Re: [FFmpeg-devel] [PATCH 5/6] fftools: avradio support

[Michael Niedermayer <michael@niedermayer.cc>]

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Hi


On Mon, Jul 24, 2023 at 10:19:08AM +0200, Nicolas George wrote:
> Michael Niedermayer (12023-07-24):
> > There are other pathes forward but thats the current plan _IF_ this
> > isnt killed off by the community and _IF_ others join and enjoy
> > working on this. Also nothing is cast in stone, this plan is intended
> > to be adapted as needed on the way.
> 
> I would love to play with this, but apart from the lack of time, I
> suspect using these patches requires some hardware I do not have. Can
> you tell a little about it?

sure, you can test it without hw, for example this:
https://samples.ffmpeg.org/sdr/klassik.sdr.bz2
bunzip
and
./ffplay klassik.sdr -rtlsdr_fixes 1 -video_size 1024x400

should play the sample

with hw, the cheapest i know of are the RTL-SDR DONGLES, you can get these
with an atenna and free shipping for less than 45$.
official page is this: (there are links to places to buy and pictures of
genuine and clones)
https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/
(theres also a list of "RECOMMENDED ALTERNATIVE SDRS" at the bottom of that page)

I also have a sdrplay rsp1a but this requires closed source drivers and
for me required to mess with build options in libsoapy interface to it
(disabling isochronous mode which didnt work reliably with my notebook)

Once you have the hw and libsoapy, antenna (or random wire) you can try
it with some random established software like cubicSDR, SDR++, sdrangel
or anything tomas mentioned.
or just the libavradio repository (ATM i do recommand to also apply all
pending patches to it as these often include bugfixes)
then a simple
./ffplay -sdr_freq 89M -f sdr x -video_size 1024x300

should open a vissualization of the radio spectrum at 89Mhz with any detected
vissible radio stations with their metadata and frequencies displayed
left and right arrow keys should allow moving to the next and previous
stations.

-dumpurl somefile.sdr
allows dumping the vissible radio spectrum to a file (big) and replaying
it later (this is very usefull for testing and debuging)

another important option is -gain
because if gain is too low theres nothing and if its too high all kinds of
cliping overflow and artifacts will cause problems.
there are 2 automatic gain control modes (one from hw and one in sw) and
you can just set the gain by hand.

ATM our code is able to detect some kinds of artifacts and seperate them
from real radio stations by the way they move in relation to the choosen
frequency.
Also the antenna should ideally be far away from any interference causing
electronics.



> 
> Also, is it only for receiving? It is there, at least as a potential,
> the possibility of sending, maybe in the Citizen Band?

ATM its receiving only. hw like the rtl-sdr or sdrplay rsp1a only support
receiving. There are SDRs that support transmitting though

transmitting support would be cool but thats for others to add.
Preferably someone who lives in a country with liberal laws about it and
who has already experience and all needed technical and legal things in place.

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
it to them? Then do not be too eager to deal out death in judgement. For
even the very wise cannot see all ends. -- Gandalf

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