Whether preparing videos for web landing pages, Discord messaging, or email attachments, raw camera footage is far too heavy. Understanding bitrate control gives you predictable, high-quality results.
The 3 Factors That Determine Video File Size
A video file size is simply: `File Size = (Video Bitrate + Audio Bitrate) × Duration`. Frame resolution (such as 1080p or 4K) does not directly determine file size; rather, it determines how many pixels the bitrate is spread across.
How to Calculate the Target Bitrate for Limits
If you need a 60-second video to stay under a 20MB email cap:
- 20MB = 160 Megabits = 160,000 Kilobits.
- Divide 160,000 Kb by 60 seconds = ~2,600 Kbps total bandwidth.
- Allocate 128 Kbps for audio and ~2,400 Kbps for video.
Codecs: H.264 vs H.265 vs VP9
H.264 (AVC) remains the most universally compatible video codec in the world, playing natively on virtually every television, browser, and smartphone. Modern codecs like VP9 and AV1 offer 30% higher compression efficiency at equivalent bitrates.
How to Compress a Video to 10 MB
The same arithmetic tells you what 10 MB can hold. 10 MB is 80 megabits, so a 60-second clip gets about 1,300 Kbps in total: roughly 128 Kbps for audio and 1,200 Kbps for video, which looks clean at 720p. A five-minute recording gets about 270 Kbps in total, which is only watchable at 480p or below.
In PDFixel, switch the Video Compressor to Target File Size and tap the 10 MB chip; the encoder works out the bitrate from the video’s length for you.
- Trim first. Every second you cut is bitrate handed back to the part you keep.
- Lower the resolution. 720p or 480p at a healthy bitrate looks better than 1080p starved of one.
- Drop the audio track if the video does not need sound. That frees the whole audio share for the picture.
How to Compress a Video for Discord
Discord’s free upload limit is 20 MB. Nitro Basic raises it to 50 MB and Nitro to 500 MB. The Video Compressor’s Discord Free (20 MB) preset aims a little under the free limit at 720p and 30 fps; with Nitro, set your own number in Target File Size.
If the clip is long, trim it to the moment you want to share before compressing. Fitting two minutes into 20 MB is easy, and fitting twenty minutes into it is not.
Compressing a Video for Instagram or TikTok
Both apps re-compress every video they receive, so the goal is not the smallest possible file but a clean 1080p source that survives that second pass. The Instagram / TikTok (1080p) preset encodes at 1080p and 30 fps for exactly that.
Heavy compression before the upload stacks the platform’s artifacts on top of your own, which is why a reel that looked fine on your phone can come out blocky. If an upload is refused for size, lower the target gradually rather than all at once.
Compressing Videos Directly in Your Browser
Using WebAssembly video encoders that run inside the browser, PDFixel allows you to compress MP4 and WebM videos without waiting for gigabytes of footage to upload to remote servers. Encoding happens on your own CPU, so a longer clip on a modest machine will take longer than it would on a dedicated server — the trade you get in return is that the footage never leaves your device.
Summary
By matching target bitrate to your video duration, you can reliably fit video clips into any file size constraint while keeping motion smooth and details clear.