Adding audio to the CCTV of your burgular

In a full on throw back to the 2nd ever post to this blog, back in February 2010, I’ve recently been updating the system that sends me a video when there is movement in my flat via MMS and email.

I thought I’d try and add audio to the video that gets sent. A quick Google turned up two options, one was to use the sox command and it’s silence option, the second uses the on_event_start triggers in motion as a way to record the audio at the same time as capturing the movement video. I went with the second option and tweaked it a bit to make it pick the right input for my system and to direct encode the audio to MP3 rather than WAV to save space.

on_event_start arecord --process-id-file /var/motion/arecord.pid -D sysdefault:CARD=AF -f S16_LE -r 22050 - | lame  -m m - /var/motion/%Y%m%d_%H%M%S.mp3

The other useful addition was the –process-id-file /var/motion/arecord.pid which writes the process id to a file so I can just use this to stop the recording rather than having to use grep and awk to find the process in the ps output.

on_event_end kill `cat /var/motion/arecord.pid`

Now it’s just a case of combining the video from motion with the audio. I can do this with ffmpeg when I re-encode the video into the 3gp container to make it suitable for sending via a MMS message.

ffmpeg -i movement.avi -i movement.mp3 -map 0:v -map 1:a -c:a aac -strict -2 -s qcif -c:v h263 -y /var/www/html/cam1/intruder.3gp

This seams to work but the output file is a little large. The default audio encoding seams to be at 160k bitrate, I wound it down to 32k and the file size got a lot better.

ffmpeg -i movement.avi -i movement.mp3 -map 0:v -map 1:a -c:a aac -b:a 32k -strict -2 -s qcif -c:v h263 -y /var/www/html/cam1/intruder.3gp

I’d like to try the AMR audio codec but I can’t get ffmpeg to encode with it at the moment, so I’m just going to email the mp3 of the audio along with the high res AVI version of the video and just send the low res 3GP version via MMS.