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Old 26th December 2020, 14:16   #1  |  Link
Perenista
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How can I change the fps from an audio?

Let's say I have AC3 audio tracks, MP3, or even DTS... if I wanted for example to change their fps from 23.976 to 24 or 24 > 23.976 fps what would be the best software (and way) to do this task, and with minimal loss?

Ideally I want these tracks to remain lossless, but of course if this change implies the other way around, which seems to be the obvious outcome, then I need to know how can this be achieved without hurting quality.

Note: the reason I need to do this change is because I have two recordings from the same content, but:

- If I try to sync the audio track from the 1st file into file #2, it will fail. That's because... let's say the difference between them is 10 seconds at the beginning.

So I could simply use MKVtoolnix to introduce a positive or negative delay of 10 seconds, and that would do the trick, right?

Not in this case. Doing that will only correct, say, the first 30 minutes. As the recording progresses, it will be out of sync again. So the 10 second difference now becomes 12 seconds if I forward into 1 hour.

That can only mean one thing: recording #1 is at a different fps from recording #2.

As such I need to do two things:

1) Change the fps from the audio track based on recording #1, to suit recording #2;

2) After that introduce a positive or negative delay, because recording #2 may have a different logo at the beginning, that accounts for the difference in runtime between the two.

Correcting only the beginning will not suffice if the fps is different. Since both recordings are the same, a different fps is what explains sync issues.

That's why I need a software to change the fps from the audio track extracted from my video.

Last edited by Perenista; 26th December 2020 at 14:19.
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Old 26th December 2020, 17:22   #2  |  Link
jlw_4049
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Quote:
Originally Posted by Perenista View Post
Let's say I have AC3 audio tracks, MP3, or even DTS... if I wanted for example to change their fps from 23.976 to 24 or 24 > 23.976 fps what would be the best software (and way) to do this task, and with minimal loss?

Ideally I want these tracks to remain lossless, but of course if this change implies the other way around, which seems to be the obvious outcome, then I need to know how can this be achieved without hurting quality.

Note: the reason I need to do this change is because I have two recordings from the same content, but:

- If I try to sync the audio track from the 1st file into file #2, it will fail. That's because... let's say the difference between them is 10 seconds at the beginning.

So I could simply use MKVtoolnix to introduce a positive or negative delay of 10 seconds, and that would do the trick, right?

Not in this case. Doing that will only correct, say, the first 30 minutes. As the recording progresses, it will be out of sync again. So the 10 second difference now becomes 12 seconds if I forward into 1 hour.

That can only mean one thing: recording #1 is at a different fps from recording #2.

As such I need to do two things:

1) Change the fps from the audio track based on recording #1, to suit recording #2;

2) After that introduce a positive or negative delay, because recording #2 may have a different logo at the beginning, that accounts for the difference in runtime between the two.

Correcting only the beginning will not suffice if the fps is different. Since both recordings are the same, a different fps is what explains sync issues.

That's why I need a software to change the fps from the audio track extracted from my video.
Try my software out

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Old 26th December 2020, 18:51   #3  |  Link
microchip8
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Audio doesn't have FPS. The equivalent to FPS would be Sample Rate
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Old 26th December 2020, 22:01   #4  |  Link
tebasuna51
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Like microchip8 say audio doesn't have FPS, maybe you need change the audio duration.
Of course it is not possible to do and remain lossless.

The best and easy option is change the video fps.
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Old 15th January 2021, 04:46   #5  |  Link
Perenista
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Quote:
Originally Posted by tebasuna51 View Post
Like microchip8 say audio doesn't have FPS, maybe you need change the audio duration.
Of course it is not possible to do and remain lossless.

The best and easy option is change the video fps.
So what would be the best software for this task?

Let's assume we have two AC3 files.

The first taken from a movie in which the disc was released at @24 fps

The 2nd with the same track, but another edition from the movie, at @23.976 fps

Two videos, however they don't match if I put AC3 number 2 into video 1.

So we will assume I want to adapt audio #2 which is from a 23.976 fps video source into video #1 at 24 fps...

What should I do? In the best way to keep the end result as close to being lossless as possible?
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Old 15th January 2021, 08:02   #6  |  Link
jlw_4049
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Quote:
Originally Posted by Perenista View Post
So what would be the best software for this task?

Let's assume we have two AC3 files.

The first taken from a movie in which the disc was released at @24 fps

The 2nd with the same track, but another edition from the movie, at @23.976 fps

Two videos, however they don't match if I put AC3 number 2 into video 1.

So we will assume I want to adapt audio #2 which is from a 23.976 fps video source into video #1 at 24 fps...

What should I do? In the best way to keep the end result as close to being lossless as possible?
My software or MeGui can do it

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Old 15th January 2021, 08:52   #7  |  Link
junh1024
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As tebasuna51 said, you can change the video FPS, and it will remain loss less. MKVtoolnix can do this. This choice is good, if you only want to keep 1 audio track.

If you want to keep both video tracks, you can use software like eac3to or FFMPEG to modify the audio. This is not lossless.
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Old 15th January 2021, 12:56   #8  |  Link
tebasuna51
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ffmpeg.exe -drc_scale 0 -i "audio2_23976.ac3" -af "atempo=1.001" -acodec ac3 -center_mixlev 0.707 -ab 448k "new24.ac3"

Put the same bitrate than original audio2.ac3

And mux with video 1 with MkvToolNix
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