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From: kabir muhammad on 28 Jul 2010 04:49
i want to compress the iframe only for this i want to separate the i frames so plz send me code for this
From: Steven_Lord on 28 Jul 2010 09:49


"kabir muhammad" <kabirnawab(a)yahoo.com> wrote in message
news:i2oqua$2fl$1(a)fred.mathworks.com...
> i want to compress the iframe only for this i want to separate the i
> frames so plz send me code for this

You may not like the answer Walter gave you the previous time you asked
this, but I don't think the answer's going to change just because you asked
again.

http://www.mathworks.com/matlabcentral/newsreader/view_thread/287661#765249

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ
To contact Technical Support use the Contact Us link on
http://www.mathworks.com

From: Walter Roberson on 28 Jul 2010 10:34
kabir muhammad wrote:
> i want to compress the iframe only for this i want to separate the i
> frames so plz send me code for this

You haven't taken my word for it that this cannot be done, so here is
reference material:

http://en.wikipedia.org/wiki/Video_compression_picture_types#Intra_coded_frames_.28or_slices_or_I.E2.80.91frames_or_Key_frames.29

Intra coded frames (or slices or I‑frames or Key frames)

* Pictures are coded without reference to any pictures except
themselves.
* May be generated by an encoder to create a random access point
(to allow a decoder to start decoding properly from scratch at that
picture location).
* May also be generated when differentiating image details prohibit
generation of effective P or B frames.
* Typically require more bits to encode than other picture types.

Often, I‑frames are used for random access and are used as references
for the decoding of other pictures. Intra refresh periods of a
half-second are common on such applications as digital television
broadcast and DVD storage. Longer refresh periods may be used in some
environments. For example, in videoconferencing systems it is common to
send I frames very infrequently.



The clear implication of the above is that I-frames may be coded
whenever the encoder likes, possibly depending on the purpose the stream
is being put to rather than upon the content of the stream. Matters such
as how often to code a random access point are administrative rather
than technical.


Look more closely at the output of mmreader. Notice that the outputs are
colormap and image frames, and the outputs do NOT include any indication
of what kind of encoding was used for each frame. As I indicated before,
once a frame is fully decoded there is no way to tell what it was. For
example you might be transcoding a video-conference (I-frame about every
30 seconds) into a DVD (I-frame about every 1/2 second).


You should stop worrying about detecting whether a particular frame is
an I-frame (because you can't do that from the decoded stream), and
should just assume that *every* full frame you have been given is an
I-frame and start your compression algorithm from that assumption.
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