asetpts

Change the PTS (presentation timestamp) of the input frames.

setpts works on video frames, asetpts on audio frames.

This filter accepts the following options:

expr: The expression which is evaluated for each frame to construct its timestamp.
strip_fps (video only): Boolean option which determines if the original framerate metadata is unset. If set to true, be advised that a sane frame rate should be explicitly specified if output is sent to a constant frame rate muxer. Default is false.

The expression is evaluated through the eval API and can contain the following constants:

FRAME_RATE, FR: frame rate, only defined for constant frame-rate video
PTS: The presentation timestamp in input
N: The count of the input frame for video or the number of consumed samples, not including the current frame for audio, starting from 0.
NB_CONSUMED_SAMPLES: The number of consumed samples, not including the current frame (only audio)
NB_SAMPLES, S: The number of samples in the current frame (only audio)
SAMPLE_RATE, SR: The audio sample rate.
STARTPTS: The PTS of the first frame.
STARTT: the time in seconds of the first frame
INTERLACED: State whether the current frame is interlaced.
T: the time in seconds of the current frame
POS: original position in the file of the frame, or undefined if undefined for the current frame; deprecated, do not use
PREV_INPTS: The previous input PTS.
PREV_INT: previous input time in seconds
PREV_OUTPTS: The previous output PTS.
PREV_OUTT: previous output time in seconds
RTCTIME: The wallclock (RTC) time in microseconds. This is deprecated, use time(0) instead.
RTCSTART: The wallclock (RTC) time at the start of the movie in microseconds.
TB: The timebase of the input timestamps.
T_CHANGE: Time of the first frame after command was applied or time of the first frame if no commands.

Examples

Start counting PTS from zero
```
setpts=PTS-STARTPTS
```
Apply fast motion effect:
```
setpts=0.5*PTS
```
Apply slow motion effect:
```
setpts=2.0*PTS
```
Set fixed rate of 25 frames per second:
```
setpts=N/(25*TB)
```
Apply a random jitter effect of +/-100 TB units:
```
setpts=PTS+randomi(0, -100\,100)
```

Set fixed rate 25 fps with some jitter:

setpts='1/(25*TB) * (N + 0.05 * sin(N*2*PI/25))'

Apply an offset of 10 seconds to the input PTS:
```
setpts=PTS+10/TB
```
Generate timestamps from a "live source" and rebase onto the current timebase:
```
setpts='(RTCTIME - RTCSTART) / (TB * 1000000)'
```
Generate timestamps by counting samples:
```
asetpts=N/SR/TB
```