[英]Sink to the virtual v4l2 device
I have tried an example on Ubuntu 19.04我在 Ubuntu 19.04 上试过一个例子
gst-launch-1.0 videotestsrc ! v4l2sink device=/dev/video10
But gstreamer fails但是 gstreamer 失败了
Setting pipeline to PAUSED ...
ERROR: Pipeline doesn't want to pause.
ERROR: from element /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0: Cannot identify device '/dev/video10'.
Additional debug info:
v4l2_calls.c(609): gst_v4l2_open (): /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0:
system error: No such file or directory
Setting pipeline to NULL ...
Freeing pipeline ...
Why it doesn't work?为什么它不起作用? I haven't found this in the documentation, do I need to create /dev/video10 somehow?
我在文档中没有找到这个,我需要以某种方式创建 /dev/video10 吗?
I did the same for the default device /dev/video1, but it is an input camera device on my laptop:我对默认设备 /dev/video1 做了同样的事情,但它是我笔记本电脑上的输入摄像头设备:
sudo gst-launch-1.0 videotestsrc ! v4l2sink
Setting pipeline to PAUSED ...
ERROR: Pipeline doesn't want to pause.
ERROR: from element /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0: Device '/dev/video1' is not a output device.
Additional debug info:
v4l2_calls.c(639): gst_v4l2_open (): /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0:
Capabilities: 0x4a00000
Setting pipeline to NULL ...
Freeing pipeline ...
Thank in advance.预先感谢。
The title of your questions suggests you would like to write to a virtual video device.您的问题标题表明您想写入虚拟视频设备。 v4l2 devices can be both input and output video devices.
v4l2 设备既可以是输入视频设备,也可以是输出视频设备。 Your camera is a video input (capture) device.
您的相机是视频输入(捕获)设备。 Directing a v4l2sink (so an endpoint of the pipeline) in gstreamer will likely fail.
在 gstreamer 中引导 v4l2sink(因此是管道的端点)可能会失败。
You can however generate a virtual output device.但是,您可以生成虚拟输出设备。 What you are looking for is something like the v4l2-loopback device.
您正在寻找的是类似于v4l2-loopback设备的东西。 It allows you to generate a virtual
/dev/video10
device like this:它允许您像这样生成一个虚拟的
/dev/video10
设备:
modprobe v4l2loopback video_nr=10
Another possible solution for the same error message: recreate the v4l2loopback interface:相同错误消息的另一种可能解决方案:重新创建 v4l2loopback 接口:
sudo rmmod -f v4l2loopback
sudo modprobe v4l2loopback
This might apply to others experiencing the error message from the original question, but who are already aware they need a v4l2loopback device as gstreamer sink.这可能适用于遇到来自原始问题的错误消息的其他人,但已经知道他们需要 v4l2loopback 设备作为 gstreamer 接收器。
When trying to stream a video to the existing v4l2loopback device I streamed to using ffmpeg before, I got the same error message尝试将视频流式传输到我之前使用 ffmpeg 流式传输的现有 v4l2loopback 设备时,我收到了相同的错误消息
Device '/dev/video0' is not a output device.
设备“/dev/video0”不是输出设备。
Investigation调查
When comparing the state of a working loopback video device and a non-working one (ie after writing to it with ffmpeg) with v4l2-ctl --all -d 0
using diff
, I found the following difference :使用
diff
将工作环回视频设备和非工作环回视频设备的状态(即在使用 ffmpeg 写入后)与v4l2-ctl --all -d 0
进行diff
,我发现了以下差异:
--- working 2020-11-19 18:03:52.499440518 +0100
+++ non-working 2020-11-19 18:03:57.472802868 +0100
@@ -3,21 +3,18 @@
Card type : GPhoto2 Webcam
Bus info : platform:v4l2loopback-000
Driver version : 5.9.8
- Capabilities : 0x85208002
- Video Output
+ Capabilities : 0x85208000
Video Memory-to-Memory
Read/Write
Streaming
Extended Pix Format
Device Capabilities
- Device Caps : 0x05208002
- Video Output
+ Device Caps : 0x05208000
Video Memory-to-Memory
Read/Write
Streaming
Extended Pix Format
Priority: 0
-Video output: 0 (loopback in)
Format Video Output:
Width/Height : 960/640
Pixel Format : 'YU12' (Planar YUV 4:2:0)
Somehow that "Video Output" capability is required for gstreamer to work successfully and taken away by my previous ffmpeg call.不知何故,gstreamer 需要“视频输出”功能才能成功工作并被我之前的 ffmpeg 调用带走。 The behaviour only occured when I loaded the v4l2loopback module with the
exclusive_caps=1
option, see 1 .该行为仅在我使用
exclusive_caps=1
选项加载 v4l2loopback 模块时发生,请参阅1 。
The solution was to unload / load the v4l2loopback kernel commands, forcefully removing the v4l2loopback kernel module and adding it again using rmmod / modprobe (see above).解决方案是卸载/加载 v4l2loopback 内核命令,强行删除 v4l2loopback 内核模块并使用 rmmod / modprobe(见上文)再次添加它。
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