Timeline editing

Some filters support a generic 'enable' option. For the filters supporting timeline editing, this option can be set to an expression which is evaluated before sending a frame to the filter. If the evaluation is non-zero, the filter will be enabled, otherwise the frame will be sent unchanged to the next filter in the filtergraph.

The expression accepts the following values:

't'

timestamp expressed in seconds, NAN if the input timestamp is unknown

'n'

sequential number of the input frame, starting from 0

'pos'

the position in the file of the input frame, NAN if unknown

'w'

'h'

width and height of the input frame if video

Additionally, these filters support an 'enable' command that can be used to re-define the expression.

Like any other filtering option, the 'enable' option follows the same rules.

For example, to enable a blur filter (smartblur) from 10 seconds to 3 minutes, and a curves filter starting at 3 seconds:

smartblur = enable='between(t,10,3*60)',
curves    = enable='gte(t,3)' : preset=cross_process

See ffmpeg -filters to view which filters have timeline support.