[PLUG-AV] Another experiment in updating our AV workflow

[James Henstridge]

On Tue, 18 May 2021 at 09:31, Harry McNally
<harrymc at decisions-and-designs.com.au> wrote:
>
> Hi James
>
> On 17/5/21 4:00 pm, James Henstridge wrote:
> > I haven't done much work on that code base since March.  The last
> > thing I was working on was to try and simplify the configuration
> > process so you wouldn't have to write GStreamer pipelines in the
> > general case: instead, you could tell it that you want to use a
> > particular camera at a particular resolution and framerate, and have
> > it figure the rest out.  With that said, I believe the code should
> > still function as is.
>
> If you have time to describe the Raspbian setup for testing the work to date
> on the list, would it assist if I prepare an SD card for the RPi4 I have to
> bring along to the next meetup ?

The test setup I created at the Raspberry Pi Jam was using an Ubuntu
Server 22.04 image as a starting point, and building the software on
the board itself.  You can probably build on Raspbian, but I haven't
checked. I don't have a full list of dependencies, but you'll probably
need at least the following:

1. git (to clone the repository)
2. meson (the build system)
3. libgstreamer1.0-dev
4. libgstrtspserver-1.0-dev
5. libavahi-client-dev
6. libavahi-glib-dev

To build the project, you'll probably want to run the following
commands from a checkout:

    mkdir build
    cd build
    meson -Dobs-plugin=false ..
    ninja

The repo contains both the RTSP sender and the matching OBS plugin.  I
suggest disabling the OBS plugin as it is only needed on the system
that will receive the streams, and I had trouble building it on armhf.


> It will give me time to prepare so I can drop in and do integration testing
> quickly. If you do any additional work that requires change on the RPi4 let me
> know again and I can tweak.
>
> Also, if Nick's capture device suits, may I suggest deleting the USB hub and
> use a USB extender cable:
>
> https://www.ple.com.au/Products/624625/Startech-1m-Black-USB-30-Male-to-Female-USB-30-Extension-Cable-A-to-A
>
> I didn't see a 15cm one and I have purchased very short HDMI cables before so
> it is worth considering if the RPi4 should be up next to the camera or on the
> floor with a longer HDMI cable and purchase test cables to suit.

I think it would probably be better to prefer a longer HDMI cable over
a longer USB cable in connecting up the capture board: it'd be good to
minimise the amount of unsupported weight hanging off the camera's
HDMI socket.

The USB 3 ports on the RPi4 are right against the Ethernet socket, so
we probably would want some kind of extension cable if we are using
dongle-style capture boards like the one Nick bought. We can probably
do shorter than 1 metre though, such as this one:

https://www.amazon.com.au/dp/B01M1KINRO

Of course, Nick's dongle only supports USB 2.0 speeds. I wonder if
there are any performance benefits on the RPi side from having it
plugged in to one of the 3.0 ports?

>
> > I haven't really investigated sending audio yet.  You can definitely
> > transmit audio with RTSP/RTP, so it would probably just work with an
> > appropriate pipeline.  I hadn't really investigated much further
> > though, since our use of wireless microphones reduces the need for
> > remote audio: we could just plug the audio mixer directly into the
> > machine running OBS Studio.
>
> This makes sense. When I get a moment, I will post a mixer requirements to the
> list for scrutiny. Once I know what features are needed I can review those USB
> powered mixers.

James.