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

Paul B Mahol onemda at gmail.com
Sat Jun 17 21:08:11 EEST 2023

On Sat, Jun 17, 2023 at 2:48 PM Michael Niedermayer <michael at niedermayer.cc>

> Hi
> On Sat, Jun 17, 2023 at 01:08:45PM +0200, Paul B Mahol wrote:
> [...]
> > But the biggest issue is your claim of demultiplexing, which your code
> does
> > not do, its done by called library.
> libsoapy is used just as a thin and common interface to the SDR hardware
> If you comment all uses of libsoapy out and use a file, it will still work.
> To be clear, you can dump a raw file with the "-dumpurl" option and
> lets say dump the radio spectrum from 6mhz to 16mhz (thats 40mbyte per
> second)
> and sdrfile with no libsoapy (if you comment that out) will play all AM
> radio
> stations from that range from just that file. That might be 10 or many more
> from the single input stream.
> Neither the SDR hardware nor libsoapy have split the radio stations in that
> 40mbyte/sec stream. Its basically just raw data from the hardware analog
> digital
> converter(s).
> The way SDR HW works is very simple. It has an antena an amplifer and at
> that
> point it might have 1khz to 6ghz of spectrum.
> that is then run through a mixer or 2 to shift the part of the spectrum one
> is interested in, into the lower frequencies (where its easier to work
> with)
> and that is then run through a low pass filter and 1 or 2 analog digital
> converters and their output goes over your favorte USB cable into sdrdemux
> that time domain signal that sdrdemux/sdrfile then gets is then analyzed in
> sdrdemux to find all radio stations and then depending on how its
> configured
> it will demodulate one or all.
> >
> > The correct place for this code is in libavfilter. Where user could
> select
> Besides that sematically its the wrong place (as i said in my previous
> reply)
> libavfilter is technically wrong too
> sdrdemux for DAB will return a AVStream with digital compressed AAC
> sdrdemux for DVB will return a AVStream with digital compressed H.264 or
> MPEG2 video
> AVFilter has no support for digital compressed output.
> In fact really what sdrdemux will output is quite similar to what a
> matroska demuxer
> would, its a bunch of compressed and uncompressed streams, video and audio.
> That does not fit in avfilter.
> And you dont want it hacked into libavfilter either.
> One would want to use the AAC and h.264 streams losslessly, maybe store
> them in
> a matroska file but avfilter can only handle decompressed audio and video.
> Thank you for your comments!

Even if all that true above, which isn't.

Your solution is using seek hack that should be removed.

Which library handles compressed stuff?

> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> Those who are best at talking, realize last or never when they are wrong.
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