Hey - hoping someone can show me what I'm doing wrong here....
I am publishing a stream from a single encoder at two bandwidths (384, 1500 - chunks in sync), and making each available via three edge nodes from the primary publishing point. Any of those play fine, and if I put all three node IPs in a muliple-A-record round robin DNS entry the Roku will pick one via DNS.
So I'm configuring my roVideoScreen like this:
video = CreateObject("roVideoScreen")
video.setMessagePort( CreateObject("roMessagePort") )
videoclip = CreateObject("roAssociativeArray")
videoclip.StreamBitrates = [384,384,384,1500,1500,1500]
videoclip.StreamUrls = [args.LowA, args.LowB, args.LowC, args.HighA, args.HighB, args.HighC]
videoclip.StreamQualities = ["SD","SD","SD","HD","HD","HD"]
videoclip.StreamFormat = "hls"
videoclip.Title = args.title
videoclip.SwitchingStrategy="full-adaptation"
video.SetContent(videoclip)
video.show()
The URLs are the fully qualified URLs to the low and high bitrate streams on three different edge nodes in different cities.
1) When I start playing the stream, it seems to always pick HighC (high bandwidth, third option). When I turned off that server, I expected it to choose a different server, but instead it threw Event 11 (Message "Unspecified or invalid track path/url.invalid") showed "Checking Connection" on the TV, and returned to the springboard. If I try to restart the stream, it errors immediately because server "C" is down, and returns to the springboard. Doesn't attempt to try server A or B. I'm assuming there's something wrong with how I've configured this - can anyone shed any light?
1a) I've noticed that it always seems to pick the last URL on my list. Is that coincidence, random happening, or mis-coding? (If it's not random I would also need to implement a way to shuffle the order of the A/B/C URLs to ensure load balancing, so that I don't wind up with all my audience on the same server)
2) I also have a question about how video URL switching works; I've noticed that a client may have a slow route to an edge node in one city, but good speed from other edge nodes - all down to the routing and which internet path their ISP sends them to reach each edge node. So in some cases, switching to a lower bandwidth is a quick fix to keep video running, but switching back to a DIFFERENT high bandwidth server is possibly the best solution for the rest of the broadcast, rather than staying on low bandwidth for the duration.
eg:
Edge Node A: Standard bandwidth - too slow - Roku switches down
Edge Node X: Low bandwidth - plays great - Roku considers switching up
Edge Node B: Standard bandwidth - hey this works fine because it didn't choose "A" again
2a) Should the Roku do this automatically? (It doesn't seem to)
2b) Do we know that it won't choose City A when it changes back to high bandwidth again - or is there a chance it will - and fail again?
2c) Once it finds a URL that works nicely, will it stay with it - or randomly switch away to other URLs at the same bandwidth level when it requests subsequent chunks? It seems the way I have it so far, it isn't switching at all, even if the server goes offline (!) - so I'm not super concerned about this just yet 🙂
3) Or - Is there any way I can change the URL list / setting on the fly, WHILE it's playing? If so I could implement this logic while the Roku is playing - and make load balancing and internet route selections in BrightScript code myself based on bandwidth/buffer reports.
4) Is there any way to get in touch with Roku Engineering to get clarification on how the internals of the adaptive bitrate switching actually work - and how it makes its stream selections? - in particular - if there are multiple URLs at the same bitrate, what is the selection criteria?
To summarise the goals are:
- Pick another stream if the server is down
- Switch to low bandwidth if high isn't sustainable
- Try returning to a different server at the high bandwidth if one didn't work well previously
And what I have so far is:
- Roku tries to play the last URL in the list. if it's not available or becomes unavailable it quits unceremoniously.
Thanks for any tips!!
