Input Devices
*************

Input devices are configured elements in FFmpeg which allow to access the data coming from a multimedia device attached to your system.

When you configure your FFmpeg build, all the supported input devices are enabled by default. You can list all available ones using the configure option "--list-indevs".

You can disable all the input devices using the configure option "--disable-indevs", and selectively enable an input device using the option "--enable-indev=INDEV", or you can disable a particular input device using the option "--disable-indev=INDEV".

The option "-formats" of the ff* tools will display the list of supported input devices (amongst the demuxers).

A description of the currently available input devices follows.

alsa
====

ALSA (Advanced Linux Sound Architecture) input device.

To enable this input device during configuration you need libasound installed on your system.

This device allows capturing from an ALSA device. The name of the device to capture has to be an ALSA card identifier.

An ALSA identifier has the syntax:

     hw:CARD[,DEV[,SUBDEV]]

where the DEV and SUBDEV components are optional.

The three arguments (in order: CARD,DEV,SUBDEV) specify card number or identifier, device number and subdevice number (-1 means any).

To see the list of cards currently recognized by your system check the files /proc/asound/cards and /proc/asound/devices.

For example to capture with ffmpeg from an ALSA device with card id 0, you may run the command:

     ffmpeg -f alsa -i hw:0 alsaout.wav

For more information see: http://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html

bktr
====

BSD video input device.

dv1394
======

Linux DV 1394 input device.

jack
====

JACK input device.

To enable this input device during configuration you need libjack installed on your system.

A JACK input device creates one or more JACK writable clients, one for each audio channel, with name CLIENT_NAME:input_N, where CLIENT_NAME is the name provided by the application, and N is a number which identifies the channel. Each writable client will send the acquired data to the FFmpeg input device.

Once you have created one or more JACK readable clients, you need to connect them to one or more JACK writable clients.

To connect or disconnect JACK clients you can use the jack_connect and jack_disconnect programs, or do it through a graphical interface, for example with qjackctl.

To list the JACK clients and their properties you can invoke the command jack_lsp.

Follows an example which shows how to capture a JACK readable client with ffmpeg.

     # Create a JACK writable client with name "ffmpeg".
     $ ffmpeg -f jack -i ffmpeg -y out.wav

     # Start the sample jack_metro readable client.
     $ jack_metro -b 120 -d 0.2 -f 4000

     # List the current JACK clients.
     $ jack_lsp -c
     system:capture_1
     system:capture_2
     system:playback_1
     system:playback_2
     ffmpeg:input_1
     metro:120_bpm

     # Connect metro to the ffmpeg writable client.
     $ jack_connect metro:120_bpm ffmpeg:input_1

For more information read: http://jackaudio.org/

libdc1394
=========

IIDC1394 input device, based on libdc1394 and libraw1394.

oss
===

Open Sound System input device.

The filename to provide to the input device is the device node representing the OSS input device, and is usually set to /dev/dsp.

For example to grab from /dev/dsp using ffmpeg use the command:

     ffmpeg -f oss -i /dev/dsp /tmp/oss.wav

For more information about OSS see: http://manuals.opensound.com/usersguide/dsp.html

video4linux and video4linux2
============================

Video4Linux and Video4Linux2 input video devices.

The name of the device to grab is a file device node, usually Linux systems tend to automatically create such nodes when the device (e.g. an USB webcam) is plugged into the system, and has a name of the kind /dev/videoN, where N is a number associated to the device.

Video4Linux and Video4Linux2 devices only support a limited set of WIDTHxHEIGHT sizes and framerates. You can check which are supported for example with the command dov4l for Video4Linux devices and the command v4l-info for Video4Linux2 devices.

If the size for the device is set to 0x0, the input device will try to autodetect the size to use.

Video4Linux support is deprecated since Linux 2.6.30, and will be dropped in later versions.

Follow some usage examples of the video4linux devices with the ff* tools.

     # Grab and show the input of a video4linux device.
     ffplay -s 320x240 -f video4linux /dev/video0

     # Grab and show the input of a video4linux2 device, autoadjust size.
     ffplay -f video4linux2 /dev/video0

     # Grab and record the input of a video4linux2 device, autoadjust size.
     ffmpeg -f video4linux2 -i /dev/video0 out.mpeg

vfwcap
======

VfW (Video for Windows) capture input device.

x11grab
=======

X11 video input device.

This device allows to capture a region of an X11 display.

The filename passed as input has the syntax:

     [HOSTNAME]:DISPLAY_NUMBER.SCREEN_NUMBER[+X_OFFSET,Y_OFFSET]

HOSTNAME:DISPLAY_NUMBER.SCREEN_NUMBER specifies the X11 display name of the screen to grab from. HOSTNAME can be ommitted, and defaults to "localhost". The environment variable DISPLAY contains the default display name.

X_OFFSET and Y_OFFSET specify the offsets of the grabbed area with respect to the top-left border of the X11 screen. They default to 0.

Check the X11 documentation (e.g. man X) for more detailed information.

Use the dpyinfo program for getting basic information about the properties of your X11 display (e.g. grep for "name" or "dimensions").

For example to grab from :0.0 using ffmpeg:

     ffmpeg -f x11grab -r 25 -s cif -i :0.0 out.mpg

     # Grab at position 10,20.
     ffmpeg -f x11grab -25 -s cif -i :0.0+10,20 out.mpg