiple lanes for each track.{{Sfn|Avid|2019|p=1135–1138|loc=50. Automation}} Track-based volume automation can be converted to clip-based automation and vice versa;{{Sfn|Avid|2019|p=947|loc=43. Clip Gain and Clip Effects}} automation of any type can also be copied and pasted to any other automation type.{{Sfn|Avid|2019|p=1160|loc=50. Automation}}

Time can be measured and displayed on the timeline in different scales: bars and beats, time or SMPTE timecode (with selectable frame rates), audio samples, or film stock feet for audio-for-film referencing (based on the 35&nbsp;mm film format).{{Sfn|Avid|2019|p=837–840|loc=38. Time, Tempo, Meter, Key, and Chords}} Tempo and meter changes can also be programmed; both MIDI and audio clips can move or time-stretch to follow tempo changes ("tick-based" tracks) or maintain their absolute position ("sample-based" tracks). Elastic Audio must be enabled to allow time stretching of audio clips.{{Sfn|Avid|2019|p=16|loc=2. Pro Tools Concepts}}