Bitrate
Bitrate measures how much encoded data represents each second of media.
Bitrate measures data against media time. At an average rate of 10 Mb/s, ten seconds of content accounts for 100 million bits, or 12.5 MB. It need not take ten seconds to download those bytes.
That distinction gives a transfer graph and a media report different meanings. A connection delivering 25 Mb/s can fetch ten seconds of this simplified content in four seconds. The player can then consume those stored bytes over the following ten seconds.
| Reported rate | The data being counted |
|---|---|
| Video bitrate | Encoded picture data |
| Audio bitrate | One encoded soundtrack |
| Overall file bitrate | All file bytes divided by presentation duration |
| Transfer rate | Data arriving per second of real elapsed time |
What is included in a movie's rate?
Imagine a file with 8 Mb/s of video and two 384 kb/s soundtracks. The streams total 8.768 Mb/s, before container structures and other content. A presentation that sends only the selected soundtrack has a different stream total: 8.384 Mb/s.
Whether the complete file or a selected set of tracks crosses a connection depends on delivery. This is why an Emby source's overall rate and its delivered stream rate can legitimately differ even without changing the video encoding.
Using an average
For storage, multiply the average by duration and divide by eight to change bits to bytes. Ten minutes at an exact overall average of 10 Mb/s occupies 750 MB. File size and duration develops this calculation for a complete file.
For playback, the average hides changes through the presentation. Pictures with more encoded data consume the buffer faster than simpler pictures. A rate measured over one second and a rate measured across the whole film summarize different intervals.
Bitrate is consequently a useful data budget, not a measurement of resolution or a quality score. To judge the encoding, compare the reconstructed pictures or sound. To judge delivery, compare data demand over time with arrival and available buffering.