[AG-TECH] AccessGrid 3: What information is available
Andrew A Rowley
Andrew.Rowley at manchester.ac.uk
Wed May 25 02:39:53 CDT 2005
Hi,
I am unsure of how much more work Sun is planning to
provide to the JMF. From my experience with
ScreenStreamer, I found the current JMF very easy to use.
As you say, one of the problems is with a lack of codecs.
However, Java does support the use of other native
libraries and so it should be relatively easy to import
any codecs used in vic into JMF with a little work, or to
use libraries such as ffmpeg for MPEG4 support (I think
JMF uses native libraries anyway, but this is all hidden
from the programmer). Alternatively, writing codecs in
pure Java would be very nice - I have written a basic
H.261 encoder which is slow currently due to the small
amount of time I spent on it (the slowness is due to the
fact I wrote a quick and simple DCT algorithm). I expect
most people will be afraid of Java being too slow, but
modern Java VMs can run easily as fast as native
equivalents.
The main thing that is good about the JMF is the way that
it handles the RTP/RTCP for you. This means that the main
body of your proram can stay fairly static once it has
been developed. If you want to add codecs, you just add
an option to your program to use your codec (as I did with
H.261) and it uses this instead of the built in ones.
File handling is similar to reading from a camera, so it
would be very easy to write something that takes an MPEG
and streams that in RTP.
I would recommend JMF as a good starting ground for
developing cross-platform media tools. I will reiterate
that I have already done a lot of work towards this in
ScreenStreamer and anyone who wants to see the code for
this is more than welcome.
Andrew :)
> Hi Andrew,
>
> Is JMF receiving much development as a Java toolkit. We
did some work a
> few years ago on a JMF based video transcoder. It has a
lot of potential
> in that regard because of its architecture. As you say,
you just plug in
> new codecs as they are developed.
>
> What we found was that there was no much capability to
encode to very
> many formats, and therefore we could decode a number of
formats but we
> could only encode back to h261. Not the best for a
transcoder 8-)
>
> I would be interested in hearing what the status is at
the moment. We
> haven't done any JMF work for a while.
>
> Brian
>
>
> Andrew Rowley wrote:
>
> > Hi,
> >
> > The ScreenStreamer code (http://www.memetic-
vre.net/software/ScreenStreamer)
> > at one point in the development cycle had some
features that would allow it
> > to be a vic/rat replacement. This is Java code using
Java Media Framework,
> > so it is already platform independent. If you have
used this, you will
> > notice that the interface already looks a bit like
vic. This has been
> > slimmed down to only support screen sending, but it
would not take much work
> > to add the video sending back in. It also had some
support for audio
> > transmission and reception so this would allow audio
and video from one
> > client.
> >
> >>From what I remember, the main problems were that
> > a) The H.261 encoder is a bit slow as I wrote this
from scratch and have not
> > spent much time on it
> > b) JMF doesn't include the AG audio codec so this
would need implementing.
> > This should not be very hard given that AG audio is
uncompressed as far as I
> > know.
> >
> > JMF already has H.261 video decoding, and Java video
encoding and decoding
> > for better quality than H.261. The framework is quite
nice in that JMF
> > handles most of the RTP things, and you can just plug
in new codecs as they
> > are written.
> >
> > Just a suggestion - if anyone wants the ScreenStreamer
code to look at, let
> > me know and I will arrange access.
> >
> > Andrew :)
> >
> > ============================================
> > Access Grid Support Centre,
> > RSS Group,
> > Manchester Computing,
> > Kilburn Building,
> > University of Manchester,
> > Oxford Road,
> > Manchester,
> > M13 9PL,
> > UK
> > Tel: +44(0)161-275 0685
> > Email: Andrew.Rowley at manchester.ac.uk
> >
> >
> >>-----Original Message-----
> >>From: owner-ag-tech at mcs.anl.gov [mailto:owner-ag-
tech at mcs.anl.gov] On
> >>Behalf Of Steve Smith
> >>Sent: 24 May 2005 09:15
> >>To: Rhys Hawkins
> >>Cc: barz at nchc.org.tw; ag-tech at mcs.anl.gov
> >>Subject: Re: [AG-TECH] AccessGrid 3: What information
is available
> >>
> >>
> >>>Agreed! Parts of VIC/RAT are worth reusing (eg
libcommon) but I think
> >>>its time to get rid of the TCL/TK reliance. I think
there is enough
> >>>people working in the area of video tools for the
AccessGrid to start
> >>>a community development aimed a replacing VIC in the
AG.
> >>
> >>I agree with this in principle, but that will take
some time and while
> >>that effort is taking place we need knock the worst of
the issues out of
> >>current tools (redirecting your efforts to a new
implementation while
> >>ignoring the existing is always disaster, Joel Spolsky
has written about
> >>this extensively).
> >>
> >>In particular I think the following would be major
leaps forward in
> >>usability:
> >>
> >> * Being able to change the venue in Vic and
Rat without
> >> restarting them
> >> * Multiple video inputs to Vic (which would
remove the necessity
> >> of multi-machine nodes)
> >>
> >>Cheers,
> >>Steve
> >>
> >>
> >>
> >
> >
>
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