[FFmpeg-devel] [PATCH 5/5] avformat: add sdr support

Paul B Mahol onemda at gmail.com
Sat Jun 17 14:08:45 EEST 2023

On Sat, Jun 17, 2023 at 10:46 AM Michael Niedermayer <michael at niedermayer.cc>

> On Sat, Jun 17, 2023 at 08:16:04AM +0200, Paul B Mahol wrote:
> > Please no more pseudo demuxers.
> >
> > Use libavfilter API.
> sdrdemux takes a single linear stream of numbers containing multiple radio
> stations and demuxes it into individual streams
> (the stream can come from a file or a hardware device)
So it takes vectors of numbers. And not really big vectors of bytes?

This have nothing to do with demuxing. Demuxing needs input bytes and then
by some logic it splits and separates it into something else,
but this code does not handle raw bytes, that handles another library.

But nice try to bring again lies here.

> This is litterally the definition of demuxing
> just the first line from wikipedia about it "Demuxer" (which redirected
> to) "Multiplexing"
> "In telecommunications and computer networking, multiplexing (sometimes
> contracted to muxing) is a method by which multiple analog or digital
> signals are combined into one signal over a shared medium. The aim is to
> share a scarce resource - a physical transmission medium."
> "A device that performs the multiplexing is called a multiplexer (MUX),
> and a device that performs the reverse process is called a demultiplexer
> (DEMUX or DMX)."
This is exactly what radio transmissions are, multiple radio, tv,
> telecommunication, digital, analog signals are transmitted over the shared
> radio wave channel.

Your code "demuxes" user supplied numbers that represent frequency of radio
and also creates own pseudo version of container to hold whatever it

> If you look at https://en.wikipedia.org/wiki/Multiplexing
> The 1st diagram to the right on th e1st page lists litterally AM, FM on
> the 2nd line
> under Multiplexing
> if sdrdemux should be a avfilter, than every demuxer we have should be a
> avfilter too.
> Iam not objecting to that, but thats not how avfilter and avformat is
> structured today. Demuxers in FFmpeg are not AVFilters

Your logic and reasoning, is again, completely, flawed.

If you know basic physics, how electro-magnetic waves propagate in space,
you would notice that radio takes only little subset of infinity. So its
already demuxed at that part.
But the biggest issue is your claim of demultiplexing, which your code does
not do, its done by called library.

The correct place for this code is in libavfilter. Where user could select
frequency at will, and not use pseudo seek functionality that does not seek
at all in timeline.
Unless you found way to really seek within AM radio content in time, in
which case I applause your invention, I'm sure that such invention would
fix all our stupid issues as humans and more. So again, huge respect to you
Sir, good job, and continue doing that job, and do not mind my rambling!

> Thx
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> I am the wisest man alive, for I know one thing, and that is that I know
> nothing. -- Socrates
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