How to get current frame number in AviSynth?

[zee944]

Can anyone tell me how can I have the current frame number in AviSynth?

Within ScriptClip command, I can display it such as:

ScriptClip("subtitle(string(current_frame))")

...but AviSynth doesn't recognize a stand-alone 'current_frame'.

What I actually want to do is to increase saturation from zero to maximum during playback. The first frame is B&W, the last has the original saturation. If 'current_frame' would work, my line would look like this:

Tweak(sat=(current_frame/FrameCount)*1.00)

Could anybody help?

[Sagekilla]

Try animate:

ColorBars().ConvertToYV12()
src = last
start_frame = 0
end_frame = 99

src.Animate(start_frame,end_frame, "Tweak", 0,0.0, 0,1.0)

[J_Darnley]

Cast the frames to floats so that you don't use integer division and then put it all in a ScriptClip().
ScriptClip( "Tweak( sat=( float(current_frame)/float(FrameCount) )*1.0 )" )

[Gavino]

Originally Posted by zee944

...but AviSynth doesn't recognize a stand-alone 'current_frame'

current_frame is only visible within the run-time environment provided by filters such as ScriptClip.

Hence J_Darnley's solution is closest to your original idea (though clearly the 1.0 is redundant). However, for a case like this, I prefer Sagekilla's approach with Animate.

[IanB]

MergeChroma(FadeIn0(100))

[zee944]

Originally Posted by J_Darnley

ScriptClip( "Tweak( sat=( float(current_frame)/float(FrameCount) )*1.0 )" )

Thank you for all of you. This one worked damn perfectly, so I didn't even try the others!

[stickboy]

The other approaches are better...

[Sagekilla]

If you look at it speedwise, I believe IanB's would be the fastest. A copy of the chroma channel is faster than multiplying the saturation by some float (which is calculated based on what frame you're on and the total frame count, another calculation) I think.


I think all methods are fast enough that decoding is slower still, though.

[stickboy]

IanB's is also the most AviSynth-like.

The ScriptClip way encourages wrong thinking.

[Sagekilla]

Not to mention the most elegant for that matter, No need to futz around with worrying about types or anything. Just two function calls

[blausand]

To be honest, the absence of current_frame still really gets me down from time to time. And stickboy, i agree that all of these Scriptclip-solutions feel conceptually wrong whenever i hassle around with them.

look at this:

clp = AVISource("some.avi")
import("someNumberedStrings.txt")

index = ((current_frame+3) % 20) > 10 ? int(current_frame/20) : 0

topSlate = Eval("topslate_"+string(index, "%03d"))
bottomSlate = Eval("bottomslate_"+string(index, "%03d"))

subtitle(bottomSlate, align=2)
subtitle(topSlate, align=8)

I need some math-munging to evaluate the right slates. Then i tried to put everything in a function.
Both approaches yield the error: "I don't know what 'current_frame' is."

I also tried to relate current_frame to a clip: clp.current_frame, and that yields:
"There's no function named 'current_frame' "
And even wrapping everything in FrameEvaluates didn't solve anything.
Is there no workaround to get a current_frame integer based on a specified clip?

[Gavino]

Originally Posted by blausand

Is there no workaround to get a current_frame integer based on a specified clip?

It normally makes no sense to talk of the 'current' frame of a clip because Avisynth deals in complete clips, not individual frames.

The only place it does makes sense is inside a "run-time" script as processed by ScriptClip, as these are (re-)evaluated for every frame of their surrounding 'normal' script. Even here, the processing required can most often be done without caring what the actual frame number is.

See here for an example of how to solve your problem using ConditionalReader.

[stickboy]

Originally Posted by blausand

To be honest, the absence of current_frame still really gets me down from time to time. And stickboy, i agree that all of these Scriptclip-solutions feel conceptually wrong whenever i hassle around with them.

...
subtitle(bottomSlate, align=2)
subtitle(topSlate, align=8)

I need some math-munging to evaluate the right slates. Then i tried to put everything in a function.
Both approaches yield the error: "I don't know what 'current_frame' is."

I also tried to relate current_frame to a clip: clp.current_frame, and that yields:
"There's no function named 'current_frame' "
And even wrapping everything in FrameEvaluates didn't solve anything.
Is there no workaround to get a current_frame integer based on a specified clip?

Why do you need current_frame at all? Why not use ApplyRange?

[Gavino]

Originally Posted by stickboy

Why do you need current_frame at all? Why not use ApplyRange?

ApplyRange won't do it easily because he wants the thing to be dynamic.
But it could be done with Animate something like this:

function DoTitles(clip c, int index) {
  topSlate = Eval("topslate_"+string(index, "%03d"))
  bottomSlate = Eval("bottomslate_"+string(index, "%03d"))
  c
  subtitle(bottomSlate, align=2)
  subtitle(topSlate, align=8)
}

import("someNumberedStrings.txt") # needs to declare strings global
nTitles = ... # no of titles 
start = ... #start frame
end = ... #end frame
clp = AVISource("some.avi")

Animate(clp, start, end, "DoTitles", 1, nTitles)

@blausand
Instead of thinking in terms of current_frame, it is usually better to use a built-in filter that produces a dynamic effect, eg Animate, FadeIn, Dissolve, etc.