I have some MP3 audio files and AVI video files on my PC.
Looking at the properties of one of the MP3 files:
Size: 3,697,105 bytes
MP3 Audio 128 Kbps
Duration: 3m 51s
which makes sense- 128Kbps is 16 kilobytes per second, so this 231 second file uses (231 * 16) = 3696 kilobytes, which matches the file size.
Now, looking at the properties of one of the video files:
Size: 736,661,760 bytes
Duration: 2h 6m 44s
Audio stream: MP3 Audio 128 Kbps
Video stream: 25 fps XVID encoded, 94 Kbps
My first thought was “Woah! The video stream uses LESS data than the audio stream?”. This seemed unlikely- video is surely much more data-intensive than audio.
Furthermore, the sums don’t add up. The audio and video added up is 222 Kbps, or 13.875 kilobytes per second. The duration of the file is 7604 seconds. So the total file size should be (7604 * 13.875) = 105.5 Mb* approx- about 1/7 of the actual size.
Then I thought “Maybe the video stream is given in kiloBYTEs per second, not kiloBITs”, but the result still doesn’t tally: combined audio and video would then be 110 kilobytes per second, for a total file size of (7604 * 110) = 836.4 Mb approx
- I know, I know- 1Mb <> 1,000,000 bytes. I said approximately