How to calculate size of video file after encoding?

[vid83]

I am convertin a miniDV NTSC video into .mp4 H264.
I have to wait 30 minutes for the video to encode to see that the final file size will be.
This can be time consuming.
Is there an online calculator that will allow me to select the file type, codec, bitrate, duration and let it calculate approximately how big my files will be?

[minidv2dvd]

the formula is the same for any type video. duration x bitrate = file size

[jagabo]

If you use bitrate based encoding the file size is simply:

file size = bitrate * running time

Where bitrate is the sum of audio and video bitrates. Keep in mind you need to adjust for bits/byte and watch your units.

For example 1 hour with a total bitrate of 8000 kbps; 1 hour is 3600 seconds so:

file size = 8000 kbps * 3600 seconds
file size = 28,800,000 k bits

there are 8 bits per byte so:

file size = 28,800,000 k bits / 8
file size = 3,600,000 k Bytes
file size = 3.6 GB

Many bitrate calculators can do this for you.

[PuzZLeR]

For H.264, if you're using x264, and quantizers, or constant quality encoding (such as CRF, which is highly recommended for x264 encoding) you will not know in advance how big your final file size will be. It will give you the minimum bitrate possible for the quality you ask of it, and that minimum is highly variable scene by scene.

Not sure of your level, but if that's the case, and you know some AviSynth, run a test encode and just add this line at the end of your script:

SelectRangeEvery(1000,10,0)

This is using "inference", which encodes 1% of the movie (10 frames every 1000 starting at 0). The bitrate of this combined “movie” should give you an idea of how big the final file will be.

I find using 2.5% much more accurate, and still a quick test encode. Try:

SelectRangeEvery(1000,25,0)

The higher the percentage, the closer to the empirical result. (A limiting approximation...)

If the calculus or statistics class was too much for you, just stick with arithmetic and use 2-pass encoding and fill in the appropriate bitrate with a bitrate calculator instead as mentioned above. I personally prefer an optimized one pass solution if using x264 given its long encoding times.