6 Music Live Hour @ 320

[Vangelis forthnet]

On Fri Jan 8 13:13:08 GMT 2016, James Scholes wrote:

> Is there any particular reason you use dashhigh2
> as opposed to dashhigh1 or just dashhigh?
> I'm a little confused, I must admit, why there are
> two and what the difference is between them.
> Do they each download from a different CDN?

Hi James

Some additional remarks on my command:
1. For AOD, --type=radio is not necessary with GiP 2.95
when using the --pid approach, as per:
https://github.com/get-iplayer/get_iplayer/commit/86d09e937ce091bd8a9b213a007af2f3b3fbb9f2
2. --radiomode (I used it by force of habit),
as is the case with 2.94, could be simply typed as --modes.
(All AOD & VOD modes have been consolidated, see
https://github.com/get-iplayer/get_iplayer/commit/8309ade6b77666ad56beb1ea159eb19f9ae4c9a3 )

Now to your questions:

> why there are two

for pid=b06sskk8, vpid=b06ssk9x
The relevant mediaselector/5 URL for desktop PC is:
http://open.live.bbc.co.uk/mediaselector/5/select/version/2.0/mediaset/pc/vpid/b06ssk9x
This URL checks your geo-location and prints
accordingly the available streams; for the UK,
you'd get inside the XML file a "dash" block
looking like:

<media bitrate="320" encoding="aac" expires="2016-01-26T04:00:00Z" 
kind="audio" service="stream-uk-audio_streaming_concrete_combined" 
type="audio/mp4"><connection authExpires="2016-01-09T02:24:54+00:00" 
authExpiresOffset="41159" dpw="50" 
href="http://aod-dash-uk-live.edgesuite.net/usp/auth/vod/piff_abr_full_audio/c27ed5-b06ssk9x/vf_b06ssk9x_e249e0a4-a58e-44d3-bc97-a5af20a4ec6e.ism/pc_hd_abr_v1_uk_dash_master.mpd?__gda__=1452286735_0cafca140f1c152bc4b377cd25303168" 
priority="1" protocol="http" supplier="af_akamai_uk_dash" 
transferFormat="dash"/><connection authExpires="2016-01-08T19:53:15+00:00" 
authExpiresOffset="17660" 
href="http://aod-dash-uk-live.bbcfmt.vo.llnwd.net/usp/auth/vod/piff_abr_full_audio/c27ed5-b06ssk9x/vf_b06ssk9x_e249e0a4-a58e-44d3-bc97-a5af20a4ec6e.ism/pc_hd_abr_v1_uk_dash_master.mpd?s=1452243535&e=1452286735&h=7288c7fa1fa09ba7e5e13b6108c583b9" 
priority="2" protocol="http" supplier="af_limelight_uk_dash" 
transferFormat="dash"/></media>

As you can see, there are two distinct CDNs
serving the dash audio streams:
supplier="af_akamai_uk_dash",  priority="1" (Akamai)
supplier="af_limelight_uk_dash", priority="2" (Limelight)

> what the difference is between them.

None as far as the stream itself is concerned;
one is the "main" CDN, the other is the fallback one;
"Jim web" of our list with his contacts inside BBC iPlayer Radio
may shed additional light on how stream requests
are being managed between the two of them...

> Is there any particular reason you use dashhigh2
> as opposed to dashhigh1 or just dashhigh?

 Choosing "2" was again a force-of-habit thing...
 If you just use dashhigh, you let GiP itself
decide; it does this by checking the highest priority value,
2 >1 => so a safe bet would be:
dashhigh1 = Limelight
dashhigh2 = Akamai

By doing so, GiP picks the CDN which is already more
busy with requests from browsers and other MPEG-DASH
compatible devices, I have come to the conclusion (but this is
based solely on my location and connection) that using the
"alternate" CDN will produce higher download speeds...
CDN loads vary considerably within a day; your end speed
may also be determined by your physical proximity to the
CDN node...
 I have not yet become familiar with the MPEG-DASH code
inside GiP 2.95dev, but off the top of my head have good reason
to believe that the "--exclude-supplier" switch still applies.
 Do a test for yoursel; issue

--modes=dashhigh --exclude-supplier=akamai

to fetch from Limelight, and then issue

--modes=dashhigh --exclude-supplier=limelight

to fetch from Akamai - you then decide which suits
you best...

Kind Regards,
Vangelis.

(By all means, I'm not infallible - please chime in
if you know better...)