In this part, we will tell you the details, or the logic, about how to calculate video file size. (Note: If you need to change the file size of a video, you may need one of the best video converters.)
Firstly, we need to know, or you may have known, that each video file consists of hundreds and thousands of images. And one image is called a frame in a video file, technically. So to answer the question, it seems that we need first to figure out how to calculate one frame (image).
Each frame or image consists of many pixels. And how many pixels exactly it has depends on its horizontal pixels and vertical pixels, or the resolution. For example, one 4K image with 4096 x 2160 resolution, then its total pixels are 8847360. I guess this is not hard to understand, right.
But the real question is how much storage one pixel takes up. If we know it, then the size of one frame equals that the size of one pixel times the resolution.
To figure out how much storage one pixel takes up, here is another knowledge point that we need to learn about. It is Bit Depth, or called Color Depth.
Bit Depth means the color information stored in one pixel. Only when one pixel stores some colors, then the image can show us a cat, a dog, a flower, or something else. The bigger the number of the bit depth, like 1-bit, 2-bit, 4-bit, 8-bit, 16-bit, etc. the more color information one pixel can store, more precisely the whole image would be described, and consequently more storage the image would take up.Why?
The color of each pixel is the combination of the three primary colors: red, green, and blue. Each primary color is often called a color channel and can have any range of intensity values specified by its bit depth. The bit depth for each primary color is termed the bits per channel. The bits per pixel (bpp) refers to the sum of the bits in all three color channels and represents the total colors available at each pixel. Here are some specific examples, which maybe help you understand those words above easily.
1-bit per channel has only two color options: often black and white, so it can only use one 0 and 1, or 1 bit.
2-bit per channel will have 22=4 colors, and it can use two 0's and 1's, or 2 bits.
4-bit per channel has 24=16 colors, and it can use four 0's and 1's, or 4 bits.
8-bit per channel has 28=256 colors, and it can use eight 0's and 1's, or 8 bits. This one is widely applied.
16-bit per channel has 216=65536 colors, and it can use sixteen 0's and 1's, or 16 bits.
24-bit per channel has 224=16777216 colors, or called true color, and it can use sixteen 0's and 1's, or 16 bits.
Now we have pretty much get the Bit Depth clear. And in the following content related to Bit Depth, we will take the 8-bit per channel as an example to help us.
And at this time, we can also calculate how much storage one frame, or one image will take up. The formula, which we have mentioned above, is,One frame size = Total number of pixels x the size of one pixel
Like we have said, we take the 4K resolution (4096 x 2160) and 8-bit per channel as examples. So for a 4K video file, the size of its one frame would be 4096 x 2160 x 8 = 70778880 bits.
Well, bits are less likely to see out there. It would be much better to convert into megabytes (MB).
1 megabytes = 1024 kilobytes;
1 kilobyte = 1024 bytes;
1 byte = 8 bits;
So 70778880 bits = 70778880/(8 x 1024 x 1024) MB = 8.4375 MB. That is to say, for 4K video file with 8-bit Bit Depth, the size of one frame is 8.4375 MB.
Now we can answer the question of how to calculate video file size, and here is the video file size formula,Video file size = Time (second) x Frames per Second (FPS) x Pixels per Frame (Resolution) x Bit Depth
Please let me explain to you the meaning of each item in this formula. Time refers to how long your video is; Frame per Second, or called FPS, means how many frames will be played per one second for this video; Pixel per Frame, or the Resolution, and Bit Depth have been talked about above.
Imagine there is a 4K video with 30 minutes, 60FPS, 4096 x 2160 pixels, and 8-bit Bit Depth, then its size would be (in MB),
30 x 60 x 60 x 4096 x 2160 x 8 ÷ 8 ÷ 1024 ÷ 1024 = 911250 MB;
OK, let's convert it to gigabyte (G), and it would be,
911250 ÷ 1024 = 889.89GB.
This is kind of scary. Probably many of you even would not believe this number, right? But it is true.
If we want to transfer such a 4K video to one of our friends, and the uploading internet speed is 10M, it would take us about 25 hours.
Seriously, this is very inconvenient for information sharing. So the engineers came up with the solution - encoding the video files. The main purpose of video encoding is reducing its size. There are many ways to encode a video file. If you are interested in this, you can refer to this guide from Wikipedia. Each encoding method comes with its unique compression algorithm and ratio. Besides, we also need to know that even if different devices, for example iPhone X and Android Pixel, use the same encoding way to compress a same video file, the final size probably would be not same.
So considering its complexity, we will not continue with how to calculate encoded video file. But this online tool on this page can work it out easily.
Honestly, sometimes, even though the video file has been encoded, it is still too large. At this time, if you plan to make it smaller, we also have some other ways you can try.
And the detailed methods are all listed in this guide (Best Video Size Reducer - Compress Video File Size by up to 90% with No Quality Loss). You can check them all there.
Technically, if this 4K movie or video is not compressed or encoded, then we can find the answer from the words above.
Presumably, this 4K file is with 4096 x 2160 pixels, 30-minute long, 60FPS, and 8-bit Bit Depth, then it would be 889.89GB big.
While, if this 4K movie is encoded or compressed (like when we shoot a 4K video with iPhone X, the file is encoded by the Apple's way), we can use this online video size calculator to help you.
Now we we have a 64GB card or other storage, and want to know the length of the 4K video it can hold, right?
Presumably, this 4K file is still with 4096 x 2160 pixels, 60FPS, and 8-bit Bit Depth, then 64GB storage can hold a uncompressed 2-minute long 4K video, more or less. If it has been encoded, please check this 4K video file calculator to help you.
Similar to the last question, a 128GB card or other storage can hold a uncompressed 4-minute long 4K video, more or less, if the file is with 4096 x 2160 pixels, 60FPS, and 8-bit Bit Depth.
Still using the data above, 1-minute-long 4K video would be 30GB in size.
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