AudioEngine

Template:Frodo

AudioEngine (or AE) refers to XBMC's new audio system, a two-year project spear-headed by gnif which is intended to be released in v12 (Frodo), and has been merged with master for user testing as of May 15th, 2012. Why a new audio subsystem?

It's been an accepted fact that the existing audio code was little-touched since the early days of XBMC, and was limited by the 16-bit architecture of the original XBox and codecs available at the time. Dolby AC3 and mp3 (or earlier formats!) ruled the media codec world. Over time HTPC's became more mainstream, more powerful and better connected. Analog gave way to optical SPDIF connections, in turn replaced with HDMI. Processors, GPU's and media formats evolved at a steady pace.

With the growth of the HTPC and new formats like those made available with Bluray technology, the audio subsystem was under scrutiny as an area for improvement. Higher definition audio like multichannel FLAC was becoming a preferred standard for those demanding higher quality audio media. It was time for an update, and what an update!

History and Team

Early efforts at patching fixes and even an initial attempt at a completely new system fell by the wayside. The scope of the required changes and the complexity of the API made it a daunting task, especially for volunteer programmers working in their spare time. This was compounded by the fact that XBMC runs on a wide range of hardware and operating systems. Most of the developers focus on specific platforms or subsystems within the whole of XBMC. Any new system had to be platform-agnostic, cohesive and flexible.

In time, it became obvious the project was going to require a full re-write and replacement of the audio engine. Furthermore, XBMC's base of hardware and OS platforms continued to grow. The detailed specifications for the new audio formats were unknown, and of course the master code for XBMC was ever-changing.

In November of 2009 gnif decided to bite the proverbial bullet, and after extensive consultation with the team finalized the API or structure which was to become AE. Drawing in other developers as required, the massive project slowly took shape, and reached the ready-point for user tests a year later. The forum thread for those hardy beta-testers (thank you!) reached over 1,200 posts, and slowly but surely features were added and debugged, and system stability grew.

Over the next two years, thanks to the determination of gnif the core engines, decoders, encoders and utilities that make up AudioEngine became a reality, and other developers began to contribute to the core and especially the platform-specific sinks or output stages. Among those contributing were gimli, fneufneu, memphiz, dddamian, anssi and others.

There was a goal to have the new audio system ready for Eden 11.0, but there was just too much left to do. Many users were eagerly looking forward to it's inclusion, but stable releases must continue, and AE wasn't ready when the Eden feature-freeze went into effect. During this time the AE code-base was solidified, bugs tracked and squashed, features added and testing increased.

On May 15th 2012, AudioEngine was merged to master. Weighing in at over 22,000 lines of code, it represents one of the single biggest code-merges ever for XBMC. Now for the first time it is readily accessible for all the development team (and users!) to see, test and improve within the greater context of XBMC's master branch.

Team XBMC is proud to at last unveil AudioEngine, bringing HD audio to XBMC!

Features

Features of AE include

• support for DTS-MA / Dolby TrueHD Bluray formats
• support for 24-bit and floating-point audio at up to 384,000hz
• mixing of all streams including GUI sounds even when transcoding audio
• start-up enumeration of hardware audio devices and their capabilities with log output
• bitstreaming support in PAPlayer (XBMC's music player)
• upmixing of stereo to full channel layout
• tighter syncing of A/V streams
• floating-point processing of audio
• 24-bit and floating-point decoding/handling of mp3
• full support for ReplayGain
• built-in sample-rate conversion and transcoding

Planned Features for upcoming AE releases

• rules-based decisions for output formats based on hardware capabilities
• a range of DSP's (digital signal processors) including headphone head-related transfer function processing, DRC (dynamic range compression), low-pass filtering for subs and an equalizer function
• custom channel-mixing/mapping for up and downmixing

It's still early days for AE. Bugs will be found, and new and exciting features added. If you want to give it a try just grab one of the nightly versions on one of XBMC's mirrors.

AudioEngine replaces SDL and brings some of the external dependencies into XBMC, and wraps up all the different media types for mixing, samplerate conversion, format conversion, encoding, upmix, downmix, etc.

GUI Settings

AE brings several new settings to the graphical user interface (GUI) as well as to advancedsettings.xml.

Settings -> System -> Audio output

Audio output

Allows you to tell xbmc about the type of connection to the audio equipment. Optical/Coax and HDMI enable the passthrough of Dolby Digital and DTS to capable receivers.

Speaker Configuration

select your physical speaker layout

Boost volume level on downmix

Boosts AC3 streams that have been mixed-down to 2 channels

- Dolby Digital (AC3) capable receiver

Select this option if your receiver is capable of decoding AC3 streams.

- DTS capable receiver

Select this option if your receiver is capable of decoding DTS streams.

- AAC capable receiver

Select this option if your receiver is capable of decoding AAC streams.

- MultiChannel LPCM capable receiver

Select this option if your receiver is capable of decoding LPCM streams.

- TrueHD capable receiver

Select this option if your receiver is capable of decoding TrueHD streams.

- DTS-HD capable receiver

Select this option if your receiver is capable of decoding DTS-HD streams.

Audio output device

device you use to play PCM or decoded audio such as mp3's and FLAC.

Passthrough output device

device you use to play encoded formats (those checked in "xyz capable receiver" above).

Play GUI sounds

Interface sounds. Select from never, only when playback stopped, or always.

---

Settings -> Music -> Playback

Here you can find the settings for ReplayGain and Cross-Fading music (gapless playback).

Play the next song automatically

XBMC automatically plays the next item in the current folder. For example, in Files View: After a track has been played, XBMC would automatically play the next track in the same folder.

Queue songs on selection

When songs are added to a playlist they are queued instead of playback starting immediately.

Replaygain volume adjustments

When enabled, XBMC will read the Replay Gain information encoded in your audio files by a program such as MP3Gain and normalize the sound levels accordingly. You have the option of either using track levels or album levels.

PreAmp Level - Replay gained files

level in dB - default is 89dB per standard

PreAmp Level - Non replay gained files

level in dB - default is 89dB per standard

Avoid clipping on replay gained files

reduce volume of the file if clipping is likely to occur

Crossfade between songs

Enabling this will cause the player to smoothly fade from one audio track to the next. You can set the amount of overlap of the tracks from 1-10 seconds.

Crossfade between songs on the same album

You have the option of only crossfading between songs on the same album or all.

Visualization

Determines which visualization will be displayed while listening to music. For more information, see Visualizations.

Advanced settings

Current advancedsettings.xml tags for AE:

 <advancedsettings>
   <audio>
     <resample>0</resample>
     <forceDirectSound>0</forceDirectSound>
     <audiophile>0</audiophile>
     <audiosinkbufferdurationmsec>50</audiosinkbufferdurationmsec>
     <allowtranscode44100>0</allowtranscode44100>
     <streamsilence>0</streamsilence>
   </audio>
 </advancedsettings>

Default values are shown above in the code box - these values are used if that tag does not exist.

resample	force resampling of audio at a given frequency e.g. 48000 = 48khz
forceDirectSound	win-specific - will not use Wasapi API 0 = false, 1 = true
audiophile	forces playback of original format, will not down/upmix next song to match current, not compatible with cross-fading 0 = false, 1 = true
audiosinkbufferdurationmsec	win-specific, buffer time in msec, hard minimum of 50msec
allowtranscode44100	allows 44100hz when trancoding for SPDIF devices 0=false, 1=true
streamsilence	forces original AE behaviour where an audio signal is constantly streamed to the audio device, even if silent. If 1 or true, This prevents some receivers from losing the signal/source, and prevents sinks re-opening and possible receiver switching with each new stream after any silence. If 0 or false, enables Eden-style releasing of the audio device so external players, programs and the system can access the audio device, i.e. prevents XBMC from hogging the audio device.

Hardware reported to work

Please add your experience

Model Name	GPU Name	GPU Code Name	DTS-MA	Dolby True HD	Dolby Digital Plus	Video Driver Version	Operating System
Asus EN210	Nvidia G210	GT218	Yes	Yes	No	302.17	Ubuntu 11.10
Asus EN210	Nvidia G210	GT218	Yes	Yes	-	290.10	Ubuntu 12.04 LTS
Asus ENGT430 DC SL DI 1GD3	Nvidia GT 430	GF108	Yes	Yes	-	295.59	Ubuntu 12.04 LTS
Asus ENGTX560	Nvidia GTX 560TI	GF110	Yes	Yes	-	304.43	Ubuntu 12.04 LTS
Palit GT640 1GB	Nvidia GT 640	GK107	Yes	Yes	-	304.43	Ubuntu 12.04 LTS
AMD A4-3400 APU	Radeon HD 6410D	-	Yes	Yes	testing	5.12.0.13	Windows 8 RTM
AMD A8-3870K APU	Radeon HD 6550D	-	No	No	-	12.1	Ubuntu 12.04 LTS
AMD A8-3870K APU	Radeon HD 6550D	-	Yes	Yes	-	12.4	Windows 7 x64 Pro

Support

The best place to get support for AE-related issues is the XBMC forum. Several threads exist - reading them will often answer any issues, and of course you can receive assistance there:

• Main AE forum thread
• Windows AE forum thread
• Linux AE forum thread
• GitHub Development Branch (outside master)

See also

• Windows audio APIs