Statistics
| Branch: | Revision:

ffmpeg / doc / indevs.texi @ c32ccf7c

History | View | Annotate | Download (6.14 KB)

1
@chapter Input Devices
2
@c man begin INPUT DEVICES
3

    
4
Input devices are configured elements in FFmpeg which allow to access
5
the data coming from a multimedia device attached to your system.
6

    
7
When you configure your FFmpeg build, all the supported input devices
8
are enabled by default. You can list them using the configure option
9
"--list-indevs".
10

    
11
You can disable all the input devices using the configure option
12
"--disable-indevs", and selectively enable an input device using the
13
option "--enable-indev=@var{INDEV}", or you can disable a particular
14
input device using the option "--disable-indev=@var{INDEV}".
15

    
16
The option "-formats" of the ff* tools will display the list of
17
supported input devices (amongst the demuxers).
18

    
19
A description of the currently available input devices follows.
20

    
21
@section alsa
22

    
23
ALSA (Advanced Linux Sound Architecture) input device.
24

    
25
To enable this input device during configuration you need libasound
26
installed on your system.
27

    
28
This device allows to capture from an ALSA device. The name of the
29
device to capture has to be an ALSA card identifier.
30

    
31
An ALSA identifier has the syntax:
32
@example
33
hw:@var{CARD}[,@var{DEV}[,@var{SUBDEV}]]
34
@end example
35

    
36
where the @var{DEV} and @var{SUBDEV} components are optional.
37

    
38
The three arguments (in order: @var{CARD},@var{DEV},@var{SUBDEV})
39
specify card number or identifier, device number and subdevice number
40
(-1 means any).
41

    
42
To see the list of cards currently recognized by your system check the
43
files @file{/proc/asound/cards} and @file{/proc/asound/devices}.
44

    
45
For example to capture with @file{ffmpeg} from an alsa device with
46
card id 0, you may run the command:
47
@example
48
ffmpeg -f alsa -i hw:0 alsaout.wav
49
@end example
50

    
51
For more information see:
52
@url{http://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html}
53

    
54
@section audio_beos
55

    
56
BeOS audio input device.
57

    
58
@section bktr
59

    
60
BSD video input device.
61

    
62
@section dv1394
63

    
64
Linux DV 1394 input device.
65

    
66
@section jack
67

    
68
Jack input device.
69

    
70
To enable this input device during configuration you need libjack
71
installed on your system.
72

    
73
A jack input device creates one or more jack writable clients, one for
74
each audio channel, with name @var{client_name}:input_@var{N}, where
75
@var{client_name} is the name provided by the application, and @var{N}
76
is a number which identifies the channel.
77
Each writable client will send the acquired data to the FFmpeg input
78
device.
79

    
80
Once you have created one or more jack readable clients, you need to
81
connect them to one or more jack writable clients.
82

    
83
To connect or disconnect jack clients you can use the
84
@file{jack_connect} and @file{jack_disconnect} programs, or do it
85
through a graphical interface, for example with @file{qjackctl}.
86

    
87
To list the jack clients and their properties you can invoke the command
88
@file{jack_lsp}.
89

    
90
Follows an example which shows how to capture a jack readable client
91
with @file{ffmpeg}.
92
@example
93
# create a jack writable client with name "ffmpeg"
94
$ ffmpeg -f jack -i ffmpeg -y out.wav
95

    
96
# start the sample jack_metro readable client
97
$ jack_metro -b 120 -d 0.2 -f 4000
98

    
99
# list the current jack clients
100
$ jack_lsp -c
101
system:capture_1
102
system:capture_2
103
system:playback_1
104
system:playback_2
105
ffmpeg:input_1
106
metro:120_bpm
107

    
108
# connect metro to the ffmpeg writable client
109
$ jack_connect metro:120_bpm ffmpeg:input_1
110
@end example
111

    
112
For more information read:
113
@url{http://jackaudio.org/}
114

    
115
@section libdc1394
116

    
117
IIDC1394 input device, based on libdc1394 and libraw1394.
118

    
119
@section oss
120

    
121
Open Sound System input device.
122

    
123
The filename to provide to the input device is the device node
124
representing the OSS input device, and is usually set to
125
@file{/dev/dsp/}.
126

    
127
For example to grab from @file{/dev/dsp/} using @file{ffmpeg} use the
128
command:
129
@example
130
ffmpeg -f oss -i /dev/dsp /tmp/oss.wav
131
@end example
132

    
133
For more information about OSS see:
134
@url{http://manuals.opensound.com/usersguide/dsp.html}
135

    
136
@section video4linux and video4linux2
137

    
138
Video4Linux and Video4Linux2 input video devices.
139

    
140
The name of the device to grab is a file device node, usually Linux
141
systems tend to automatically create such nodes when the device
142
(e.g. an USB webcam) is plugged to the system, and has a name of the
143
kind @file{/dev/video@var{N}}, where @var{N} is a number associated to
144
the device.
145

    
146
Video4Linux and Video4Linux2 devices only support a limited set of
147
@var{width}x@var{height} sizes and framerates. You can check which are
148
supported for example using the command @file{dov4l} for Video4Linux
149
devices, and the command @file{v4l-info} for Video4Linux2 devices.
150

    
151
If the size for the device is set to 0x0, the input device will
152
try to autodetect the size to use.
153

    
154
Video4Linux support is deprecated since Linux 2.6.30, and will be
155
dropped in later versions.
156

    
157
Follow some usage examples of the video4linux devices with the ff*
158
tools.
159
@example
160
# grab and show the input of a video4linux device
161
ffplay -s 320x240 -f video4linux /dev/video0
162

    
163
# grab and show the input of a video4linux2 device, autoadjust size
164
ffplay -f video4linux2 /dev/video0
165

    
166
# grab and record the input of a video4linux2 device, autoadjust size
167
ffmpeg -f video4linux2 -i /dev/video0 out.mpeg
168
@end example
169

    
170
@section vfwcap
171

    
172
VFW (Video For Window) catpure input device.
173

    
174
@section x11grab
175

    
176
X11 video input device.
177

    
178
This device allows to capture a region of an X11 display.
179

    
180
The filename passed in input has the syntax:
181
@example
182
[@var{hostname}]:@var{display_number}.@var{screen_number}[+@var{x_offset},@var{y_offset}]
183
@end example
184

    
185
@var{hostname}:@var{display_number}.@var{screen_number} specifies the
186
X11 display name of the screen to grab from. @var{hostname} can be not
187
specified, and defaults to "localhost". The environment variable
188
@env{DISPLAY} contains the default display name.
189

    
190
@var{x_offset} and @var{y_offset} specify the offsets of the grabbed
191
area with respect to the top/left border of the X11 screen image. They
192
default to 0.
193

    
194
Check the X11 documentation (e.g. man X) for more detailed information.
195

    
196
Use the @file{dpyinfo} program for getting basic information about the
197
properties of your X11 display screen (e.g. grep for "name" or
198
"dimensions").
199

    
200
For example to grab from @file{:0.0} using @file{ffmpeg}:
201
@example
202
ffmpeg -f x11grab -r 25 -s cif -i :0.0 out.mpg
203

    
204
# grab at position 10,20
205
ffmpeg -f x11grab -25 -s cif -i :0.0+10,20 out.mpg
206
@end example
207

    
208
@c man end INPUT DEVICES