Video

Introduction

Most cameras will output "raw video" but for streaming it is encoded with a format like mpeg or h.264 and wrapped in a container like avi, swf, or mp4. Encoding includes compression so the video doesn't consume huge amounts of bandwidth or disk space. Encoding the video can consume considerable processing power (40 to 100% CPU utilization). Underpowered machines are limited to low frame rates (5 fps) and resolutions (320x240) resulting in slow, jerky video. The Pi's core has encoder hardware but enabling it requires payment of a licensing fee.

Some cameras have hardware encoders built into the camera and in addition to raw video, can also stream encoded video. The Logitech HD920 has mpeg and h.264 encoders. If the camera will stream encoded video, essentially all the computer has to do is copy the video stream from the camera to the network interface which results in 2 to 5% CPU utilization.

Display camera modes

Video4Linux can be used to find out what formats the camera supports and to control the camera.

To install Video4Linux on the Pi:

apt-get install v4l-utils v4l-conf

To display the video formats the camera supports:

v4l2-ctl --list-formats

If the camera is fixed, auto focus can be turned off and the camera focused manually.

To turn auto focus off and manually set the focus:

/usr/bin/v4l2-ctl --verbose --set-ctrl=focus_auto=0
/usr/bin/v4l2-ctl -d 0 -c focus_absolute=25

Install ffmpeg

Ffmpeg is one program to encode or copy video and/or audio streams.

1. Install h.264 library libx264 if h.264 encoding will be used.

git clone git://git.videolan.org/x264.git
cd x264
./configure --enable-static --enable-shared *See Note 1 below.
make
make install
ldconfig

2. Install ffmpeg

git clone git://source.ffmpeg.org/ffmpeg.git
cd ffmpeg
./configure --enable-gpl --enable-libx264  --enable-libfreetype *See Note 2

make
make install
ldconfig

NOTES:
1. Disable the assembler when compiling on the Pi[1]:

./configure --disable-asm --enable-shared

2. Disable mmx when compiling on the Pi

./configure --enable-shared --enable-gpl  --enable-libx264   --enable-libfreetype --disable-mmx