Building a Multicast TV Distribution System on Your Home Network
Multicast TV Distribution on My Home Network
I explore the unique mechanics of multicast to distribute live TV across my home network, inspired by Tall Paul Tech. By using ffmpeg to stream media without heavy transcoding and configuring FRR for routed multicast, I demonstrate how this approach can significantly upgrade network capabilities for niche use cases while saving CPU power.
Today I am taking a look at the weird world of multicast, where packets get delivered more than once, and we route using a backwards routing table.
- throw0101d
The N Is For Networking podcast (from Packet Pushers) has a recent two-parter on multicast:
- urams
Interestingly multicast is used extensively by exchanges to distribute trading data to participants. I think it's the primary commercial usage outside of some IoT things.
- cletus
I worked on Google Fiber's TV distribution system so know something about this although GFiber's TV offering was IPv4 multicast not IPv6.
For anyone unfamiliar, modern video codecs tend to break up a video into a group of pictures (GOP) and you have a mix of different frame types. Some of these are the entire image. Most are just differences. It gets more complex as the video codecs allow you to pull objects from previous and future frames. But I digress.
The point is one of the things you have to decide is how often you send a complete image. Typically that's every 1-2 seconds. It may be more often with scene changes. The bigger the minimum gap in full images, the lower the bandwidth. The downside? The longer it takes to start playing a channel. Also, it makes network interruptions worse as you may have distorted the image and sound for up to 2 seconds instead of 1.
You also have to make a choice between CBR (constant bit rate) and VBR (variable bit rate). CBR is often preferred for mass distribution because it doesn't overload what are usually lower powered CPUs but that will also lead to a delay in channel changes as a full image may take longer than 1/24 or 1/30 of a second to actually send.
And then when you get into sending video over a network you have to worry about some Russian dolls of various standards. The video has a format. So does the audio. Those are in a container format (eg MKV). And then you have a transport format. For Fiber this was (and probably still is […]