[vlc] Re: CPU utilization, colors and streaming

[Alexander Isacson]

Hello again

I wrote a similar mail to the one below to Gerard Knorr the author of the
bttv driver and V4L api. This is what he replied. For you information I
have not gotten it to work properly yet.

--------------------------------------------------------------------------
> In order to remedy the colour problem I followed the suggestions from the
> VLC-mailing list to install xawtv and set up the card. After running
> "streamer -d -o pic.jpeg -c /dev/video1" I ran vlc again. Now the colours
> are correct and CPU utilization is down to 40-50% for the big stream!

Sounds like vlc does a incomplete device initialization.

But might also be a issue with the v4l1 compatibility in case you are
using the v4l2 driver and vlc the v4l1 API.

> A significant improvement! The problem now is that I cannot have both
> streams read from the same device, /dev/video1, at the same time.

You can't do that.

> * How do I change the v4l output format? Can I use v4l-conf?

The application using the device must do that.

  Gerd
-------------------------------------------------------------------------

> Hi all.
>
> I'm using VLC to remote control a small robot I’ve been building. The
> situation looks as follows:
>
> I have bought a Spectra 8 card (http://www.ituner.com/spectra.htm) capable
> of capturing 4 simultaneous streams. I'm using three of those on my robot.
> Two of them are fixed B/W cameras and the last one is a colour
> pan-tilt-zoom camera. I'm sending these streams over WLAN to my computer
> using these two commands:
>
> vlc -vvvvv -I rc v4l:/dev/video0:norm=pal:size=400x300
> v4l:/dev/video1:norm=pal:size=400x300
> v4l:/dev/video2:norm=pal:size=400x300 --sout
> '#transcode{vcodec=mp4v,vb2000}:std{access=udp,mux=ts,url=operator:1234}'
>
> vlc -vvvvv -I rc v4l:/dev/video0:norm=pal:size=200x150
> v4l:/dev/video1:norm=pal:size=200x150
> v4l:/dev/video2:norm=pal:size=200x150 --sout
> '#transcode{vcodec=mp4v,vb2000}:std{access=udp,mux=ts,url=operator:1235}'
>
> It all works and I can pick up the two streams on my computer. The problem
> is that the colors are not captured correctly. As described on in my email
> to this list on Nov 7 red looks blue and blue looks red. Except for that
> everything works and the utilization is about 70-75% to encode and stream
> the 400x300 stream and about 20-25% to encode and stream the 200x150
> stream.
> It is possible to have both streams read from either /dev/videoX at the
> same time and I get identical images on the computer. Here are some
> interesting lines in the vlc output:
>
> [00000143] v4l input debug: v4l device uses frame size: 360000
> [00000143] v4l input debug: v4l device uses chroma: RV24
> [00000143] v4l input debug: added new video es RV24 400x300
> [00000144] packetizer_copy decoder debug: Running copy packetizer
> (fcc=RV24)
> [00000146] stream_out_transcode private debug: creating video transcoding
> from fcc=`RV24' to fcc=`mp4v'
> [00000143] main input debug: 3067 loops consuming user: 392, system: 101
> [00000143] main input debug: ES 0x1, stream 0x1, fourcc `RV24', selected
> [OK:0/ERR:0]
> [00000144] main decoder debug: killing decoder for 0x1, fourcc `RV24', 10
> PES in FIFO
>
> In order to remedy the colour problem I followed the suggestions in the
> reply to my last mail and installed xawtv. After running "streamer -d -o
> pic.jpeg -c /dev/video1" I ran vlc again. Now the colours are correct and
> CPU utilization is down to 40-50% for the big stream! A significant
> improvement! The problem now is that I cannot have both streams read from
> the same device, /dev/video1 at the same time. On one stream it seems that
> only every other line is updated a few times a second (really choppy) and
> on the other stream the picture is all dark green. Here are the same lines
> from the vlc output.
>
> [00000143] v4l input debug: v4l device uses frame size: 180000
> [00000143] v4l input debug: v4l device uses chroma: I420
> [00000143] v4l input debug: added new video es I420 400x300
> [00000144] packetizer_copy decoder debug: Running copy packetizer
> (fcc=I420)
> [00000146] stream_out_transcode private debug: creating video transcoding
> from fcc=`I420' to fcc=`mp4v'
> [00000143] main input debug: 1197 loops consuming user: 329, system: 120
> [00000143] main input debug: ES 0x1, stream 0x1, fourcc `I420', selected
> [OK:0/ERR:0]
> [00000144] main decoder debug: killing decoder for 0x1, fourcc `I420', 11
> PES in FIFO
>
> I'v read about the video formats in v4l(2) and looked at the documentation
> for the bttv driver. How do I change the v4l output format? Can it be done
> from within vlc? Can I use v4l-conf? I would like to try every output
> format to see which one works and how much CPU vlc uses to encode it. Once
> I've ran "streamer" I can't get the old colour format back without
> removing the bttv module for the kernel and inserting it again.
>
> The complete output from dmesg after inserting bttv, the output from vlc
> before and after running "streamer" and the output from streamer are
> available here: http://isacson.dyndns.info/media/v4l-debug/
>
> If any other information is needed to resolve this, I'll be more than
> happy to try an provide it.
>
> Thanks in advance!
>
> Regards
> /Alexander Isacson
>
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