FPS Filters

A set of functions to change the frame rate of a clip:

  • AssumeFPS changes the frame rate without changing the frame count.

  • AssumeScaledFPS is similar to AssumeFPS, but works by directly scaling the frame rate numerator and denominator.

  • ChangeFPS changes the frame rate by deleting or duplicating frames.

  • ConvertFPS attempts to convert the frame rate without dropping or inserting frames.

AssumeFPS

Changes the frame rate without changing the frame count, causing the video to play faster or slower. AssumeFPS can be called 4 different ways, as documented below.

Syntax and Parameters

AssumeFPS (clip1, clip2, bool "sync_audio")
AssumeFPS (clip, float fps, bool "sync_audio")
AssumeFPS (clip, int numerator, int denominator, bool "sync_audio")
AssumeFPS (clip, string preset, bool "sync_audio")
clip, clip1

Source clip; all color formats supported.

clip2

If supplied, the new framerate is taken from this clip.

fps
If supplied, the new framerate is set to fps.
Due to the way frame rates are stored, fps must be converted to the closest ratio of 32-bit signed integers, eg, 33.3333 → 329833/9895 (33.3332996)
numerator, denominator

If supplied, the new framerate is set to numerator divided by denominator. If only the numerator is given, denominator defaults to 1.

preset

If supplied, the new framerate is taken from a set of standard rates, as shown below:

preset

numerator

denominator

approximate FPS

"ntsc_film"

24000

1001

23.976

"ntsc_video"

30000

1001

29.970

"ntsc_double"

60000

1001

59.940

"ntsc_quad"

120000

1001

119.880

"ntsc_round_film"

2997

125

23.976

"ntsc_round_video"

2997

100

29.97

"ntsc_round_double"

2997

50

59.94

"ntsc_round_quad"

2997

25

119.88

"film"

24

1

24.0

"pal_film"

25

1

25.0

"pal_video"

25

1

25.0

"pal_double"

50

1

50.0

"pal_quad"

100

1

100.0
sync_audio
If true, the audio sample rate is changed by the same amount; the pitch of the resulting audio is shifted.
If false, the audio is unchanged; this means the audio will lose synchronization over time.

Default: false

Examples

PAL +4% conversion:

AVISource("FILM_clip.avi") # Get 24fps clip
LanczosResize(768, 576)    # Resize to PAL square-pixel frame size.
AssumeFPS(25, 1, true)     # Convert frame rate to PAL, also adjust audio.
SSRC(44100)                # Restore audio sample rate to a standard rate.

  • The +4% speed up is conventionally used for displaying 24fps film on PAL television. The slight increase in pitch and tempo is readily accepted by viewers of PAL material.

Slowing down of video (framerate of original video is 30 frames a second):

AviSource("video.avi")
AssumeFPS(10, true) # Slows the video down to a third of its speed

Speeding up of video (framerate of original video is 30 frames a second):

AviSource("video.avi")
AssumeFPS(60, true) # Double speed

sync_audio experiments:

ColorBars() ## 29.97 fps
Trim(0, 299) ## vdur (video duration) = 10.01 sec
A = Tone().AudioTrim(0, -9.0) ## adur (audio duration) = 9.00 sec, sample rate=48000
AudioDub(A) ## vdur=10.01, adur=9.00
#return AssumeFPS(24, sync_audio=false) ## vdur=12.50, adur=9.00 (audio unchanged)
#return AssumeFPS(24, sync_audio=true)  ## vdur=12.50, adur=11.238, sample rate=38438
## (audio sample rate is changed by the same amount - in this case, by 24.00/29.97)

AssumeScaledFPS

Scales the frame rate without changing the frame count, causing the video to play faster or slower.

It is similar to AssumeFPS, but works by directly scaling FrameRateNumerator and/or FrameRateDenominator.

The AssumeScaledFPS filter scales the frame rate without changing the frame count. The numerator is multiplied by the multiplier, the denominator is multiplied by the divisor, the resulting rational FPS fraction is normalized, if either the resulting numerator or denominator exceed 31 bits the result is rounded and scaled. This allows exact rational scaling to be applied to the FPS property of a clip.

Syntax and Parameters

AssumeScaledFPS (clip, int "multiplier", int "divisor", bool "sync_audio")
clip

Source clip; all color formats supported.

multiplier

clip.FrameRateNumerator is multiplied by multiplier.

divisor

clip.FrameRateDenominator is multiplied by divisor.

sync_audio
If true, the audio sample rate is changed by the same amount; the pitch of the resulting audio is shifted.
If false, the audio is unchanged; this means the audio will lose synchronization over time.

Default: false

ChangeFPS

Changes the frame rate by deleting or duplicating frames.

The audio data are not touched by this filter. Audio will remain synchronized, although the length of the audio data may slightly differ from that of the video data after the conversion. This is because the output can only contain an integer number of frames. This effect will be more pronounced for shorter clips. The difference in length can be ignored. ChangeFPS can be called 4 different ways, as documented below.

Syntax and Parameters

ChangeFPS (clip1, clip2, bool "linear")
ChangeFPS (clip, float fps, bool "linear")
ChangeFPS (clip, int numerator, int denominator, bool "linear")
ChangeFPS (clip, string preset, bool "linear")
clip, clip1

Source clip; all color formats supported.

clip2

If supplied, the new framerate is taken from this clip.

fps
If supplied, the new framerate is set to fps.
Due to the way frame rates are stored, fps must be converted to the closest ratio of 32-bit signed integers, eg, 33.3333 → 329833/9895 (33.3332996)
numerator, denominator

If supplied, the new framerate is set to numerator divided by denominator. If only the numerator is given, denominator defaults to 1.

preset

If supplied, the new framerate is taken from a set of standard rates, as listed under AssumeFPS.

linear

If true (the default), this will make AviSynth request frames in a linear fashion when skipping frames.

Default: true

Examples

PAL->NTSC conversion:

AVISource("PAL_clip.avi")              # Get clip
Bob(height=480)                        # Separate fields and interpolate them to full height.
BicubicResize(640,480)                 # Resize to NTSC square-pixel frame size.
ChangeFPS(60000, 1001)                 # Convert field rate to NTSC, by duplicating fields.
SeparateFields.SelectEvery(4,0,3)      # Undo Bob, even field first. Use SelectEvery(4,1,2) for odd field first.
Weave()                                # Finish undoing Bob.

The effect is similar to 3-2 telecine pull down. Regular viewers of PAL material may notice a motion stutter that viewers of NTSC material readily ignore as for telecined film.

ConvertFPS

Attempts to convert the frame rate without dropping or inserting frames, providing a smooth conversion with results similar to those of standalone converter boxes. The output will have (almost) the same duration as clip, but the number of frames will change proportional to the ratio of target and source frame rates.

Frame rate conversion is inherently difficult. This filter implements two common methods used by commercial Prosumer-level converter systems. The results are typically quite good. More sophisticated systems employ motion interpolation algorithms, which are difficult to get right, but, if done right, do yield superior results.

Footage converted with this filter should not be converted again. Blurriness builds up quickly in subsequent generations.

The audio data is not touched by this filter. Audio will remain synchronized, although the length of the audio data may slightly differ from that of the video data after the conversion. This is because the output can only contain an integer number of frames. This effect will be more pronounced for shorter clips. The difference in length should be ignored.

ConvertFPS can be called 4 different ways, as documented below. Not all parameter values are checked for sanity.

Syntax and Parameters

ConvertFPS (clip1, clip2, int "zone", int "vbi")
ConvertFPS (clip, float new_rate, int "zone", int "vbi")
ConvertFPS (clip, int numerator, int denominator, int "zone", int "vbi")
ConvertFPS (clip, string preset, int "zone", int "vbi")
clip, clip1

Source clip; all color formats supported.

clip2

If supplied, the new framerate is taken from this clip.

new_rate
Target frame rate. Can be integer or floating point number.
In Blend mode, new_rate must be at least 2/3 (66.7%) of the source frame rate, or an error will occur. This is to prevent frame skipping. If you need to slow down the frame rate more than that, use Switch mode.
Due to the way frame rates are stored, new_rate must be converted to the closest ratio of 32-bit signed integers, eg, 33.3333 → 329833/9895 (33.3332996)
numerator, denominator

If supplied, the new framerate is set to numerator divided by denominator. The same restrictions apply as for new_rate. If only the numerator is given, denominator defaults to 1.

preset

If supplied, the new framerate is taken from a set of standard rates, as listed under AssumeFPS.

zone

If specified, puts the filter into Switch mode. Must be greater or equal to zero. If zero, the filter will perform a hard switch, that is, it will immediately display the next frame below the switch line. If greater than zero, specifies the height (in lines) of the transition zone, where one frame is gradually blended into the next. zone=80 yields good results for full-size video (480/576 active lines). The transition is done in the same way as in PeculiarBlend. Zone must be less or equal than the number of lines of the target frame that correspond to the duration of the source frame. This is typically 5/6 or 6/5 of the target frame height, that is, a few hundred lines. An error occurs if a larger value is chosen.

vbi

If specified in Switch mode, specifies that the filter should apply a timing correction for the vertical blanking interval (VBI). Integer number greater than zero, indicating the height of the VBI of the target frames, in lines. Typically vbi=49 for PAL and vbi=45 for NTSC, but these values are not critical. Ignored in Blend mode.

Modes

The filter has two operating modes. If the optional argument zone is not present, it will blend adjacent video frames, weighted by a blend factor proportional to the frames' relative timing (Blend mode). If zone is present, it will switch from one video frame to the next (Switch mode) whenever a new source frame begins – usually somewhere in the middle of a target frame. Switch mode assumes that the output will be shown on a TV where each frame is scanned from top to bottom. The parameter zone specifies the height of the transition region in which the current frame will be blended into the next.

  • Blend mode will cause visible, although slight, blurring of motion. This is a typical artifact of frame rate conversion and can be seen on commercial video tapes and TV programs as well. When working with interlaced video, it is important to let the filter operate on individual fields, not on the interlaced frames. (see Examples below.)

  • Switch mode is an attempt to avoid motion blurring, but comes at the expense of slight flicker and motion artifacts. Horizontal and vertical pans may show a slight wobble. Still frames from this conversion show "broken" or "bent" vertical lines in moving scenes. Scene transitions may occur in the middle of a frame. Nevertheless, the results do look less blurry than in Blend mode.

Neither mode is perfect. Which one to choose depends on personal preference and on the footage to be converted. Switch mode is probably only suitable if the output will be shown on a TV, not on a computer screen.

Examples

NTSC->PAL conversion:

AviSource("NTSC_clip.avi")             # Get clip
Bob(height=576)                        # Separate fields and interpolate them to full height.
BicubicResize(768,576)                 # Resize to PAL square-pixel frame size.
ConvertFPS(50)                         # Convert field rate to PAL, using Blend mode.
SeparateFields.SelectEvery(4,0,3)      # Undo Bob, even field first. Use SelectEvery(4,1,2) for odd field first.
Weave()                                # Finish undoing Bob.

This example will also work with frame-based NTSC material, even with telecined film (movies).

For film material, however, you will get better results by using an inverse-telecine filter and speeding up the frame rate from 23.976 to 25fps.

Changelog

Version

Changes

AviSynth+ r2632

ConvertFPS: added 10-32bits support.

AviSynth 2.5.7
AssumeFPS, ChangeFPS, ConvertFPS: added preset option.
ConvertFPS: YV12 and RGB support and fixed blending ratio.
AssumeFPS, ChangeFPS, ConvertFPS: changed framerate behaviour, see below.
From v2.57, the behaviour with respect to the framerateis a bit changed. The main issue is that users are allowed to specify the framerate as float, but the NTSC (FILM and Video) and PAL standards require ratios as framerate. Besides this AviSynth exports the framerate as a ratio, so when specifying a float, it will be converted to a ratio. The ratios of the standards are given by 24000/1001 for 23.976 (FILM) and 30000/1001 for 29.97(Video). When specifying these floats, they are exported by AviSynth as ratios, but not as the standard ratios. One of the reasons for this is, that those floats are approximations (remember that 24000/1001 = 23.9760239760...), so how should AviSynth know how to choose the correct ratio? In order to overcome this issue, the user can use AssumeFPS(24000,1001) or simply AssumeFPS("ntsc_film").
Another problem is that in v2.56 and older, the converted floats were exported with 64 bit precision, resulting in very large numerators and denominators, making some players crash. To overcome this, a smart float-ratio is added internally, and the framerates are approximated accurately by ratios of small numbers. For example, AssumeFPS(23.976) is converted to AssumeFPS(2997, 125) as can be checked with Info.

AviSynth 2.5.6
ChangeFPS and ConvertFPS: added clip2 option.
Added AssumeScaledFPS filter.

AviSynth 2.5.5

AssumeFPS: added clip2 option.

AviSynth 2.5.4

ChangeFPS: added linear=true/false option.

AviSynth 2.0.5

ChangeFPS: Up to v2.05, the video gets truncated or filled up to preserve playback speed and play time (the number of frames was not changed). In later versions, the behaviour has been changed and the number of frames is increased or decreased as in ConvertFPS.

$Date: 2022/07/30 14:45:27 $