On 02/08/2012 09:08 AM, Alexandre Prokoudine wrote: > On Wed, Feb 8, 2012 at 11:32 AM, Simon A. Eugster wrote: > >>> http://jeff.ecchi.ca/blog/2011/07/25/automated-multicamera-clip-syncing/ >> >> I have no idea how you manage to have a link to a solution for nearly >> every problem. Thanks for the link! > > YW :) > >> How accurate can we position audio streams? Just by full frames, or is >> it possible to have a finer granularity? When I synced audio/video I >> often had the problem that the audio was too early and after moving it >> by one frame it was too late. > > Admittedly, I haven't had a chance to test it myself yet. However > http://bemasc.net/wordpress/2011/07/26/an-auto-aligner-for-pitivi/ > states:
Already read! :) I rather meant kdenlive/MLT here. Can we move an audio clip by just a few samples or only by full frames? Simon > "The algorithm I settled on resembles the method a human uses when > looking at the waveform view. First, it breaks each input audio stream > into 40 ms blocks and computes the mean absolute value of each block. > The resulting 25 Hz signal is the ?volume envelope?. The code > subtracts the mean volume from each track?s envelope, then performs a > cross-correlation between tracks and looks for the peak, which > identifies the relative shift. To avoid performing N^2 > cross-correlations, one clip is selected as the fixed reference, and > all others are compared to it. The peak position is quantized to the > block duration (creating an error of +/- 20ms), so to improve accuracy > a parabolic fit is used to interpolate the true maximum. I don?t know > the exact residual error, but I expect it?s typically less than 5 ms, > which should be plenty good enough, seeing as sound travels about 1 > foot per ms." > > Alexandre Prokoudine > http://libregraphicsworld.org > > ------------------------------------------------------------------------------ > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnow-d2d > _______________________________________________ > Kdenlive-devel mailing list > Kdenlive-devel at lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/kdenlive-devel
