Editing Video4Linux

{{Short description|Device drivers for real-time video capture}}
{{Infobox software
| name                   = Video4Linux
| title                  = Video4Linux
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| frequently updated     = <!-- DO NOT include this parameter unless you know what it does -->
| programming language   = [[C (programming language)|C]]
| operating system       = [[Linux]]
| platform               = [[Linux kernel]]
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| repo                   = {{URL|https://git.linuxtv.org/v4l-utils.git}} 
| license                = [[GNU General Public License]]
| website                = {{URL|http://www.linuxtv.org/}}
}}
'''Video4Linux''' ('''V4L''' for short) is a collection of [[device driver]]s and an [[application programming interface|API]] for supporting realtime [[video capture]] on [[Linux]] systems.<ref>{{cite web |url=https://fosdem.org/2014/schedule/event/v4l_intro/ |title=An Introduction to the Video4Linux Framework: How to write a video capture driver |date=2014-02-02 |access-date=2014-02-16}}</ref> It supports [[USB]] [[webcam]]s, [[TV tuner card|TV tuners]], [[Camera Serial Interface|CSI]] cameras, and related devices, standardizing their output, so programmers can easily add video support to their applications.

Video4Linux is responsible for creating V4L2 device nodes aka a device file (/dev/videoX, /dev/vbiX and /dev/radioX) and tracking data from these nodes. The device node creation is handled by V4L device drivers using the video_device struct (v4l2-dev.h) and it can either be allocated dynamically or embedded in another larger struct.

Video4Linux was named after [[Video for Windows]] (which is sometimes abbreviated "V4W"), but is not technically related to it.<ref>{{cite web |url=https://www.kernel.org/doc/Documentation/video4linux/v4l2-framework.txt |title=Overview of the V4L2 driver framework |access-date=2013-12-04 |url-status=dead |archive-url=https://web.archive.org/web/20140221165356/https://www.kernel.org/doc/Documentation/video4linux/v4l2-framework.txt |archive-date=2014-02-21 }} Overview of the V4L2 driver framework.</ref><ref>{{cite web| url=https://events.linuxfoundation.org/images/stories/pdf/lceu2012_debski.pdfVideo4Linux2 | title=Path to a Standardized Video Codec API |archive-url=https://web.archive.org/web/20140106032317/https://events.linuxfoundation.org/images/stories/pdf/lceu2012_debski.pdf |archive-date=2014-01-06 }}</ref>

While Video4Linux is only available on Linux, there is a compatibility layer available for [[FreeBSD]] called Video4BSD. This provides a way for many programs that depend on V4L to also compile and run on the FreeBSD operating system.

== History ==
V4L had been introduced late into the 2.1.X development cycle of the Linux kernel. Retroactively being renamed to V4L1, it was dropped in kernel 2.6.38.<ref>{{Cite web |title=gspca - LinuxTVWiki |url=https://linuxtv.org/wiki/index.php/Gspca |access-date=2024-01-12 |website=[[LinuxTV]]}}</ref>

V4L2 is the second version of V4L. Video4Linux2 fixed some design bugs and started appearing in the 2.5.x kernels. Video4Linux2 drivers include a compatibility mode for Video4Linux1 applications, though the support can be incomplete and it is recommended to use Video4Linux1 devices in V4L2 mode. The project DVB-Wiki is now hosted on [[LinuxTV]] web site.<ref>{{Cite web |last=Schimek |first=Michael H |title=Video for Linux Two API Specification |url=https://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec-single/v4l2.html |access-date=2024-01-12 |website=[[LinuxTV]]}}</ref>

Some programs support V4L2 through the [[media resource locator]] <code>v4l2://</code>.

== Software support ==
{{div col|colwidth=20em}}
* [[aMSN]]
* [[Cheese (software)]]
* [[Cinelerra]]
* [[CloudApp]]
* [[Ekiga]]
* [[FFmpeg]]
* [[FreeJ]]
* [[GStreamer]]
* [[Guvcview]]
* [[kdetv]]
* [[Kopete]]
* [[Libav]]
* [[Linphone]]
* [[LiVES]]
* motion
* [[MPlayer]]
* [[mpv (media player)|mpv]]
* [[MythTV]]
* [[Open Broadcaster Software]]<ref>{{Cite web|url=https://obsproject.com/|title=Open Broadcaster Software &#124; OBS|website=obsproject.com}}</ref>
* [[OpenCV]]
* [[Peek (software)|Peek]]
* [[PyGame]]
* [[Simple DirectMedia Layer|SDL3]]<ref>{{Cite web|url=https://github.com/libsdl-org/SDL/pull/5477|title=Add video capture API proposal by 1bsyl|website=[[GitHub]] }}</ref>
* [[Skype]]
* [[Tvheadend]]
* [[VLC media player]]
* [[xawtv]]
* [[Xine]]
* [[ZoneMinder]]
{{div col end}}

== Criticism ==
Video4Linux has a complex negotiation process, which caused not all applications having support for all cameras.<ref>{{Cite web |last=Corbet |first=Jonathan |date=2019-07-25 |title=Access to complex video devices with libcamera |url=https://lwn.net/Articles/794555/ |access-date=2023-02-06 |website=[[LWN.net]]}}</ref>

== See also ==
* [[Direct Rendering Manager]] – defines a kernel-to-user-space interface for access to graphics rendering and video acceleration
* [[Mesa 3D]] – implements video acceleration APIs

== References ==
{{Reflist|2}}

== External links ==
*[https://git.linuxtv.org/media_tree.git/tree media_tree] development git
*[https://git.linuxtv.org/v4l-utils.git/tree v4l-utils] development git
*[https://linuxtv.org/downloads/v4l-dvb-apis/ Linux Media Infrastructure API (V4L2, DVB and Remote Controllers)]
*[https://www.linuxtv.org/wiki/index.php/Main_Page Video4Linux-DVB wiki]
* [http://www.exploits.org/v4l Video4Linux resources]
* [http://video4bsd.sourceforge.net/ Video4BSD], a Video4Linux emulation layer
* [https://web.archive.org/web/20110707012535/http://alumnos.elo.utfsm.cl/~yanez/video-for-linux-sample-programs/ Video For Linux (V4L) sample applications]
* [https://web.archive.org/web/20110707012738/http://alumnos.elo.utfsm.cl/~yanez/video-for-linux-2-sample-programs/ Video For Linux 2 (V4L2) sample application]
* [https://archive.today/20130103002424/http://v4l4j.googlecode.com/ Access Video4Linux devices from Java]
* [https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/log/?qt=grep&q=v4l kernel.org]
* [http://wiki.openwrt.org/doc/howto/usb.video OpenWrt Wiki]
* [http://www.ideasonboard.org/uvc/ Linux UVC driver and tools], [[USB video device class]] (UVC)

{{Linux kernel}}

[[Category:Digital television]]
[[Category:Free video software]]
[[Category:Interfaces of the Linux kernel]]
[[Category:Linux drivers]]
[[Category:Linux kernel features]]
[[Category:Television technology]]