[M4IF Technotes] MPEG4 subsampling

[Peter Haighton]

Jayank,
Yes, you would need to fix the modulo time base but you would not need to
skip the vops, you would merely need to change the time in the
modulo_time_base (which most likely would be the same anyway since there
is more than 1 key frame per second in the original source), and change
the vop time increment. You may also need to change the fixed_vop_rate.
However these issues are not as tricky as making sure the rate control is
taken care of so I did not include it in my previous email.
Peter
-----Original Message-----
From: Jayank Bhalod [mailto:jayank   vidiator.com]
Sent: Tuesday, January 21, 2024 3:12 PM
To: Peter Haighton; Wouter Favoreel; Renaud Cazoulat
Cc: technotes   lists.m4if.org
Subject: RE: [M4IF Technotes] MPEG4 subsampling
But there is still a one problem with just extracting out the I-frames.
Let assume that by appropriate Rate Control one can regulate the VBV
buffer but still the modulo time base or frame rate would still have
problems. I guess if we replace all the frames which we want to skip by
VOP Coded=0, this would help. As decoder will keep the frame and the frame
rate will ramain same.
-Jayank
-----Original Message-----
From: Peter Haighton [mailto:Peter.Haighton   m4if.org]
Sent: Tuesday, January 21, 2024 10:12 AM
To: Wouter Favoreel; 'Renaud Cazoulat'
Cc: technotes   lists.m4if.org
Subject: RE: [M4IF Technotes] MPEG4 subsampling
Wouter
Extracting the MPEG-4 Intra frames is easy in theory and the video will
look good for low frame applications as long as the I frames are
reasonably equally spaced. In the application that I suspect you are using
it for, this should work well.  However, since I frames can be quite
large, you may also need to rate control the frames in order to bring the
video down to the network bitrates you are looking for. In a previous life
I had done exactly this and the results worked quite well.
Unfortuately, I am not aware of any software available (for purchase)
today that will do what you are looking for.
Peter
-----Original Message-----
From: technotes-admin   lists.m4if.org
[mailto:technotes-admin   lists.m4if.org]On Behalf Of Wouter Favoreel
Sent: Tuesday, January 21, 2024 10:36 AM
To: 'Renaud Cazoulat'; Wouter Favoreel
Cc: 'technotes   lists.m4if.org'
Subject: RE: [M4IF Technotes] MPEG4 subsampling
Hi Renaud,
Thanks for your quick response.
You are of course right with the 7.5 I frames but 7 or even 5 is ok as
well.
Our point is that we just want a low bandwith stream (not necessarily
MPEG4)
from a high bandwidth MPEG4 stream.
Any idea what a sequence of only I-frames looks like?
Can they be extracted (easily) an MPEG4 stream?
Regards,
Wouter
-----Original Message-----
From: Renaud Cazoulat [mailto:renaud   envivio.com]
Sent: dinsdag 21 januari 2003 16:25
To: Wouter Favoreel
Cc: 'technotes   lists.m4if.org'
Subject: Re: [M4IF Technotes] MPEG4 subsampling
Hi
I guess that the I frame interval is an important variable to take in
account
;-)
You example will work only if the high badwidth video has an Iframe
interval
of
7.5
This value is not yet adopted world wide.
Furthermore, by taking only the I frames you will loose the P (and maybe
B)
frames benefit.
I would say that the best solution is to decode/re-encode.
renaud
Wouter Favoreel wrote:
> Dear,
>
> Is there anyone who knows how to extract a low bandwith compressed video
> stream (e.g. CIF @ 4 fps @ 0.4 Mbps) from a higher bandwith elementary
MPEG4
> stream (CIF @ 30 fps @ 2Mbps) ?
>
> We thought of only taking the intraframes ? Maybe there is another
solution?
>
> Thanks for your time,
>
> Wouter Favoreel
>
> Tel. + 32 56 36 17 25
> Fax. + 32 56 36 21 96
>
> _______________________________________________
> Technotes mailing list
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