Using Audio jacks¶

The 335x provides an ALSA driver in the kernel for recording and playing audio files.

To learn more about ALSA you can read up on it here: http://www.alsa-project.org/main/index.php/Main_Page

Using ALSA tools to record/play wav files¶

Recording:

# Unmute the microphone
amixer set PCM 100 on || echo "Unable to set mixer control for PCM" 
# Record in dat file format for 3 seconds.
arecord -f dat -d 3 > test.wav || echo "Unable to run arecord" 

Playback:

# Unmute the speaker
amixer set PCM 100 on || echo "Unable to set mixer control for PCM" 
# Playback wav file
aplay test.wav || echo "aplay failed" 

Integrating with Application¶

Gstreamer is one possibility for integrating sound into your application.

Source: https://developer.ridgerun.com/wiki/index.php/LeopardBoard_GStreamer_Pipelines#Audio_Input

Recording:

# Record into mp4 format until canceled
gst-launch -e alsasrc ! 'audio/x-raw-int,rate=(int)44100,channels=(int)2' ! queue ! ffenc_aac bitrate=128000 ! qtmux ! filesink location=audio_aac.mp4

Playback:

gst-launch filesrc location=audio_aac.mp4 ! qtdemux ! ffdec_aac ! alsasink

If there are issues setting mixer levels with the ALSA tools, you can set the volume directly in the gst-launch command with the 'volume' element. The volume is set on a scale from '0' to '1' with '1' being 100% of the input level. Here's the same gst-launch playback command with the volume set to 50% of the original level.

gst-launch filesrc location=audio_aac.mp4 ! qtdemux ! ffdec_aac ! volume volume='0.5' ! alsasink

Note: gst-inspect can be used to identify what pipelines are available.

Read up on the following for more info on gstreamer: http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/

Audo playback linux applications¶

The following programs should be available to install via opkg.

• vlc - 1.1.4.1-r0.6 - Video player and streamer - davinci edition
• mplayer - 0.0+1.0rc3+svnr32735-r27.6 - Open Source multimedia player.
• madplay - 0.15.2b-r0.6 - Madplay is a command-line MPEG audio decoder and player
• ffmpeg - 2:0.6.1+r17.1+gitr0+0b32da90f893b3e04ead18a546252e241a6a0988-r17.1.6 - FFmpeg is a complete solution to record, convert and stream audio and video