Howdy,
taking a look and adding debug output to VBR_iteration_loop in quantize.c, I
have a couple of questions. I probably don't have a complete understanding
of what I am looking at, but here goes anyway.
First, It appears that it starts at the max bitrate and work our ways down
to the min bitrate, calling outer_loop each time and comparing the noise
values to see what rate is the best. I put in some output to print the
variable 'better' for each loop and observed that, for most of the cases,
once better was 0 (false), it usually stayed false for the remaining
attempts. I put a break into the better test,
if (better)
{
save_bits[gr][ch] = this_bits;
this_bits -= dbits;
}
else
{
this_bits += dbits;
break;
}
to exit the loop. As I expected, I observed a slight speed increase, but
also a slight rasing of the average bitrate. In my test 167kbps became
172kbps. Comments?
Second, since it checks for noise values each time, in VBR_compare, is there
someway that VBR quality can be used to come up with an acceptable max noise
value and once achieved the checking quits. The loop can start at the min
bitrate, check noise, and if not ok proceed up to the max_bitrate. This way
the program always does at least one time consuming outer_loop, but only
does more work if quality is not acceptable. In other words, optimize by
trying to do as little work as possible.
I would also like to see a max_bitrate command line option for more complete
encoding control. For my ears, and the jazz I encode, 160kbps sounds real
perty. There are some passages, however, that obviously benifit from
192kbps, but I can't hear any difference at even higher bitrates. I grunged
the code in order to encode my music at 160 - 192 VBR, most songs averaging
176kbps. I kept the vbr quality at 5, not sure how this effects the
process. Locking the encoder down to 2 bitrates does speed the encoding
process, and if the above observations are correct, I can see how it could
be made even faster.
thanks.
d:-)
Mark Stephens ([EMAIL PROTECTED]) - Fairfield, OH Zone 5
----
http://home.one.net/users/markws - Our Backyard Forest
http://gilmore.pond.org - Gilmore Ponds Conservancy
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