From 39140979070b03f3afe656ac78a982463fd82e2b Mon Sep 17 00:00:00 2001
From: tiyn <tiyn@posteo.eu>
Date: Tue, 18 Mar 2025 05:52:33 +0100
Subject: [PATCH] obs/v4l2: added troubleshooting for error

---
 wiki/linux/package_manager.md | 13 +++++++++++++
 wiki/linux/v4l2.md            | 20 ++++++++++++++++++++
 wiki/obs.md                   | 17 +++++++++++++----
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/wiki/linux/package_manager.md b/wiki/linux/package_manager.md
index f4f19d5..4c3142f 100644
--- a/wiki/linux/package_manager.md
+++ b/wiki/linux/package_manager.md
@@ -19,6 +19,19 @@ It features the same syntax.
 
 This section addresses various usages of the arch linux package managers.
 
+### Downgrading Packages 
+
+Packages of the AUR can be downgraded by using the
+[Downgrade](https://github.com/archlinux-downgrade/downgrade) program.
+This program can then easily be used to an AUR package.
+This works like the following assuming the package `v4l2loopback-dmks` needs to be downgraded.
+
+```sh 
+sudo downgrade v4l2loopback-dmks
+```
+
+Afterwards the target version can be selected and the downgrading process will conclude.
+
 #### Manual Installation of a `PKGBUILD` File
 
 A `PKGBUILD` file is a [shell](/wiki/linux/shell.md) script that contains the installation 
diff --git a/wiki/linux/v4l2.md b/wiki/linux/v4l2.md
index 9d80019..aab788b 100644
--- a/wiki/linux/v4l2.md
+++ b/wiki/linux/v4l2.md
@@ -21,6 +21,11 @@ package needs to be installed.
 Some distributions have a package named `v4l2loopback-dkms` in the package
 manager, making the manual installation process unnecessary.
 
+Make sure to
+[start the service](/wiki/linux/systemd.md#startstopenabledisable-a-service) by
+running `systemctl start v4l2loopback.service` and/or enable it to start after each
+boot with `systemctl enable v4l2loopback.service`.
+
 ### Usage
 
 This section focusses on various use-cases for the v4l2loopback software.
@@ -75,3 +80,18 @@ Afterwards enable the service to start at every boot process by running:
 ```sh
 sudo systemctl enable v4l2loopback
 ```
+
+## Troubleshooting
+
+This section focusses on various errors that can appear in the v4l2loopback software.
+
+### `Failed to start streaming on '/dev/video2' (Invalid argument)`
+
+This error does occur most of the time when trying to start
+[OBS' virtual camera](/wiki/obs.md#virtual-camera).
+This section is based on an
+[OBS Forum entry by rebelduck](https://obsproject.com/forum/threads/obs-virtual-camera-failed-to-start-streaming-on-dev-video2-invalid-argument.184717/)
+To fix it downgrade the packages `v4l2loopback-dkms` and `v4l2loopback-utils` to the last working
+version.
+For [Arch Linux](/wiki/linux/arch-linux.md) this can be achieved by using
+[Downgrade](/wiki/linux/package_manager.md#downgrading-packages).
diff --git a/wiki/obs.md b/wiki/obs.md
index b61ca77..a436e34 100644
--- a/wiki/obs.md
+++ b/wiki/obs.md
@@ -20,10 +20,6 @@ camera.
 First of all [V4L2](./linux/v4l2.md) needs to be set up.
 This guide assumes it is set up according to the section in the
 [V4L2 entry](./linux/v4l2.md#v4l2loopback).
-Make sure to
-[start the service](/wiki/linux/systemd.md#startstopenabledisable-a-service) by
-running `systemctl start v4l2loopback.service` or enable it to start after each
-boot with `systemctl enable v4l2loopback.service`.
 Afterwards the virtual camera can be started.
 
 ### Background Removal
@@ -39,3 +35,16 @@ describes various possibilities to install the background removal for OBS on
 different systems.
 On Linux systems background removal is often contained in a package named
 `obs-backgroundremoval` or similarly.
+
+## Troubleshooting
+
+This section focusses on various errors that can appear by using OBS.
+
+### `Output Failed: If you are using NVENC or AMD encoders, make sure the video drivers are up to date`
+
+This error does occur most of the time when trying to start
+[OBS' virtual camera](/wiki/obs.md#virtual-camera).
+If all the drivers are up to date there is a chance that it is caused by a bug or error in the code
+of [V4L2](/wiki/linux/v4l2.md).
+A possible fix is described in a 
+[corresponding section of the V4L2 entry](/wiki/linux/v4l2.md#failed-to-start-streaming-on-devvideo2-invalid-argument).