How to recompress MPEG-4?

How to recompress MPEG-4?

Post by pancrazio. » Fri, 17 Dec 2004 20:03:42

Hello to all,
I have to build a gateway that receives an MPEG-4 (simple profile)
stream at datarate M and, in realtime, recompress it to obtain an
MPEG-4 stream at a lower datarate O < M.
I have written all software to receive and transmit using RTP and
Transport Stream (mux/demix) but I don't know how to recompress without
passing through the decode-encode chain that is very expensive.

Do you know if there is a way to process an MPEG-4 stream to lower the
resolution and bitrate?

Thank you very much,

How to recompress MPEG-4?

Post by Phil Frisb » Sat, 18 Dec 2004 02:06:19

There is no other way besides decoding and encoding at a lower resolution.

Or, you could simply drop some full frames and let the decoder handle the loss...

Phil Frisbie, Jr.
Hawk Software


How to recompress MPEG-4?

Post by Nils » Sun, 19 Dec 2004 09:41:43

Decode the huffmann compression of macroblocks, and recompress them with a
different (coarser) quantisation matrix.

There's no need to do the full jpeg IDCT/DCT step (which is the most

However, let's hope your original stream has enough I-frames, because this
approach may suffer increasing quality loss over a couple of frames.