Playing a sound file encoded in Dolby Digital 5.1 is doable with Raspberry Pi 2's quad-core processor that runs at 900MHz. In this instructable, a media player called MPLAYER will be used to decode sound encoded in Dolby Digital 5.1 and send the 6 channels of audio to an ALSA Virtual Device. The ALSA Virtual Device downmixes the 6 channels of audio into 2 channels as the Raspberry Pi's build-in sound chip support only stereo (2 channels: LEFT and RIGHT).
This instructable will cover the following:
- Play Dolby Digital 5.1 Audio and send 6 channels to ALSA Virtual Device that downmix es 5.1 channel sound to 2.0
- Create a virtual device that downmix 5.1 channel sound to 2.0
- Install Advanced Linux Sound Architecture (ALSA) utilities
- Use ALSA utilities to test sound card and sound device
This instructables will NOT cover the following
- Open Sound System (OSS)
My Raspberry Pi:
- Raspberry Pi 2 model
- Raspbian based on Debian Version 8.0 (a.k.a Jessie)
- Advanced Linux Sound Architecture Driver Version k4.1.10-v7+
- Pulse Audio and OSS are NOT installed
- 2 speakers connected to Raspberry Pi's audio/video 3.5mm socket.
Dolby Digital 5.1 Logo is the trademark of Dolby Laboratories.
Step 1: Test That Raspberry Pi's Built-in Sound Card and the Speakers Work
Complete the steps in "Test Sound Card and Speakers in Raspberry Pi".
Step 2: Create a ALSA Virtual Device That Downmixes 5.1 Channel Audio to 2.0 Channel
Complete the steps in "Make a Custom Sound Device that Downmix 5.1 channel to 2.0 Channel in Raspberry Pi" instructable.
Step 3: Install MPLAYER Software
sudo apt-get update
sudo apt-cache show mplayer2
Read the description of mplayer.
sudo apt-get install mplayer2
Step 4: Test ALSA Virtual Device Downmixes 6 Channel to 2 Channel Audio
The MPLAYER is expected to decode sound stream in encoded in Dolby Digital 5.1 and send 6 channels to ALSA Virtual Device. Alsa Virtual Device will downmix the 6 channel of audio to 2 channels.
Download the media file (dolbyaurora.vob) that I have upladed.
Change directory to where the media file (dolbyaurora.vob) was saved.
mplayer --ac=a52 --channels=6 -ao alsa:device=51to20 dolbyaurora.vob
You should see the video as shown in the screenshot and more importantly hear the audio.