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

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

When you configure your Libav 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 avconv from an ALSA device with card id 0, you may run the command:

     avconv -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.

fbdev
=====

Linux framebuffer input device.

The Linux framebuffer is a graphic hardware-independent abstraction layer to show graphics on a computer monitor, typically on the console. It is accessed through a file device node, usually /dev/fb0.

For more detailed information read the file Documentation/fb/framebuffer.txt included in the Linux source tree.

To record from the framebuffer device /dev/fb0 with avconv:

     avconv -f fbdev -r 10 -i /dev/fb0 out.avi

You can take a single screenshot image with the command:

     avconv -f fbdev -frames:v 1 -r 1 -i /dev/fb0 screenshot.jpeg

See also http://linux-fbdev.sourceforge.net/, and fbset(1).

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 Libav 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 avconv.

     # Create a JACK writable client with name "libav".
     $ avconv -f jack -i libav -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
     libav:input_1
     metro:120_bpm

     # Connect metro to the avconv writable client.
     $ jack_connect metro:120_bpm libav: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 avconv use the command:

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

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

pulse
=====

pulseaudio input device.

To enable this input device during configuration you need libpulse-simple installed in your system.

The filename to provide to the input device is a source device or the string "default"

To list the pulse source devices and their properties you can invoke the command pactl list sources.

     avconv -f pulse -i default /tmp/pulse.wav

SERVER AVOption
---------------

The syntax is:

     -server SERVER NAME

Connects to a specific server.

NAME AVOption
-------------

The syntax is:

     -name APPLICATION NAME

Specify the application name pulse will use when showing active clients, by default it is "libav"

STREAM_NAME AVOption
--------------------

The syntax is:

     -stream_name STREAM NAME

Specify the stream name pulse will use when showing active streams, by default it is "record"

SAMPLE_RATE AVOption
--------------------

The syntax is:

     -sample_rate SAMPLERATE

Specify the samplerate in Hz, by default 48kHz is used.

CHANNELS AVOption
-----------------

The syntax is:

     -channels N

Specify the channels in use, by default 2 (stereo) is set.

FRAME_SIZE AVOption
-------------------

The syntax is:

     -frame_size BYTES

Specify the number of byte per frame, by default it is set to 1024.

FRAGMENT_SIZE AVOption
----------------------

The syntax is:

     -fragment_size BYTES

Specify the minimal buffering fragment in pulseaudio, it will affect the audio latency. By default it is unset.

sndio
=====

sndio input device.

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

The filename to provide to the input device is the device node representing the sndio input device, and is usually set to /dev/audio0.

For example to grab from /dev/audio0 using avconv use the command:

     avconv -f sndio -i /dev/audio0 /tmp/oss.wav

video4linux2
============

Video4Linux2 input video device.

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.

Video4Linux2 devices usually support a limited set of WIDTHxHEIGHT sizes and framerates. You can check which are supported using -list_formats all for Video4Linux2 devices.

Some usage examples of the video4linux2 devices with avconv and avplay:

     # Grab and show the input of a video4linux2 device.
     avplay -f video4linux2 -framerate 30 -video_size hd720 /dev/video0

     # Grab and record the input of a video4linux2 device, leave the
     framerate and size as previously set.
     avconv -f video4linux2 -input_format mjpeg -i /dev/video0 out.mpeg

vfwcap
======

VfW (Video for Windows) capture input device.

The filename passed as input is the capture driver number, ranging from 0 to 9. You may use "list" as filename to print a list of drivers. Any other filename will be interpreted as device number 0.

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 avconv:

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

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

FOLLOW_MOUSE AVOption
---------------------

The syntax is:

     -follow_mouse centered|PIXELS

When it is specified with "centered", the grabbing region follows the mouse pointer and keeps the pointer at the center of region; otherwise, the region follows only when the mouse pointer reaches within PIXELS (greater than zero) to the edge of region.

For example:

     avconv -f x11grab -follow_mouse centered -r 25 -s cif -i :0.0 out.mpg

     # Follows only when the mouse pointer reaches within 100 pixels to edge
     avconv -f x11grab -follow_mouse 100 -r 25 -s cif -i :0.0 out.mpg

SHOW_REGION AVOption
--------------------

The syntax is:

     -show_region 1

If SHOW_REGION AVOption is specified with 1, then the grabbing region will be indicated on screen. With this option, it's easy to know what is being grabbed if only a portion of the screen is grabbed.

For example:

     avconv -f x11grab -show_region 1 -r 25 -s cif -i :0.0+10,20 out.mpg

     # With follow_mouse
     avconv -f x11grab -follow_mouse centered -show_region 1  -r 25 -s cif -i :0.0 out.mpg