128GB SD cards and flash drives are readily available and affordable. These SD cards are great for cameras when recording large amounts of video. It’s also great to use a 128GB USB drive to move video files quickly across devices. But just how many hours of video can you store on a 128GB storage device? Let’s dive in.
Factors That Affect Video File Size
Unfortunately, the answer to “how many hours of video can 128GB hold?” is a bit complicated. Videos are not all made the same. Here are the main factors that determine the file size of a video:
- Frame rate
- File format
- Color space
You may have realized we didn’t mention resolution. The actual resolution of a video file is not nearly as important as factors like frame rate and bitrate, so it’s not really a factor.
The frame rate of a video is how many frames per second are displayed. Movies are often 24 frames per second. Videos taken on a camera will probably be 30 or 60 frames per second. The difference between 30 and 60 can often be huge. There are other factors, but a 60 frames per second video could be double the size of a 30 frames per second video.
File Format and Compression
There are many file formats, and it changes depending on if you’re talking about video files recorded on your camera, or files exported from a video editor. Cameras tend to record in larger file formats to preserve quality, whereas exported files are often compressed. Compression does not always mean lower quality, but it can mean reduced file sizes. A compressed video will combine data of similar frames. This essentially means that certain frames are left out of the file. So, if you’re trying to store files recorded off of your camera, you might not be able to store as much video as if you were storing exported video projects. MP4 is commonly used for exported video files, while video from your camera could be in MOV format.
This number has a lot to do with file size. Bitrate is how many megabits per second are accessed when playing the video. This can factor into the quality of the video. The lower the bitrate, the more details are lost, even if the video is still in a high resolution. A ridiculously high bit rate is a waste, however, as it will increase file size while offering vastly diminishing returns on quality.
There is some easy math to determine how much video you can hold on a 128GB device if you know the bitrate of the video you’re recording (and assuming you don’t change any of the other factors mentioned here). 10Mbps is a common bitrate, and it makes the math easy. In order to convert to megabytes per second, we need to divide by 8. This will result in 1.25MBps. 128GB is 131,072MB. Now divide 131,072 by 1.25. This will leave you with 104,857 seconds of video. Divide again by 3600 (seconds in an hour) to convert from seconds to hours. This gives us a bit over 29 hours. So if your camera records at a constant bit rate of 10Mbps, you can count on being able to capture around 29 hours of video on your 128GB memory card.
Here is a simple math formula to help you out:
( (storage device size in MB) / ( Bitrate in Mbps / 8 ) ) / 3600 = Hours of video
Color space refers to a feature of professional video cameras. These cameras have the ability to shoot in log profiles, also called RAW video. These files are often massive, as they store significantly more color information than most other video files. This helps with color grading, as colorists will have more to work with. If you are recording RAW video files, don’t count on being able to store as many hours of video.
If you have more questions about storing video, we recommend you check out our article on the most reliable SD cards you can buy.