[Mp4-tech] Mpeg4 AAC + why exp-=4 (for short windows) else exp-=7
Shreya Pathak
shreya_pathak rediffmail.com
Wed Aug 25 13:02:29 EDT 2004
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Hi,
In Mpeg4 AAC publicly available source code in file specrec.c and
in function apply_scalefactors()
#ifdef FIXED_POINT
exp -= 25;
/* IMDCT pre-scaling */
if (hDecoder->object_type == LD)
{
exp -= 6 /*9*/;
} else {
if (ics->window_sequence == EIGHT_SHORT_SEQUENCE)
exp -= 4 /*7*/;
else
exp -= 7 /*10*/;
}
#endif
I got exp-=25, but I didn't get why this
if (ics->window_sequence == EIGHT_SHORT_SEQUENCE)
exp -= 4 /*7*/;
else
exp -= 7 /*10*/;
is done.
Does any one have any idea on this ?
Please reply asap.
Thanks and Regards
Shreya
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