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

[Lynne]

Jun 17, 2023, 20:37 by michael at niedermayer.cc:

> On Sat, Jun 17, 2023 at 08:08:11PM +0200, Paul B Mahol wrote:
> [...]
>
>> Which library handles compressed stuff?
>>
>
> For digital stuff like DAB/DVB/...
>
> sdrdemux in libavformat will demodulate, do error correction then return  AVPacket
> with H.264 / Mpeg2 video or AAC or wahetever
> That then will get passed to libavcodec, same as with any other demuxer.
>
> This code is not written yet. There is just analog AM demodulation. I posted
> this patch as soon as the first usecase worked
>
> usecase was "listen to random AM radio stations in ffplay" :)
> and it can also grab all AM stations in a 10Mhz window and demodulate all
> (that 10mhz is what my hw and usb bandwidth can do max)
>
> I intend to add FM demodulation, because it seems a fun thing to try to do.
>
> someone will need to add DAB/DVB support, I would be happy if someone else
> comes forth to do that. If noone does ill think about if i want to do it
> or not once FM is done and once this is in git.
>
> The initial reaction from some was a bit spicy, so i need to think
> how much fun this is in FFmpeg.
> But one thing i can say for sure, is, if i cannot use this in ffplay
> then it makes no sense for me to put more time into it
>
> We could implement seeking to next/previous stations differently but
> it seems a bit like creating extra work for everyone.
> I mean a new API in sdrdemux then ffplay needs to support that and then
> other players would need to support it and so on. While really the
> seeking on a realtime input has no other use
>

I like the new functionality, but I too think that libavformat
should just source the data from a device, and that libavfilter
should demodulate. There are applications for which you'd
like to store the raw Mhz/Ghz audio data as well as the
decoded data.

Additionally, filters can receive commands, while demuxers can't,
so switching stations would be simpler.