How to shorten playing time of MP4 file?

[ConverterCrazy]

Hello,

I want to shorten the playing time of an MP4 file [duration=68 minutes]. The contents are not that long but the speakers speak in a slow pace. If I increase playing speed to 1.2, the video plays well and audio is fine too.

Can I do something to make video play faster without changing playing speed in PotPlayer?

Thanks.

[ProWo]

You could increase the audio pitch without change the video.
This can be done with clever Ffmpeg-GUI.

[ConverterCrazy]

You could increase the audio pitch without change the video.
This can be done with clever Ffmpeg-GUI.

Thanks.

One question:
Will it not put video audio out of sync?

[ProWo]

No

[ProWo]

Download the newest beta here:
https://files.videohelp.com/u/292773/clever_ffmpeg_gui_newest_beta.7z

Then load your mp4, click main, click Convert Audio stream, Continue, type 1.2 in the coefficient field, select pitch only below, leave all other settings as they are, click convert.


[Attachment 61385 - Click to enlarge]

When done, click Multiplex, all necessary streams are already loaded (the new created audio stream is shown in green color), deselect the old audio stream, select mp4 as container (if it is not already selected), click Multiplex.


[Attachment 61386 - Click to enlarge]

All done!

[ConverterCrazy]

Download the newest beta here:
https://files.videohelp.com/u/292773/clever_ffmpeg_gui_newest_beta.7z
…
All done!

Thanks for the step-by-step guide.

It has changed male voices into female voices but the duration has remained 67 minutes!
I want to cut down the duration by a factor of 1.2 or 1.25.

Is it possible?

[ProWo]

Thanks for the step-by-step guide.
It has changed male voices into female voices but the duration has remained 67 minutes!
I want to cut down the duration by a factor of 1.2 or 1.25.
Is it possible?

To shorten the video, you need to recode it.
As a result, you will probably end up with a non-compliant framerate.
The video may then only play on the computer.
But it is possible.
To be more precise, we need more information.
Post a mediainfo report (text mode) here.

[ConverterCrazy]

Here it is:

General
Complete name : C:\Working Folder\Video\Understanding No Blasphemy.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 202 MiB
Duration : 1 h 7 min
Overall bit rate : 416 kb/s
Description :
Writing application : Lavf59.6.100

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L2.1
Format settings : CABAC / 1 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 1 frame
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1 h 7 min
Bit rate : 281 kb/s
Width : 426 pixels
Height : 240 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 30.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.092
Stream size : 136 MiB (68%)
Title : ISO Media file produced by Google Inc. Created on: 10/19/2021.
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 1 h 7 min
Bit rate mode : Constant
Bit rate : 128 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 62.0 MiB (31%)
Title : ISO Media file produced by Google Inc.
Language : English
Default : Yes
Alternate group : 1


As seen here, the duration is 67 minutes which I want to reduce to 50 minutes.

[ProWo]

The video currently has a frame rate of 30.
If you want to shorten the video by a factor of 1.3, it must be encoded at 39fps.
This shortens the time from 67 min to 51.53 min.
To achieve this, load your video, click main, click convert video stream, click continue, enter all data as on the picture, click convert.


[Attachment 61387 - Click to enlarge]

If done, click Convert Audio stream, Continue, type 1.3 in the coefficient field, select lenght only below, leave all other settings as they are, click convert.


[Attachment 61388 - Click to enlarge]

Mux afterwards as indicated above.

[ConverterCrazy]

Thanks.

Will do ASAP.

[ConverterCrazy]

The video currently has a frame rate of 30.
If you want to shorten the video by a factor of 1.3, it must be encoded at 39fps.
This shortens the time from 67 min to 51.53 min.
To achieve this, load your video, click main, click convert video stream, click continue, enter all data as on the picture, click convert.

If done, click Convert Audio stream, Continue, type 1.3 in the coefficient field, select lenght only below, leave all other settings as they are, click convert.

Mux afterwards as indicated above.

Thanks a ton.

[ConverterCrazy]

The video currently has a frame rate of 30.
If you want to shorten the video by a factor of 1.3, it must be encoded at 39fps.
This shortens the time from 67 min to 51.53 min.
To achieve this, load your video, click main, click convert video stream, click continue, enter all data as on the picture, click convert.


[Attachment 61387 - Click to enlarge]

If done, click Convert Audio stream, Continue, type 1.3 in the coefficient field, select lenght only below, leave all other settings as they are, click convert.


[Attachment 61388 - Click to enlarge]

Mux afterwards as indicated above.

I updated the software to latest version 3.1.1 and the ffmpeg to the recommended version.

Now, the option in the image [Change length] has vanished.

Reverting to older version 2.8.8 doesn't work.

What can be done now?

[ProWo]

I updated the software to latest version 3.1.1 and the ffmpeg to the recommended version.
Now, the option in the image [Change length] has vanished.
Reverting to older version 2.8.8 doesn't work.
What can be done now?

You mean Change Length in the Video encode section?
The checkbox is only displayed if the target FPS is different from the source FPS.
Otherwise it makes no sense.


[Attachment 71563 - Click to enlarge]

[ConverterCrazy]

Thanks

[ConverterCrazy]

Hello,

I tried to slow down the playing speed from 30fps to 23fps.
All went well except for flicker in the output video.

Is there a solution?

[rgr]

Thanks for the step-by-step guide.
It has changed male voices into female voices but the duration has remained 67 minutes!
I want to cut down the duration by a factor of 1.2 or 1.25.
Is it possible?

To shorten the video, you need to recode it.
As a result, you will probably end up with a non-compliant framerate.
The video may then only play on the computer.

No need to recode the video. It is enough to change the framerate from 30 to 36 (+20%) in the video stream and recode the audio track.

This command changes 25fps to 23.974fps -- just need to change the values:

ffmpeg -itsscale 1.0427083 -i input.mp4 -vcodec copy -filter:a "atempo=0.959041" output.mp4

for example:

ffmpeg -itsscale 0.8 -i input.mp4 -vcodec copy -filter:a "atempo=1.2" output.mp4

[Selur]

as a side note: remuxing to mkv an using the 'strecth by' function in mkvtoolnix gui might also be a solution,... (and doesn't require reencoding)