Re: [ecasound] ecasound time accuracy

From: Kai Vehmanen <kvehmanen@email-addr-hidden>
Date: Wed Aug 31 2005 - 23:42:31 EEST


On Wed, 31 Aug 2005, sebastien Pastor wrote:

> I am very new to ecasound and my use is a very basic one. I am trying to use
> it to cut and join waves files. i need to have a "frame" accuracy to stick
> to the video the wav is extracted from. strangely when i use such a command :

Ecasound is not necessary the best tool for the job as it always handles
audio in blocks. For sample-accurate operations (like looping), Ecasound
does offer the .ewf format, but this cannot, in its current form, be used
for cut&paste use.

> ecasound -i test.wav -o out.wav -t:104.36

As a hack-solution, you can force ecasound to use one-sample blocks by
adding -b:1 to the command-line.

> out.wav appears to be 104.344 (from a get-length) (so after a while on long
> videos the audio is drifting ...)

This is a result of rounding 104.36 to the current blocksize. The default
is -b:1024, which with 44.1kHz sampling freq results in
1024/44100*1000=23.22msec resolution. With -b:1, you already get 0.02msec

> Could anyone tell me how i could achieve a "frame" accuracy ?

With video frame rate of 30 (~33msec between video frames), -b:16
(<1msec) or lower should be accurate enough.

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Received on Thu Sep 1 00:15:08 2005

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