I now wonder why the YouTube profiles are 8000 and 10000 kb/s for 720p and 1080p respectively.
Simply put and just for illustration - a video file comprises of video and audio streams. Each is encoded at a bitrate therefore final file size is a function of both these bitrates and time.
Again simply put, at a given bitrate the higher the "resolution" (of either video or audio) the lower the "quality" - if you define quality as "information/sec" - so to speak.
So @1280x720 each frame is 921,600 pixels, @1920x1080 = 2,073,600 pixels. Equating pixels and bitrate (purely for illustration, as it is DEFINITELY NOT a direct correlation but it serves to make the point) you get less "information"/sec the higher the resolution for a given bitrate.
Hence smaller resolutions can be encoded at lower bitrates for the same "quality", conversely higher resolutions need higher bitrates.
In practice this is way more complex, which is why there are so many different codecs, variables and choices. With the more modern codecs, many folk would hold that one of the biggest factors in file size is video content ie no movement or constant whole frame movement. No movement tends to require very little encoding/compression, lots of movement the opposite.
As with most things in life, I suspect PD offers a compromise in it's pre-sets.
Cheers
Adrian
This message was edited 2 times. Last update was at May 27. 2011 04:01
Life is really simple, but we insist on making it complicated. (see below)
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