On Sunday 20 August 2006 01:38, Bernhard Praschinger wrote:
> Hallo
>
> > I'm new to this list and to mjpeg.
> > I was wondering if there is an easy to to feed an mpeg2
> > video into one or more of the tools and extract jpg's to
> > create a storyboard?
>
> When you decode the mpeg to mjpeg how do you do that ?
I've been trying to use mpeg2decode for that.
All it seems to do however is output to individual files - not stdout.
> When you use ppmtoy4m I think the -n option would be also worth looking.
>
> BTW: Lavrec has the time-lapse mode where it records only very n'th frame.
I'm not recording, I'm just using a test mpeg file at the moment.
> > I looked through the MJPEG Howto, but didn't see anything
> > exactly like that. What I found was 'lavtrans' that can extract
> > all the frames, or a specific one. What I'm thinking is that it'd
> > be nice to grab say every thousandth or ten thousandth frame
> > and put that into a jpg. Perhaps it's simply a matter of
> > calling lavtrans in a loop with different -i settings? If I extract
> > the 100 thousandth frame, does it do this by seeking to that
> > frame instead of reading up to and tossing the first 99999 frames?
>
> lavtrans is very quick. It does not need to decode all the frames
> before. To come to frame 10000. Using lavtrans would be a possible
> solution.
lavtrans doesn't understand the mpeg input file.
And it also looks like I'd need to execute lavtrans in some sort of loop.
What I did finally come up with, in case anyone is intereseted
is to my mind - a hack.
I'm using mpeg2decode to dump all the frames in PPM format
to a temporary directory. Then I determine from those frames
which ones I want for my storyboard (atm - simply count them
all and divide by how many I want and add those to my "list").
And then cat them all into pampick (given my list as an argument),
which pipes to pamsplit. Then, run pnmtojpeg individually on each
of the output files from pamsplit. This is not pretty, a hack like I
said. It uses a tempory directory and duplicates the mpeg file
as individual frames in that directory. Double the disk storage
in effect just to create a storyboard of jpeg's.
What I'd really like is for mpeg2decode to do most of this
given an option. Something like "-n integer Number of
frames to extract" or something similar. Then, instead of
actually outputting all the frames, just output the N key frames
that I asked for. Say, frame 0, 16, 32, 48, 64, etc...
If there was an easy way to determine how many frame were
in the mpeg, I could easily compute what N should be
depending on how many frames I wanted in my storyboard.
The test mpeg I'm using has 201 frames and I've been using
12 jpegs in a storyboard so what I need are frames
0 16 32 48 64 80 96 112 128 144 160 and 176 for this
particular test mpeg.
What'd I'd like to be able to do is be able to give mpeg2decode
an option (n) and have it output the chosen frames to files.
I can live with the PPM output and do the conversion to what
I actually want I guess - but at the moment, it'd be nice if one
of the output types was jpeg's. :)
Alternatively, if mpeg2decode wrote to stdout... I could work
with that as well. This is probably the easier change, but I
do notice that mpeg2decode is kind of chatty - so that would
need to be fixed as well so the stream wouldn't be messed up.
If I get around to making either of these changes to mpeg2decode, I'll
certainly let you all know. If someone else does it first, I'd like
to hear about it...
Or, if someone has some other suggestion, I'd *really* like to
hear that. :)
Bernhard - thank you for your input, it helped me out a bit.
Thanks all!
-Dan
--
Dan A. Dickey
[EMAIL PROTECTED]
SAVVIS
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