|reply to EliteData |
Re: Optimum App for Laptop: Bit-Rates?
Looking at the capture I see a series of HTTP "Get" commands, which I believe is the ABR algorithm requesting progressive higher bit rates when I first tune the channel (in this example Yes-HD).
So the Get data looks something like:
.../ yeshd.isml/QualityLevels(857000)/Fragments(video= ...
I am guessing the "857000" is the initial video stream bit-rate of 857 kbps.
The series of Get requests have progressively increasing quality levels (OK, with a dip in the middle)
857,000 => 2,913,000 =>1,445,000=>2,913,000
There are also a series of Gets for the Audio stream, settling at 96 kbps.
So the combined audio/video rate looks to be about 3 Mbps (if I am interpreting the QualityLevels parameter correctly).
There may be a series of other video bit rates below 2,913,000 bps, but the ABR algorithm requests the ones it thinks are likely to be the best (hence the reason it jumped from 857 kbps to 2.9 Mbps, then back down to 1.4 Mbps, and finally back to 2.9 Mbps. Also if I look at the total bit rate of the capture (with no other significant network activity other than the Optimum App) I see a bit-rate around 3 Mbps.
From what I have read the ABR client requests a "Manifest" from the ABR server that includes a list of the bit-rates available, so the laptop application knows what bit-rates are available.
I believe I found the ABR manifest XML file that is sent from the network to the ABR client in the capture. The manifest indicates there are four ABR streams made available for laptop streaming. I have listed these below (these are the MP4 video streams, audio is a 96 kbps stream that would added to the numbers below)
There may be a different set of streams for the iPhone/iPads, as these applications are not MS Smooth Streaming (Silverlight) based but rather Apple HLS.
ABR Streams for Optimum App for the Laptop
Bit Rate: 0.857 Mbps [~ 1.0 Mbps with audio]
Frame Width: 480
Frame Height: 270
Bit Rate: 1.445 Mbps [~ 1.5 Mbps with audio]
Frame Width: 640
Frame Height: 360
Bit Rate: 2.0325 Mbps [~ 2.1 Mbps with audio]
Frame Width: 960
Frame Height: 540
Bit Rate: 2.913 Mbps [~ 3.0 Mbps with audio]
Frame Width: 1280
Frame Height: 720