Re: Windows Webcam access.

[Corion]

In a (soon to be released version of) App::VideoMixer, I use ffmpeg.exe to capture the video and output as a raw bytestream to stdout. The essential command line is:

    my $pixel_format = 'rgb24';
    my $file = 0; # device number 0, or .avi file, for reproducible te
+sting
    my ($pid,$stream) = $self->spawn(sprintf qq{%s -f vfwcap -r 30 -i 
+%s -f rawvideo -pix_fmt %s - |},
        $self->ffmpeg, $file, $pixel_format
    );

It works like a charm with ffmpeg v0.5 and saves me the hassle of downloading and compiling a lot of hard to compile libraries and their prerequisites.

[Steve_BZ]

In order to get the slider functions working I am planning to use something like:

ffmpeg -f vfwcap -r 25 -i 0  -f image2 temp_photos\foo_-%03d.jpeg

In order to give me a directory of "frames" without any exclusive lock. This works, although I'm not sure what the highest number is, or what it'll do to my disc fragmentation!

Then I can just do a while loop through them, and they'll look like a video. On exit, I'll do the opposite and recombine them into a video.

However, it's not the most elegant, if I could do it nearer to your method I would, however I do need to write something to a file, because wxMediaCtrl needs a filename or URL

Regards

[Corion]

I'm not sure where a slider control can come in helpful, because for me, time is still linear. I'd be very interested if you could show me how to control/adjust the flow of time through a slider, especially if it works in both directions :).

But if you want to farm out start/stop/rewind of a movie to another control (which is sensible), my approach of reading single frames won't work out unless the control has a way for you to feed it single frames. Maybe you can hand the control a filehandle instead of an URL or a filename, but (pipe) filehandles have the disadvantage of not being seekable...

[Steve_BZ]

Hi Corion,

I've had a look a VideoMixer, thanks for this. I'm using wxMediaCtrl to output. I've tried streaming FFMPEG to a file (which works) and then opening with wxMediaCtrl, (which doesn't, because the file is opened with an exclusive lock by FFMPEG). I need wxMediaCtrl to be able to work a bit like Youtube with a sliderbar to rewind and play parts of the video, I also want to take snaps and clips and stuff. This is all working if I play an .avi file. However, I've only made it work for a live source with a streaming Server like BraodCam, which degrades the quality as it assumes inet delivery.

Your plan uses standard output and FFMPEG, which seems like a good idea. I think I can make it work with FFMPEG, but what command do you use to stop it?

I've looked through VideoMixer, but I can't see where you stop the streaming process. I'm not familiar with GL, so maybe I just missed it.

Thanks for your help.

regards

[Corion]

I simply kill the process upon exit. That's not the most grateful thing but it works:

package App::VideoMixer::External::FFmpeg;
use strict;

use vars qw($VERSION);
$VERSION = '0.02';

use parent 'Class::Accessor';
__PACKAGE__->mk_accessors(qw(width height depth pid stream texture_id 
+file pixel_format ffmpeg));

sub spawn {
    my ($self,$cmd) = @_;
    my $pid = open my $stream, $cmd
        or die "Couldn't spawn '$cmd': $!/$?";
    binmode $stream;
    return ($pid,$stream)
};

sub DESTROY {
    if (my $pid = $_[0]->pid) {
        kill 9, $pid
    };
};

This will kill the external process once the object gets destroyed. You can read the data from $stream and you have to set $self->pid to the returned $pid (and looking at this code, I'm not sure why ->spawn does it that way instead of setting $pid instead - I guess it's because I turned a subroutine into an object later).

As a side note, App::VideoMixer v0.02 is in a sad state, as even the distribution is incomplete, so I'll have to release a fixed version soonish.

[Steve_BZ]

Hi Corion,

It's very conventional of you you rely on time being linear: how else do you explain coincidence?

However, I'm going to have a look at your code, maybe if I save each frame in a file AFTER it's displayed then I can use my video bar on it.

I'll let you know

Regards