Re: [FFmpeg-devel] [PATCH] libavcodec/flacenc: Enable sample rates > 655350 Hz

[Michael Niedermayer <michael@niedermayer.cc>]

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On Tue, Nov 15, 2022 at 05:14:26PM +0100, Martijn van Beurden wrote:
> Op ma 31 okt. 2022 om 19:33 schreef Martijn van Beurden <mvanb1@gmail.com>:
> >
> > Op ma 31 okt. 2022 om 17:58 schreef Derek Buitenhuis
> > <derek.buitenhuis@gmail.com>:
> > >
> > > It is interesting that the IETF RFC and the Xiph spec disagree on whether this is allowed.
> > >
> >
> > The Xiph spec also says the IETF spec is better, and it remains as
> > historical reference and overview :)
> >
> > > The Xiph spec says:
> > >
> > >     Sample rate in Hz. Though 20 bits are available, the maximum sample rate is limited by the
> > >     structure of frame headers to 655350Hz. Also, a value of 0 is invalid.
> > >
> > > The RFC just says:
> > >
> > >    Sample rate in Hz.
> > >
> >
> > The spec as it is on the FLAC website (which is being "preserved") is
> > wrong. I don't know how this came to be, I think it was at first
> > poorly worded and later incorrectly fixed. See this commit:
> > https://github.com/xiph/flac/commit/96534bb5f35eb9c2f6f393dc470625e9c74df1a5
> > The text as it was before that commit doesn't make any sense, the text
> > as it is after the commit is not correct either.
> >
> > The issue here is that FLAC has a sample rate in the streaminfo
> > metadata block, at the very start of the file. That one can
> > accommodate sample rates up to 2^20-1. The frame headers repeat the
> > sample rate every frame and can only accommodate up to 655350Hz, but
> > they can also reference the streaminfo metadata block. Because of the
> > possibility to reference that 20 bit number, it is possible to store
> > sample rates up to 1048575Hz. You can see this patch only touches the
> > encoder: the FFmpeg decoder has already been equipped to deal with
> > this since its inception in 2004.
> >
> > There is some kind of limitation to sample rates above 655350Hz, or
> > samplerates between 65535Hz and 655350Hz that are not a multiple of 10
> > though: a FLAC file with such a sample rate cannot be multicast,
> > because a decoder receiving a multicast stream does not receive the
> > streaminfo metadata block, and thus cannot use it to figure out the
> > correct sample rate.
> >
> > Please let me know when this explanation falls short.
> >
> > Kind regards, Martijn van Beurden
> 
> Hi all,
> 
> With this email, I would like to renew the attention of the mailing
> list for this patch.

will apply

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA

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