vlc and webcams with internal h264 encoder

[burek]

Hi,

I've got an usb webcam with internal (hardware) h264 encoder and I managed to start the stream using:

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vlc v4l2:///dev/video0:width=320:height=240:chroma=h264

So far, so good, but... The default bitrate, at which the webcam's h264 encoder is encoding the video stream, is too high for me (around 3-4 mbps) and I'd like to lower it down by telling the webcam to encode the video with a different bitrate. I don't want to transcode the stream with vlc, because in that case, there is no purpose of webcam's internal encoder.

I've been told (at the #v4l irc channel) that this can be done using ioctl() in vlc's source code (more info here, if needed: https://ffmpeg.org/trac/ffmpeg/ticket/1389 ), so my question is: is there a way to tell the webcam to lower the encoding bitrate, using vlc?

Thanks in advance.

[Rémi Denis-Courmont]

VLC can change the V4L2 controls via the command line or UI effects dialog. There is no support for UVC-specific functionality at this point in time.

So if the encoding parameters are not available as V4L2 controls, then it will not work as is.

[madrugado]

Hi all.

I have almost the same issue. But I want to tune some video stream params.
First of all I want to set FPS and frequency of k-frames. Now I'm doing this so:

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cvlc v -vvv v4l2:///dev/video0:width=640:height=360:fps=5:keyint=4:chroma=h264 --sout "#standard{access=http,mux=ts,dst=:5000}" --no-sout-audio

But I this that doesn't work because of this string in the output:

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[0x41b03000] v4l2 demux debug: added new video es h264 640x360 [b][0x41b03000] v4l2 demux debug: frame rate: 0.000000[/b]

May be I'm doing something wrong?

[Rémi Denis-Courmont]

"fps" and "keyint" are not currently implemented by the V4L2 input plugin. fps is not a V4L2 "control" anyway, so it would need special support. I don't know about "keyint".

[madrugado]

Hi Rémi,

Is there any frame rate control available in V4L2 input plugin? Or there is some option like use v4l2-ctl to set parameters I need ahead of vlc use?

[Rémi Denis-Courmont]

No, this never was implemented in VLC.