File Size and Duration
Average bitrate and running time provide a practical estimate of a media file's size.
Start with the streams you intend to store. For a two-hour film, suppose video averages 10 Mb/s and each of two soundtracks averages 384 kb/s.
bytes = average bits per second × seconds ÷ 8
There are 7,200 seconds in two hours. The video therefore contributes 10,000,000 × 7,200 ÷ 8 = 9,000,000,000 bytes.
| Stored component | Average rate | Bytes over two hours | Decimal GB |
|---|---|---|---|
| Video | 10 Mb/s | 9,000,000,000 | 9.0000 |
| Audio 1 | 384 kb/s | 345,600,000 | 0.3456 |
| Audio 2 | 384 kb/s | 345,600,000 | 0.3456 |
| Streams combined | 10.768 Mb/s | 9,691,200,000 | 9.6912 |
Container structures, subtitles, attachments, and tags add their own bytes. An embedded image adds storage without adding running time. The stream sum estimates the largest contributions; an overall file average already includes all the stored bytes used in its calculation.
Work the relationship in either direction
If a finished two-hour file is exactly 9.8 billion bytes, its overall average is:
9,800,000,000 × 8 ÷ 7,200 = approximately 10.889 Mb/s
A file half as long at that same size has twice the overall average. A larger size can thus mean a longer presentation, more tracks, or more data per second; the division tells you which of these quantities you are comparing.
Decimal and binary units change the displayed number, not the underlying bytes. The 9.6912 GB stream sum is about 9.026 GiB. Always establish the units before comparing an encoder estimate with a file browser's display.
When the calculation exposes another problem
Some inspection tools obtain overall bitrate by dividing file size by reported duration. If a two-hour source is mistakenly reported as one hour, that derived bitrate doubles. Repeating the same calculation cannot independently confirm either value.
That is useful when Emby or an inspection report shows a surprising rate. Compare the duration evidence with the expected presentation and track timestamps. A damaged or incomplete file can have intact headers yet a different amount of actual media.
For planning a target size, choose the duration and complete data budget first. For examining an existing file, use the measured size and a trustworthy duration. Local variation affects delivery and buffering, while this calculation accounts for the total.