Inspiring

Question

sHow to calculate duration of audios? Does it have anything with encoding, type and frame rates?

Forum|Forum|2 years ago
December 24, 2023
5 replies
1732 views

Hello,

I am having a problem because When I calculate duration of an audio with external tools, I find a certain value, but when I open it on Premiere Pro, I get another value.

For example, I have an audio clip that has a duration of 2517 ms = 2s + 15.51 frames.

But inside Premire Pro it shows 00:00:00:02:12 = 2 s + 12 frames ~ = 2 s + 12x33.33 ms= 2399 ms

I would like to achieve 99%+ precision.

Another example was correct:

An audio calculated to have 3880 ms = 3s + 880 ms = 00:00:03:26 ~

It has the same inside PPRO.

But the first example was an "accelerated" audio (through a process that I am not sure about yet),

My question:

how can I ensure the length of audios are always the same, can I modify somethign about my files to make them always "compatible" with PPRO? Maybe some encoding or something about frames etc?

I guess I am looking at tools that modify my audios to make them display same lengths weither they are shown inside PPRO or calculared with external tools.

The accelerated Audio showed wrong values, and it's a problem for me.

(Ps. the duration is calcualted on the already accelerated audio, it's not a prediction).

Thanks

This topic has been closed for replies.

R

Richard M Knight

Community Expert

I've just had a play with some of the Premiere settings and it seems when importing any audio only file that does not have any timecode metadata, the timecode that Premiere uses for that file is determined by the Interminate Media Timebase setting in the prefs.

Any audio that is added to a sequence and double clicked to open in the source monitor will then assume the framerate of that sequence.

R Neil Haugen

Legend

Video framerates are not exactly what they seem ... 29.97fps is not 30fps, but many devices that record in wha they say is "30fps" actually record at 29.97.

Many devices that record at "24fps" are actually recording in 23.976. But some are actually in 24fps, solid.

And then ... there's drop-frame versus non-drop frame.

It's complicated ...

Everyone's mileage always varies ...

R

Richard M Knight

Community Expert

Do your calculations change if you select 'Audio Time Units' for the timecode display option.

Bed30321077z973Author

Inspiring

They become exactly what I had predicted!

Very interesting (516 is close to 517)

My question is why would Premiere PRO, display 516 ms as :12 (12 frames), instead of 15 frames ????

R

Richard M Knight

Community Expert

You must remember that audio only files do not have a framerate, only a sample rate so I'm not sure what frame timebase it uses for these audio files.

Remote Index

Inspiring

Hello Bed etc.,

You have not given enough information about your question.

"For example, I have an audio clip that has a duration of 2517 ms = 2s + 15.51 frames."

What is the frame rate you are using in this calculation?

"But inside Premire Pro it shows 00:00:00:02:12 = 2 s + 12 frames ~ = 2 s + 12x33.33 ms= 2399 ms"

What is the timebase (framerate) you are basing this calculation on?

Frames in timebases of 23.976, 29.97, 25, 30, 60 will all yeild different results. Without specifying your timebase it not possible to go further with your questions. (eg. 12 frames out of 24 is half a second. 12 frames out of 30 is 2/5ths. 12 frames out of 29.97fps is a bit more than 2/5ths).

Or to restate it simply: a frame does not have a universal duration, it has a duration in relation to the frame rate.

R.

Bed30321077z973Author

Inspiring

Hello @Remote Index ,

Thanks for the answer, let me clarify it for you,

Every calculation was either:

1) Calculate duration of an audio BEFORE importing it to PPRO (using an external tool)

2) Then use PPRO timebase as a base to "predict" what will the audio show in PPRO.

3) The base is 1000 ms = 30 frames. But my confusion is: will that work with ANY audio file I have? And I am starting to think this might not be the case? (Mind you I don't know a lot of about audios and their properties)

4) I noticed that my calculation of 2517 ms = for a clip that had been accelerated before being imported => did not give me the right duration inside PPRO (meaning the rule 1000 ms = 30 frames, did not work out)

5) Then I noticed that for another clip that had not been accelerated, the rule 1000 ms = 30 frames, worked fine for me and 3880 ms gave me exaclty the duration PPRO would show once the file imported.

My question was then: why? And Can I modity the first file to make it always have correction predictions?

I want that whenever I calculate the duration of an audio (before importing it), then I will obtain ALWAYS a duration corresponding to the rule 1000 ms = 30 frames.

I am starting to think that PPRO does not care about the duration of an audio as much as about the properties of the audio,

and something is telling me that my first audio has some properties modified which made it :

A) show a certain duration

B) But in reality it was a false duration.

OR MAYBE, the external tool I used to calcualte duration of the audios, does not "know" how to access files properties and got "tricked" into giving a false duration (meaning that tool calcualted 2517 ms and was wrong, whereas PPRO is always right about the duration calculation).

So what would make my first clip make other tools get its duration wrong? And how can I modify audio files to always be "reliable" and never makign these tools wrong.

And yes yes, I need to calculate my audios duration before importing them to PPRO.

Thanks

Remote Index

Inspiring

Hello Bed etc.,

"Calculate duration of an audio BEFORE importing it to PPRO (using an external tool)"

As you have not said much about what or how you are doing, there is little I can say here. But I would suggest checking whether you are calculating duration or if you are identifying the end of the file. These two values may be different (in the same way that elsewhere it has been pointed out that "duration" and "end point" are differnt in Premiere Pro.

"The base is 1000 ms = 30 frames"

Why is this your base assumption? It is not necessarily correct. Premiere Pro will assigns a frame rate to audio for display purposes. As Richard M Knight has pointed out, if you load audio in the source monitor, PPro uses the "indeterminate media timebase". If you have this set to "30" (not 29.97) then your above assumption should be correct. If you use audio in a sequence, then it will be handled per the sequence frame rate. If this is 30 (not 29.97) then your above assumption is correct.

(I have not been able to confirm if Premiere Pro handle timecode metadata on audio in a more direct manner but this should not affect any of your questions as I don't believe you're using audio with timecode.)

"... a clip that had been accelerated before being imported ..."

You are vague about what you mean by “accelerated”. This could mean many things, but the way you have referred to it, it implies some sort of meta-data driven process, but I am sceptical about this. (There are ways of changing the way a recorded file plays back, but I am not certain that’s what you are doing.) On the other hand, if you’ve modified audio and exported the result in another application, then the resulting file has a duration, sample rate, bit depth, maybe timecode etc. regardless of any source file you are referring to. To be more precise, either explain your mysterious “acceleration” process if it is metadata driven or simply refer to a source file (with its given duration etc.)

Finally, I will once again remind you that audio can have durations of partial frames in Premiere Pro, so the frame units that you are using will be approximations (to within the nearest frame). Using "audio units" (which in Premiere Pro are calculated and displayed as samples) will be more accurate.

R.

Ann Bens

Community Expert

When the audio is linked to video, all calculations are done in frames.

Bed30321077z973Author

Inspiring

Hello @Ann Bens , This audio is independant, not from a video.

I imported this audio of few seconds and had it "accelerated" BEFORE importing it to PPRO.

Then I used an external tool to calculate its duration, and it gave me : 2517 ms,

Then I tried to convert that duration to PPRO usuation durations, which is 1000 ms = 30 frames, right?

(So that gave me a prediction of 2 sec + 15 frames, but instead I see that PPRO is saying that this audio is only 2 s and 12 frames)

My question is: how can I, before importing, make sure that my audios will always correspond to PPRO standards, and get the same "properties" per se, that will allow it (the clip) to get a correct prediction of its duration corresponding to what PPRO will show?

Mind you I don't know a lot about audios files and their properties. I am not sure what I should do in terme of "conversion, encoding..etc?" to the film ..

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