Re: [FFmpeg-devel] [PATCH] libswresample: avoid s16p internal processing format

[Michael Niedermayer <michael@niedermayer.cc>]

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On Thu, Jan 12, 2023 at 03:20:06PM +0100, Paul B Mahol wrote:
> On 1/8/23, Michael Niedermayer <michael@niedermayer.cc> wrote:
> > On Fri, Jan 06, 2023 at 07:04:59PM +0100, Paul B Mahol wrote:
> >> On Fri, Jan 6, 2023 at 7:01 PM Paul B Mahol <onemda@gmail.com> wrote:
> >>
> >> >
> >> >
> >> > On Fri, Jan 6, 2023 at 6:25 PM Michael Niedermayer
> >> > <michael@niedermayer.cc>
> >> > wrote:
> >> >
> >> >> On Thu, Jan 05, 2023 at 11:08:25PM +0100, Paul B Mahol wrote:
> >> >> > On Thu, Jan 5, 2023 at 9:53 PM Michael Niedermayer <
> >> >> michael@niedermayer.cc>
> >> >> > wrote:
> >> >> >
> >> >> > > On Thu, Jan 05, 2023 at 01:44:10PM +0100, Paul B Mahol wrote:
> >> >> > > > Patch attached.
> >> >> > >
> >> >> > > >  swresample.c |    3 ++-
> >> >> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> >> >> > > > eee7a0685b44aa867562138a2e2437ecb8844612
> >> >> > > 0001-libswresample-swresample-avoid-s16p-internal-transfe.patch
> >> >> > > > From 9c4cd60e2dd41cf98d693c8251f4cfade0807073 Mon Sep 17
> >> >> > > > 00:00:00
> >> >> 2001
> >> >> > > > From: Paul B Mahol <onemda@gmail.com>
> >> >> > > > Date: Thu, 5 Jan 2023 13:40:12 +0100
> >> >> > > > Subject: [PATCH] libswresample/swresample: avoid s16p internal
> >> >> transfer
> >> >> > > format
> >> >> > > >
> >> >> > > > Instead use float one by default for sample rate conversions.
> >> >> > > > The s16p internal transfer format produces visible and hearable
> >> >> > > > quantization artifacts.
> >> >> > >
> >> >> > > When does this occur and why?
> >> >> > >
> >> >> >
> >> >> > It occurs always. Just compare output with 16bit and
> >> >> > int32/float/double.
> >> >> > Look at other people report on internet.
> >> >> > Look at src.infinitewave.ca
> >> >>
> >> >> src.infinitewave.ca uses 32bit none of what it shows should touch the
> >> >> codepath
> >> >> you change.
> >> >>
> >> >> if we look at src.infinitewave.ca for swr we see 2 types of artifacts
> >> >> 1. Aliassing which is at maybe -120db with the actual signal at 0db
> >> >>    i would like to see some evidence that a human can hear this
> >> >>
> >> >
> >> > For s16p<->s16p it is much lower, around -78dB thus this patch.
> >> >
> >> > Also for others and reports for swr its is lower than exact -120dB
> >> >
> >> >
> >> > 2. Reflection and attenuation at the transition frequency
> >> >> With linear filters there is a tradeof between attenuation of the
> >> >> passband, reflection of frequencies beyond, latency and so on
> >> >> You can have a perfect sharp cutoff with no attenuation and no
> >> >> refelection
> >> >> that requires a infinitly long filter. And while this looks best in
> >> >> this
> >> >> frequency plot, does it actually sound best ? If you can hear -120db
> >> >> signals you surely would then also hear the ringing long before a
> >> >> gunshot
> >> >> from such long filter.
> >> >>
> >> >
> >> One can always change linear FIR to be min phase FIR kernel.
> >
> > I certainly would welcome a wider range of filters in swr, if you want to
> > add
> > any low delay sinc approximation or in fact i would welcome any filter
> > you want to add.
> 
> There is that afdelaysrc filter patch on ML to add FIR coefficient
> generation for fractional delay audio filter that can be also used as
> a interpolation FIR filter. And to me it seems better at same number
> of taps than already used/available ones in soxr and swr.

Please add improvments into swr, if you have any!


> 
> Also I have done prototype of resampling filter using afir filter via
> custom filters in filtergraph and it operates at similar speeds like
> soxr (in these very non optimized approach) and providing better/wider
> frequency output at highest band.

Can it be added into swr ?

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.

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