320kbps radio audio available via MPEG-DASH

[James Scholes]

Jim web wrote:
> I think I now need to sort out switching to HLS for radio fetching rather
> than RTMP! :-)
> 
> I've been talking to someone, and my initial AIUI is...
> 
> The 320k via HLS has been available for some months for most of the BBC
> stations. The focus has since been on having this also via MPEG-DASH, plus
> allowing the bitrate to be adaptable under the control of the
> player/client.

Always great to hear your insights, Jim, but this doesn't seem correct.
 Let's take a look at yesterday's Afternoon Drama on Radio 4 as a test
subject.

If you happen to have an API key for Nitro, you can check which
mediasets are available for the program:

http://nitro.api.bbci.co.uk/nitro/api/programmes?api_key=<your_api_key>&mixin=versions_availability&pid=b06tvhnj

No worries if you don't, but from the obtained list of mediasets, we can
see that there are a number that support HLS streaming.  Let's try the
most common one:

http://open.live.bbc.co.uk/mediaselector/5/select/version/2.0/vpid/b06tvhn1/format/xml/mediaset/apple-ipad-hls

Which yields one selection at 128k:

<media bitrate="128" encoding="aac" expires="2016-02-06T15:00:00Z"
kind="audio" media_file_size="46827540"
service="stream-uk-audio_streaming_aac_med" type="audio/mp4">

This remains the case despite which mediaset we ask for (iptv-all,
journalism-http-tablet, apple-iphone4-hls, etc).  They all return data
for an HLS stream at 128k.

On the other hand, if we query the mediaselectorr for the audio
available via DASH:

http://open.live.bbc.co.uk/mediaselector/5/select/version/2.0/vpid/b06tvhn1/format/xml/mediaset/pc/transferformat/dash

<media bitrate="320" encoding="aac" expires="2016-02-06T15:00:00Z"
kind="audio" service="stream-uk-audio_streaming_concrete_combined"
type="audio/mp4">

We see that the audio is available at 320k.  Finally, let's check what
you would get if you used an iOS device to download the program (with DRM):

http://open.live.bbc.co.uk/mediaselector/5/select/version/2.0/vpid/b06tvhn1/format/xml/mediaset/apple-ios-download-high

<media bitrate="320" encoding="aac" expires="2016-02-06T15:00:00Z"
kind="audio" media_file_size="1811"
service="download-uk-audio_download_drm_aac_high" type="audio/mp4">

Of course, this is just one program of many, but I did try exactly the
same procedure with a program from Radio 3, which are traditionally
offered in higher bitrates, and saw the same results.  But to sum up:

- If you stream radio via HLS, you'll probably get 128k AAC.
- If you stream the same program via DASH, you'll probably get 320k AAC.
- If you download the DRM-protected version of the same program on your
mobile device, you get 320k AAC.

Of course, if the BBC say that HLS should offer 320k, then there's no
reason to doubt their word.  But in this instance, their own APIs report
that it isn't available, so DASH is the clear winner.
-- 
James Scholes
http://twitter.com/JamesScholes