Re: [Ffmpeg-user] performance of dc1394_vloopback ->v4l feeding ffmpeg

On Thu, Oct 14, 2004 at 05:25:49PM -0700, john Galloway wrote:
>
> On Oct 13, 2004, at 6:09 PM, Roman Shaposhnick wrote:
> > So, since I don't have an access to any "IIDC-based" cameras
> > (donation anyone :-) ?) I need someone motivated enough to
> > test this for me. If there's somebody interested -- let me
> > know. The idea is to be able to do:
> >
> > $ ./ffmpeg -video1394 test.mpeg
> >
> I've been doing some tests using dc1394_vloopback and the v4l
> vloopback.ko module. Comparing my Dell 2.4Ghz P4 with my
> mini-itx 1Ghz VIA C3, cpu percentages are
> DELL miniitx
> dc1394_vloopback 22 54
> ffmpeg 7 27
> ffplay 4 17
>
> So while ffmpeg and ffplay consume 4x the cpu on the tiny box
> and dc1394_vloopback is only 2.5x, I need both of the ff's, and
> they are still low compared to 1394 4vl loopback which maybe
> can be eliminated.
>
> This is running entirely locally with the camera in 320x240 mode
> dc1394_vloopback --vloopback=/dev/video0 --width=320 --height=240
> ffmpeg -an -s 320x240 -vd /dev/video1 -intra -vcodec h263p -f h263 |
> ffplay -
>
> All the binaries were built on the Dell so its also possible that gcc
> could produce better code for the C3 if the C3 was the target, I don't
> know that one way or the other.
>
> I'm using h263 as it just seemed to produce the best results with
> lower overhead than mpeg (when transmitting this over a wireless link
> which is the goal). Not sure -intra effects h263 either, but was left
> from mpeg testing where it definitely helps with real time.
>
> The camera produces (depending on settings) YUV422 or YUV411
> (with 640x480 or 320x240 and fps options), which dc1394_vloopback
> translates into YUV420p as that is what is negotiated with
> v4l, and I think it does this first by translating into RGB.
> So if ffmpeg can directly understand YUV422 and/or YUV411 (which
> seems likely) then a lot of crunching might be eliminated with
> lower memory bandwidth used (also a big factor).
>
> Given the example of dc1394_vloopback it "should" not be tooooo
> hard (but having not looked into the innards of ffmpeg...).
> Anyway I'll be looking into it over the next few days.

  Right. That's exactly how -dv1394 works in ffmpeg -- zerro copying.
  And it sure frees quite a few CPU cycles. Plus there's no '|' overhead
  too.

  Let's continue to work offline on hacking up a dc1394 capturing module.

Thanks,
Roman.

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Received on Sun Oct 17 03:49:17 2004