Looking for method to resize large video down to certain file size.

[Rytron]

Hi.

Is it possible to resize a video of e.g. 1.3GB to about 900MB via a terminal command or GUI way?

For example, I'd like the command to figure out the proper aspect ration and bit quality in order to reduce the video size down to 900MB.

Thanks.

[SeijiSensei]

You can do it with ffmpeg, but it takes some work: https://trac.ffmpeg.org/wiki/Encode/H.264

[Rytron]

You can do it with ffmpeg, but it takes some work: https://trac.ffmpeg.org/wiki/Encode/H.264

Hi SeijiSensei.

Those command in your link look very tricky.

I may just stick with commands such as these:

• ffmpeg -i input.mp4 -vf scale=720:576 output.mp4
• ffmpeg -i input.mkv -vf scale=576:-1 output_576.mkv
• ffmpeg -i input.mkv -vf scale=-1:720 output_720.mkv
• ffmpeg -i input.mp4 -vf scale=iw/2:-1 output.mp4

[FakeOutdoorsman]

See the Two-pass example in the link provided by SeijiSensei:

https://trac.ffmpeg.org/wiki/Encode/H.264#twopass

Using two-pass method can allow you to achieve a desired output file size. (In the vast majority of all other cases, and if file size is not a priority, I recommend just using single pass with -crf).

If you don't feel like doing the math you can use a simple bitrate calculator. You just need to tell it the duration and the desired output file size.

Example if your input is 1 hour long and you want an output of approximately 900 megabytes:

ffmpeg -y -i input -c:v libx264 -preset slow -b:v 1918k -pass 1 -an -f mp4 /dev/null && \
ffmpeg -y -i input -c:v libx264 -preset slow -b:v 1918k -pass 2 -c:a libfdk_aac -b:a 128k -movflags +faststart output.mp4

I'm not sure why someone added audio encoding to the first pass example in the wiki, but I've never needed to do that, so I omitted it.

[Rytron]

See the Two-pass example in the link provided by SeijiSensei:

https://trac.ffmpeg.org/wiki/Encode/H.264#twopass

Using two-pass method can allow you to achieve a desired output file size. (In the vast majority of all other cases, and if file size is not a priority, I recommend just using single pass with -crf).

If you don't feel like doing the math you can use a simple bitrate calculator. You just need to tell it the duration and the desired output file size.

Example if your input is 1 hour long and you want an output of approximately 900 megabytes:

ffmpeg -y -i input -c:v libx264 -preset slow -b:v 1918k -pass 1 -an -f mp4 /dev/null && \
ffmpeg -y -i input -c:v libx264 -preset slow -b:v 1918k -pass 2 -c:a libfdk_aac -b:a 128k -movflags +faststart output.mp4

I'm not sure why someone added audio encoding to the first pass example in the wiki, but I've never needed to do that, so I omitted it.

Hi FakeOutdoorsman.

So I will try a video of about 2h50m. I want it reduced to 900 MB from 1.6 GB. Do I run 2 lines or 1?

[Rytron]

Are the values in my commands for kiloBytes or kiloBits?

[FakeOutdoorsman]

So I will try a video of about 2h50m. I want it reduced to 900 MB from 1.6 GB. Do I run 2 lines or 1?

You run two commands with two-pass encoding. Your commands may look something like this:

ffmpeg -y -i input -c:v libx264 -preset slow -b:v 592k -pass 1 -an -f mp4 /dev/null
ffmpeg    -i input -c:v libx264 -preset slow -b:v 592k -pass 2 -c:a libfdk_aac -b:a 128k -movflags +faststart output.mp4

Are the values in my commands for kiloBytes or kiloBits?

The -b option takes a value in bits, so you have to add a "k" to make it kilobits (as shown in the example above).

[Rytron]

@FakeOutdoorsman I went with Handbrake in the end. But I will keep your info for future reference. Cheers.