A first look at Larix Broadcaster

Noticed that the Larix Broadcaster iphone app supports both RIST and SRT, so had a quick look.

We have an MWEdge device (called “wedgie”) which listens for SRT and RIST via the internet and outputs them as multicast RTP for our decoders to decode to SDI. We’ve used this successfully for a backup h265 stream from the recent Biden Inaugeration, where we took a h265 stream from another broadcaster, which worked well.

The App

Setting up Larix is easy enough, although it’s not immediately obvious when you’re streaming or not streaming from the button – look at the clock in the top corner to confirm it’s streaming

Likewise the mute button goes white when muted, and transparent when not muted, but there’s no change to the colour of the volume bar on the left

Larix outputs 1920×1080 (many different options upto 3840×2160) in 16:9 landscape format (portrait is available on some streams), even when the phone is in Portrait-Lock mode, which is good, and an improvement on other iphone stream apps I’ve seen.

You can choose a framerate (15/25/30/50/60), and as a European I want 25fps. It has a keyframe frequency so I’m assuming it’s IPPP frames?

When I connect in on SRT, MWEdge shows the connection, although my test isn’t currently too challenging from a material or network perspective

Saturating my upstream bandwidth with a quick iperf (for a second) shows SRT coping. Clearly if you want latency less than 1 second, no error correction will cope with an outage of 1 second though.

But the question is, does it stream?

I haven’t yet figured out how to extend my multicast domain over my wireguard connection, so it’s a matter of using multicat to copy the data to a local vlc instance listening on rtp://@:6000

Latency isn’t great with default VLC settings, and I haven’t tried any SRT tweaking either, but a quick test of loading shows about 3.2 seconds, clearly no good for live broadcast, but as I say VLC buffers aren’t great for this type of test.

How does the stream look?

OK, not good. It’s supposed to be 25fps, that could just be VLC though. FFMPEG looks better

So, will it decode on a proper broadcast device? They are notoriously picky. Lets fire to my test OBD and AppearTV X10 channels


OK that seems to work at first blush. The server name and provider isn’t present and OBD doesn’t blank the previous one.

But the detected output is a bit odd

If I force it to 1080i25, or even 1080p25, the OBD is not happy. Remote monitoring does not show anything useful coming out of the box, but that’s set up for 1080i25 only. This will have to wait until I can get back into the office.


Like the OBD this shows an incoming stream

Traffic seems to be coming in, but the video contents is decodes as 0x0p50 and doesn’t actually output anything

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