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Audio Factory: an overview

Andrew Scott

General Manager


as General Manager of Radio Product for BBC Future Media I am responsible for all the BBC’s online radio services.

This week marks one of the final milestones of the Audio Factory project, which many of you have contacted us about, so I wanted to clarify what is changing, provide some context and an update on the changes that have already happened.

What is changing?

By the end of this week we will have turned off all the Windows Media Audio on demand services.

What does that mean?

This means that users with devices that today use those WMA on demand streams, typically Internet Radio devices, will either

- Be migrated by their manufacturer to our new streams and continue to have access to on demand content, or

- Be waiting to be migrated by their manufacturer to our new streams so that they will then be able to have access to on demand content, or

- Will not migrate, in which case they will continue to have access to Podcasts, but will not have access to other shows on demand.

Collectively these WMA on demand streams currently represent around 2% of listening on our most popular programmes.

Why is the BBC doing this?

We are replacing our entire audio delivery system and following careful evaluation decided not to include support for Windows Media Audio (WMA). WMA is an old proprietary format that is no longer supported by our technology partners.

What is Audio Factory anyway and why did you have to change anything?

"If it isn't broken, don't fix it" is generally true, but in this case the previous encoding technology system was broken.

It had been built up over a period of time by adding services as new proprietary technologies emerged, achieved critical mass and needed to be supported for our audiences. This process resulted in a great service for our audiences that kept up with changes, but under the bonnet some of the services were very fragile. We had dozens of issues over the last year where service was interrupted for some of our users. We also regularly had 32 times as many errors as successful streams for some of the stream types. This was not a system we could have just kept running. We also had a major contract coming to an end that meant that we had to replace the system.

We knew we had to change. We had also learnt from the success of Video Factory, a project which replaced all of our video encoding infrastructure, starting with the 2012 Olympics and now supporting all of iPlayer. So we started Audio Factory about 18 months ago by coming up with some principles that would help us through the project.

These included:

We want to build the most robust and reliable radio platform in the world with the highest audio quality availableWe want a consistent approach across all our radio stations, National, Nations, English Local, World Service and all the variations of those, because consistency and simplicity will drive reliability and cost effectiveness.

We will start with 57 stations but will be adding support for short term stations, sporting events and new services like CBeebies Radio.

We want to build a platform which is as future proof as we can make it, and which we can support and manage over its lifetimeWe may therefore need to turn off some formats in order to achieve this, but will look to minimise the impact on our users.

We researched the technology being used across the rest of the industry and selected the best combination as our primary stream type. For those who are interested this was:

AAC encoded for quality with 4 different bit rates to support everything from mobile devices up to the very highest quality sound

HTTP chunked for cost effective and resilient delivery and the ability to provide new audience facing features.

Audiences use a variety of mechanisms to listen to our audio streams. These include BBC iPlayer Radio (either on the web, on mobile phones or tablets), aggregator services which include BBC services alongside other stations (including UK Radio Player and Tunein) and connected devices (including internet radios and internet connected HiFis). The aggregators and devices had taken advantage of streams that we had previously published, but apart from a few exceptions we had very little information about who they were and how they were using the streams.

We therefore setup a team to identify and work with the aggregators and manufacturers to help them understand what we were doing and to migrate to the new services. The team worked through the information available, reached out to the industry in January of last year and started to communicate the changes that were coming. During this we confirmed that the HTTP chunked streams weren't going to work for all devices, so we decided to add another stream type, for live streams only, as backward compatibility for those devices.

We considered the options and decided on:

SHOUTcast as the delivery mechanism because it was widely supported by devices and reasonably reliable (although less so than HTTP chunks)

MP3 codec rather than AAC because that meant many of those devices which previously used WMA would still be able to playback our streams

128 kbps because that was a reasonable quality and we intended this stream for internet radios not mobile devices

We also decided to use our International streams (which don't contain sport or other rights restricted material) because the UK only restrictions on Shoutcast streams actually generated 33 times as many errors as successful streams with our CDN partners, which in turn generated a disproportionate cost for us.

For on-demand we already provide a large number of podcasts as MP3 files. We cannot provide other content as MP3 because that format provides no way for us to fulfill our obligations to protect the content for our rights holders. Consequently the only on-demand assets will be AAC HLS.

Over the course of the last 12 months or so Jim Simmons and his team have successfully built and rolled out this service, overcoming some very significant technical challenges along the way. We now have all our stations being delivered through Audio Factory with all the benefits that brings to the vast majority of our users, and have rolled out these changes with very minimal disruption to users up until we had to start switching some of the legacy formats off.

What happened next?

Many of you will have read Jim and Henry’s posts, and indeed many of you commented on them. In the two weeks since we did turn off WMA live streams and switch some users to our backward compatibility SHOUTcast MP3 streams we have had a great deal of feedback.

Broadly this feedback has broken down into:

  • Radio 3 HD Sound streams to high end audio equipment
  • Access to sports content on BBC 5 Live and BBC 5 Live Sports Extra
  • Loss of service to devices, especially devices used by the visually impaired
  • Concerns about the communication of these changes

Taking each of these in turn:

Radio 3 HD Sound streams to high end audio equipment

Based on your feedback we have temporarily reinstated the Radio 3 HD Sound in its previous format, encoded at 320kbps AAC and delivered by SHOUTcast.

This is only temporary, is only for this service, and is intended to allow manufacturers to implement the changes to support the new format (320kbps AAC delivered by HLS/MPEG DASH), without interrupting access to the Proms.

Sports content on BBC 5 Live and BBC 5 Live Sports Extra

Based on your feedback we have investigated, planned and started work on adding UK only versions of our backward compatibility streams that will include sport. This goes beyond the 12 stations we used to provide UK only versions for. We will make all 57 stations available, including all the national, nations and English local radio stations in these formats. We don’t have a concrete timeline on this but are working quickly to introduce this.

Loss of service to devices, especially devices used by the visually impaired

There are three types of devices we are dealing with:

1) Those that have already migrated to our new services

2) Those that are capable of migrating but have not yet

3) Those that cannot migrate

Taking these in order.

Devices that have migrated

These include our own BBC iPlayer Radio applications and comprise the vast majority of listening. These are working well and receiving a good service, although we are continuing to monitor the impact of the changes. This week we also resolved a related issue that was seriously affecting some Android devices with our new streams.

Devices that are capable of migrating but have not yet

We are continuing to meet with manufacturers, many of who are confident that they can migrate their devices to using the new streams. Some will probably wait until we can provide MPEG-DASH streams as well as HLS, which will be later this year. MPEG-DASH is a new industry standard format (rather than the existing proprietary formats), which is very similar to HLS and shares the benefits of that.

Devices that cannot migrate

Our backward compatible streams are intended to support as many as possible but if your device cannot migrate, I am genuinely sorry. The technical landscape has changed so much over the last ten years and the sheer number of different proprietary systems for delivering audio that have come and gone makes it simply impractical for us to try to continue to support all devices. We have been in contact with all the manufacturers that we are aware of, including those who have contacted us directly as they have become aware of this project. We know that there are some devices that do not work, as well as many that fit into the second category.

Concerns about the communication of these changes

This has actually been the most frequently stated concern and there are definitely lessons to be learnt from this process. It wasn’t as good as it could have been and I apologise for that.

Our intention in contacting the industry in January of 2014 was to start the process of migrating devices so that as few as possible were actually affected when the changes happened. Some manufacturers understood, responded to the information we provided, asked us questions, implemented the changes and those devices are now working fine.

Others did not, whether because the information wasn’t clear enough or for other reasons. We also didn’t know about all the people using our streams, for the reasons outlined above, so despite our attempts we didn’t get full coverage.

More manufacturers contacted us when Jim blogged in September about the WMA streams going away, but again there were still surprises.

In an attempt to reach users who were to be affected we also played out a recorded message on the affected WMA streams, but sadly many of the devices which were receiving those streams hadn’t implemented the required part of WMA and stopped working altogether so we had to withdraw the message. Right now we are about making sure as many people as possible are aware, including working with radio programmes such as Feedback and In Touch on Radio 4. We don’t intend to make a change of this scale again in the near future, but we have already started to review all the communication for this change with a view to avoiding the surprise of the last few weeks.

Despite these very genuine concerns I am pleased with the outcome of the Audio Factory project.

We have very high quality, reliable streams for all of our radio stations in a consistent format, which we can support moving forward. We also have the opportunity to enable new features for our audiences that are already available on iPlayer TV thanks to Video Factory. These include Live Restart, which jumps you back to the start of a programme if you tune in half way through; and DRM Downloads, which will allow offline listening for all programmes.

There are definitely lessons to learn from this project and I welcome your comments and feedback.


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