[MEncoder-users] Flashvideo for YouTube using mencoder
jultus at gmail.com
Fri Feb 22 18:06:48 CET 2008
On Fri, Feb 22, 2008 at 4:01 PM, Rich Felker <dalias at aerifal.cx> wrote:
> It also just looks unprofessional and low quality when you get a file
> and the header says some random fraction approximating 29.970 instead
> of the exact value 30000/1001 (or likewise 23.976 instead of
> 24000/1001). It's not so much that it will cause a practical problem
> for the vast majority of users, but that the wrong framerate sets off
> a warning flag of "oh the person encoding this probably didn't know
> what they were doing so maybe they made other mistakes like bad
> inverse telecine, harmful encoder options that hurt quality, bad
> filters, etc."
Let's not forget, the target here is YouTube, so, not intended
for much post-inspection or further processing. (There are those
who actually pull the flv from their browser cache and use it again,
but these people don't care much about quality..)
You forgot to mention why the 29.97 frame rate exists. I actually
know this quite well, since I work in broadcasting;
When television was first beginning, there weren't any of the microchips
that we use in this task today. Because of that the engineers back then
used the oscillation of alternating current from the electricity outlet
as the basis for their timing circuits.
In the US electricity cycles at 60 times per second (60 Hertz). Half of that
gives us the frame rate of 30fps. The framerate of television was actually
exactly 30 frames per second at one point in time.
That changed when colour television was introduced. When a signal for
colour information was added to the television transmission a problem arised;
The colour carrier signal was interfering with with the sound carrier signal
because they were very close in the spectrum. This made video un-
watchable. The quick fix they came up with was to reduce the framerate
by .03fps which moved the two signals enough out of phase to stop
interference. The world has been stuck with this frame rate ever since..
There's a fascinating history on frame rates here:
For Flash Video one can use 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 frames/sec.
and it all works fine, as long as it encompasses the movement in the video.
I found out that in practice 21 fps for video-logging, where the only
mouth, face, hand based, is perfectly fine, for example. Which saves a
lot of data.
Anyway, hope this info is helpful for some..
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