Raspberry Pi A, Руководство пользователя, Страница: 259 / 314

C H A P T E R 1 5
T H E R A S P B E R R Y P I C A M E R A M O D U L E
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Other options supported by
raspistill
are also supported by
raspivid
. For example, to
set the width and height of the recorded video to 1,920x1,080—Full HD—use the
-w
and
-h
options as in the following command:
raspivid -w 1920 -h 1080 -o fullhdvideo.h264
To record a longer video, adjust the
-t
option by specifying your required length of video in
milliseconds. To record a minute of video, type the following command:
raspivid -t 6000 -o minutelongvideo.h264
TIP
Although h.264 is a reasonably efficient video format, recording at high resolutions can take up
considerable disk space. If you’re recording longer videos, be sure that you have enough free
space on your SD card or consider connecting a USB storage device like an external hard drive.
You can read more options for
raspivid
in Appendix B, “Camera Module Quick Reference”
or see a list of available options with the following command:
raspivid --help
Command-Line Time-Lapse Photography
So far, you’ve learned the basics of how to use the Raspberry Pi Camera Module—now it’s
time to find a practical use for the project. The key advantage of the Raspberry Pi over a
dumb network-connected camera is the capability to be easily programmed for different
tasks. In this example, you can turn your Raspberry Pi and connected Camera Module into a
time-lapse photography system.
The
raspistill
program comes with an option for enabling a time-lapse mode,
-tl
, which
continuously captures pictures according to a customisable delay in milliseconds. This fea-
ture is designed for when
raspistill
is called by an external program, such as a web server
or video streamer, and will overwrite the output file each time a new picture is taken.
To use
raspistill
in traditional time-lapse photography, where a new file is created each
time, you’ll need a way of driving
raspistill
externally. This could be a Python program, a
dedicated application or even a web server thread, but the easiest way is to use a process
known as
shell scripting .