[FFmpeg-devel] Exposing preroll and remainder info for aac and mp3.
michaelni at gmx.at
Tue Jul 10 15:06:39 CEST 2012
On Thu, Jul 05, 2012 at 02:21:36AM +0100, Kieran Kunhya wrote:
> On Wed, Jul 4, 2012 at 10:21 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Wed, Jul 04, 2012 at 04:24:51PM +0200, Michael Niedermayer wrote:
> >> On Wed, Jul 04, 2012 at 04:05:17PM +0200, Nicolas George wrote:
> >> > Le septidi 17 messidor, an CCXX, Michael Niedermayer a écrit :
> >> > > are there some reference files (mp3/aac + wav refernce of what should
> >> > > be the delay free output ?)
> >> > > These would be very usefull to implement this as well as for
> >> > > regression tests so it doesnt break in the future once it works.
> >> >
> >> > Is it really necessary? We can see for ourselves with any audio file that
> >> > does not have too much silence on the beginning. For example:
> >> >
> >> > ffmpeg -f lavfi -i aevalsrc='abs(sin(2*PI*t))*sin(2*PI*440*t)::d=10' \
> >> > test.mp3 test.wav
> >> > ffmpeg -i test.wav -i test.mp3 -filter_complex '
> >> > [0:0] showwaves=n=15:s=1470x64, pad=iw:ih*2 [a] ;
> >> > [1:0] showwaves=n=15:s=1470x64 [b] ;
> >> > [a] [b] overlay=0:64' -vframes 1 test.png
> >> >
> >> > The output.png shows clearly a 74 pixels delay for the MP3 file, which makes
> >> > about 1110 samples.
> >> >
> >> > I believe our purpose should be that a round trip encode+decode gives a file
> >> > that is in sync with the original. lame + lame --decode does that, for
> >> > example.
> >> we should aim toward getting our decoder round trip exact with any
> >> other encoder be that lame, faac, ffmpeg, itunes or other.
> >> for this we need sample files from all these encoders.
> > just posted a patchset implementing initial silence skiping for mp3
> > doing the same with mov/mp4 aac should be trivial, id need a reference
> > sample though to make sure the aac/mov/mp4 stuff is correct. Its easy
> > to get it wrong without a testcase ...
> > the mp3 code should be compatible with lames way of indicating the
> > amount of padding.
> > [...]
> > --
> > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> > The real ebay dictionary, page 1
> > "Used only once" - "Some unspecified defect prevented a second use"
> > "In good condition" - "Can be repaird by experienced expert"
> > "As is" - "You wouldnt want it even if you were payed for it, if you knew ..."
> The Fraunhofer Android encoder/decoder refers to this paper so it
> might be of use:
> Lutzky, Schuller, Gayer, Krämer, Wabnik, "A guideline to audio
> codec delay", 116th AES Convention, May 8, 2004
do you have a link to that paper ?
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
During times of universal deceit, telling the truth becomes a
revolutionary act. -- George Orwell
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