[Mp4-tech] JM8.6 H.264 rate control for TMN H.263 codec

[Gary Sullivan]

Sandip et al,
My recollection is that if we refer to the QP for AVC as QP4 and refer to the QP for H.263 as QP3, the relationship (when using "flat 16" quantization scaling parameters) is approximately:  QP3 = 2^((QP4-12)/6, in terms of the approximate fidelity associated with the QP values.  I think it may have been Gisle Bjontegaard who proposed that basic relationship (although the subtraction of 12 was something we included later).
That may be off by a constant scale factor.
Remember that QP3 is not the quantization step size -- it is half of the basic quantization step size.
Remember also that the norm of the inverse transform needs to be taken into account in such calculations.  H.263 had a unity-norm IDCT, whereas AVC has something else.
Another fine point is the quantization of chroma -- it doesn't always use the same step size as luma does.
Best Regards,
Gary Sullivan
________________________________
From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Sandip Ray
Sent: Thursday, February 21, 2024 10:09 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] JM8.6 H.264 rate control for TMN H.263 codec
Hi,
I want to add a generic rate control algorithm in H.263 TMN encoder because the available rate control algorithm is not good enough to track bitrate efficiently. I earlier worked on JM8.6 rate control algorithm. I feel it is a generic least mean square based rate control algorithm. Please correct me if I am wrong.
I understand that quantization parameter(QP) has range 0 to 51 in H.264 whereas it is 1 to 31 in H.263. The relation between QP and generated bits per frame are not same in both codecs.  H.263 quantizer uses following algorithm which is different from H.264 quantizer.
if (Mode == MODE_INTRA || Mode == MODE_INTRA_Q) { /* Intra */
qcoeff[0] = mmax(1,mmin(254,coeff[0]/8));
for (i = 1; i < 64; i++) {
level = (abs(coeff[i])) / (2*QP);
qcoeff[i] = mmin(127,mmax(-127,sign(coeff[i]) * level));
}
}
else { /* non Intra */
for (i = 0; i < 64; i++) {
level = (abs(coeff[i])-QP/2) / (2*QP);
qcoeff[i] = mmin(127,mmax(-127,sign(coeff[i]) * level));
}
}
In this scenario, Can I use H.264 rate control algorithm in TMN H.263 encoder ?
I will be grateful for any kind of help or pointers in this regard.
Thanks and Regards,
Sandip
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