AES67

[Floris Daelemans]

Hi all,

At the latest IBC in Amsterdam I learned that there is quite an ecosystem of products from a variety of vendors that can bring lineair audio into the computer via IP.

There are two main flavours out there, Dante and Ravenna. They both build upon AES67, though there are some significant differences in the implementation and modes of operation.

This divide exists to such an extent that they don't even interoperate. 

I would like to put some effort into the development of an AES67 input for the encoder. Bringing lineair multichannel audio into the computer via IP and enabling the encoder to use that audio for DAB sounds good, no?

There is a good link between VRT and the Ravenna side of things, we collaborated on an proof-of-concept all-IP live television studio, so there might an opportunity there.

The reason we chose Ravenna was mainly because it is an open standard, whereas Dante isn't.

We didn't reach out to anyone yet, i thought i'd launch the idea here first and see from there.

Any thoughts?

Floris

[Nick Piggott]

Strong support from me for the idea. The fewer physical interfaces the better.

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[Peter Symonds]

Hi Floris

I will be willing to help. I have been able to playback Ravenna streams in Linux with gstreamer or dumprtp. You may be able to pipe it into the encoder?

Pete

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[Peter Symonds]

As I can remember you can request for a free 2 device soundcard for windows on their website if you need some sources for testing.

Pete

[Mathias Coinchon]

Hello,

This is a good point and we investigated in the past but there are currently no real open source implementation of AES67 that we could integrate.

I made a ticket in wishlist for VLC (so then we could use directly our encoders that rely on libvlc) but it has been put in low priority: https://trac.videolan.org/vlc/ticket/14771

The difficulty is also the need for synchronisation using IEEE 1588 (as specified in AES67) so this is something that should be implemented at OS level also.

However, it seems that VLC can already play AES67 streams (according to someone who went to AES67 plugtest workshop) as it is multicast with PCM in RTP frames according to the existing RFC. There will just be more delay and maybe synchronisation issues but this can be already a first attempt to "play" a AES67 stream.

I could not test this as I have no AES67 source but if you have one to test this could be helpful.

I think we all agree this is the way to go and get rid of these annoying soundcards that have all sort of problems. I'm willing to help as I can.

Mathias

---

De : Floris Daelemans <floris.d...@gmail.com>
À : mmbtools <crc-mm...@googlegroups.com>
Envoyé le : Jeudi 24 septembre 2015 14h13
Objet : AES67

[Matthias P. Brändli]

A surprising coincidence: I have just received an email from someone who
tried this using LiveWire equipment. His report:

Use the Axia SDP File Generator to create a SDP file of the stream
ftp://ftp.zephyr.com/pub/Axia/Tools/sdpgen.htm

Put the SDP file onto the local web server (I asked him why)

And use it with the VLC input.

dabplus-enc -v http://127.0.0.1/stream.sdp -b 80 -l -o file.dabp



His previous trial was using rtpdump and a pipeline with sox (which we
want to avoid).

rtpdump -F payload 239.192.94.237/5004 | \
sox -t raw -b 24 -e signed-integer -c 2 -r 48000 -B - \
-t raw -r 48000 dither -c 2 -b 16 -L -t raw - | \
dabplus-enc -i /dev/stdin -b 80 -f raw -l -o TheDestinationAddress:Port


Maybe that might be of help to you guys, I'm no expert in this stuff. If
you manage to find a nice way that works, please send me a scenario I
can put into the README and into the guide !

mpb

On 24. 09. 15 14:57, 'Mathias Coinchon' via mmbtools wrote:
> Hello,
>
> This is a good point and we investigated in the past but there are
> currently no real open source implementation of AES67 that we could
> integrate.
> I made a ticket in wishlist for VLC (so then we could use directly our
> encoders that rely on libvlc) but it has been put in low priority:
> https://trac.videolan.org/vlc/ticket/14771
> The difficulty is also the need for synchronisation using IEEE 1588 (as
> specified in AES67) so this is something that should be implemented at
> OS level also.
>
> However, it seems that VLC can already play AES67 streams (according to
> someone who went to AES67 plugtest workshop) as it is multicast with PCM
> in RTP frames according to the existing RFC. There will just be more
> delay and maybe synchronisation issues but this can be already a first
> attempt to "play" a AES67 stream.
> I could not test this as I have no AES67 source but if you have one to
> test this could be helpful.
>
> I think we all agree this is the way to go and get rid of these annoying
> soundcards that have all sort of problems. I'm willing to help as I can.
>
> Mathias
>
>

> ------------------------------------------------------------------------
> *De :* Floris Daelemans <floris.d...@gmail.com>
> *À :* mmbtools <crc-mm...@googlegroups.com>
> *Envoyé le :* Jeudi 24 septembre 2015 14h13
> *Objet :* AES67

> <mailto:crc-mmbtools...@googlegroups.com>.

> For more options, visit https://groups.google.com/d/optout.
>
>

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[Peter Symonds]

That might be quite handy seems Ravenna is RTP based. You could possibly modify the sdp file for Ravenna.

Pete

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[Mathias Coinchon]

Great, That's it ! he just proved that it works.  AES67 is very similar to Livewire and Ravenna, it's just that AES67 doesn't specify a discovery mechanism and so these 2 systems have their own way of doing discovery.

The SDP is necessary to describe the payload and stream parameters (sampling, resolution, packet time,..) but it's not rocket science.

Example SDP from the AES67 spec for a 8 channels , 24bits, 48kHz, 1ms per packet:

v=0
o=- 1311738121 1311738121 IN IP4 192.168.1.1
c=IN IP4 239.0.0.1/32
s=Stage left I/O
t=0
m=audio 5004 RTP/AVP 96
i=Channels 1-8
a=rtpmap:96 L24/48000/8
a=sendonly
a=ptime:1
a=ts-refclk:ptp=IEEE1588-2008:39-A7-94-FF-FE-07-CB-D0:0
a=mediaclk:direct=963214424

a, m and rtpmap are the important field that describes the multicast address, port and content of the RTP packets

We need to add this to the wiki documentation.

Mathias

---

De : Matthias P. Brändli <matthias...@mpb.li>
À : crc-mm...@googlegroups.com
Envoyé le : Jeudi 24 septembre 2015 15h11
Objet : Re: AES67

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[Mathias Coinchon]

Great, That's it ! he just proved that it works.  AES67 is very similar to Livewire and Ravenna, it's just that AES67 doesn't specify a discovery mechanism and so these 2 systems have their own way of doing discovery.

The SDP is necessary to describe the payload and stream parameters (sampling, resolution, packet time,..) but it's not rocket science.

Example SDP from the AES67 spec for a 8 channels , 24bits, 48kHz, 1ms per packet:

v=0
o=- 1311738121 1311738121 IN IP4 192.168.1.1
c=IN IP4 239.0.0.1/32
s=Stage left I/O
t=0
m=audio 5004 RTP/AVP 96
i=Channels 1-8
a=rtpmap:96 L24/48000/8
a=sendonly
a=ptime:1
a=ts-refclk:ptp=IEEE1588-2008:39-A7-94-FF-FE-07-CB-D0:0
a=mediaclk:direct=963214424

c, m and rtpmap are the important field that describes the multicast address, port and content of the RTP packets

[Nick Piggott]

I'm about to give this a go with some sources on a Livewire platform, so I'll let you know how we get on. The trick is definitely to drop it to RTP, and there's a blogpost on Telios' website that explains how to craft the SDP file. (http://blogs.telosalliance.com/tech/playing-livewire-streams-using-windows-media-player)

Nick

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[Peter Symonds]

There is a way of setting xNodes into Ravenna mode if you have one handy. There are instructions somewhere on the Telos website.

Pete

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