[Lumiera] Audio editing

C Wilson have.footage.will.edit at gmail.com
Tue Jul 7 02:33:10 CEST 2009


*NTSC is not 23.97 it is 29.97* ( hence the need for the 3:2 pull down to
convert feature films shot in 24fps to play correctly at 29.97. PAL and
SECAM these two standards work at 25fps.(SECAM is not used for editing due
to artifacting and personally its a pain in the under side to edit - most
(if not all ) SECAM is converted to PAL then back for broadcast. As it
stands only Russia, some parts of Africa and possibly Iraq and Iran use
SECAM)  48khz audio for cameras come in two flavors. locked and unlocked, DV
(consumer) is usually unlocked however I have used some DV cameras that have
locked audio. DVCPro, DVCAM and I do believe HDVpro uses locked audio. any
multiple of 48 should be able to sync almost perfectly as long as the audio
is LOCKED to the video.

In AVID if you were to import audio from a CD or any source that had 44.1
audio it would upsample the audio ( pitch intact) to allow better synch.
There are white papers on to why 48khz audio works better for video than
44.1. I just got to find them. One thing though .. back in the early days of
PCM there were devices that you could hook up to your VCR that would allow
you to record digital audio - worked great.. the only "gottcha" was that it
had to sample at 44.056 due to the nature of analog NTSC timing. eventually
they did have a way to do 44.1 but its really bad news for any form of
editing... 48 just slices well with 30fps, 24fps and the such since you can
get an even number of audio frames to every video frame... hope this
helps... I will look for the white pages for I think that it will help ..
*NTSC = 29.97* (30fps aka 1000/1001) the .03 differential is due to when
NTSC went to color the color burst part of the signal delayed the luminance
part by .03 of a frame ... hence 30drop
*PAL/SECAM* = 25fps (24.97) - I am not sure if that standard requires drop
frame but if it does then 24.97 is assumed.

*FILM/CINEMA* = 24fps the 23.97 is after a pulldown then ramped up for
NTSC/ATSC standards.


here is a link regarding the video standards ..
http://en.wikipedia.org/wiki/Video

PEACE
CJ


On Sun, Jul 5, 2009 at 1:30 PM, Ichthyostega <prg at ichthyostega.de> wrote:

> hendrik at topoi.pooq.com schrieb:
> > On Sun, Jul 05, 2009 at 05:15:38PM +0200, Christian Thaeter wrote:
> >> Ichthyostega wrote:
> >>> ... For everything I am aware off, the frame rate was fixed to a
> limited
> >>> set of values dictated by hardware, eg. 8000, 44100, 48000, 96000,
> >>> 192000, etc.
>
> >>> Christian Thaeter schrieb:
> >> That are sample rates, dunno if one wants to call single audio samples a
> >> frame :)...
>
> yes, "audio sample frame" is a common term. Which seemed to have confused
> me ;-)  because Juan probably referred to the NTSC video framerate (23.976)
> -- thanks for pointing that out!
>
> I think, for the most common video framerates, we should provide fixed
> identifiers on the API/GUI (and internally represent them as rational
> numbers).
>
> >> .... Even worse, a lot of (consumer) cameras clock drift depending on
> >> temperature, moon-phase and mood, the audio sample rate is not exactly
> >> 48kHz but some Hz more or less (i'd guess frame rates may drift too).
> Some
> >> people told me that this gives noticeable audio desyncs depending if the
> >> camera was warm or cold. We'll face endless fun with such things :).
> Yes, can confirm that. Both image and sound framerate can drift on consumer
> cameras, which gives you endless headaches esp. when filming a musical
> event
> with several such cameras....
>
> >> I think some automation for frame/sample rate fine adjustment controling
> >> some noise gate (extend/compact silent phases) or frame drop (or
> doubling)
> >> might be a forseeable tool to correct that.
>
> we could try to find a solution here; but I'm rather sceptical with regards
> to
> getting sound automatically synched to the image. Maybe a semi-automatic
> tool
> could work. But even a tool of the sort "pin this (mouse click in waveform)
> sound elm. to that video frame and stretch sound if necessary" would be a
> great
> help for this tedious task...
>
>        Hermann
>
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