ref: 38ea1ac105f4484f02bba3bfbc790ebe4f18f016
dir: /sys/src/cmd/audio/mp3enc/reservoir.c/
/*
* bit reservoir source file
*
* Copyright (c) 1999 Mark Taylor
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/* $Id: reservoir.c,v 1.14 2001/01/05 15:20:33 aleidinger Exp $ */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <assert.h>
#include "util.h"
#include "reservoir.h"
#ifdef WITH_DMALLOC
#include <dmalloc.h>
#endif
/*
ResvFrameBegin:
Called (repeatedly) at the beginning of a frame. Updates the maximum
size of the reservoir, and checks to make sure main_data_begin
was set properly by the formatter
*/
/*
* Background information:
*
* This is the original text from the ISO standard. Because of
* sooo many bugs and irritations correcting comments are added
* in brackets []. A '^W' means you should remove the last word.
*
* 1) The following rule can be used to calculate the maximum
* number of bits used for one granule [^W frame]:
* At the highest possible bitrate of Layer III (320 kbps
* per stereo signal [^W^W^W], 48 kHz) the frames must be of
* [^W^W^W are designed to have] constant length, i.e.
* one buffer [^W^W the frame] length is:
*
* 320 kbps * 1152/48 kHz = 7680 bit = 960 byte
*
* This value is used as the maximum buffer per channel [^W^W] at
* lower bitrates [than 320 kbps]. At 64 kbps mono or 128 kbps
* stereo the main granule length is 64 kbps * 576/48 kHz = 768 bit
* [per granule and channel] at 48 kHz sampling frequency.
* This means that there is a maximum deviation (short time buffer
* [= reservoir]) of 7680 - 2*2*768 = 4608 bits is allowed at 64 kbps.
* The actual deviation is equal to the number of bytes [with the
* meaning of octets] denoted by the main_data_end offset pointer.
* The actual maximum deviation is (2^9-1)*8 bit = 4088 bits
* [for MPEG-1 and (2^8-1)*8 bit for MPEG-2, both are hard limits].
* ... The xchange of buffer bits between the left and right channel
* is allowed without restrictions [exception: dual channel].
* Because of the [constructed] constraint on the buffer size
* main_data_end is always set to 0 in the case of bit_rate_index==14,
* i.e. data rate 320 kbps per stereo signal [^W^W^W]. In this case
* all data are allocated between adjacent header [^W sync] words
* [, i.e. there is no buffering at all].
*/
int
ResvFrameBegin(lame_global_flags *gfp,III_side_info_t *l3_side, int mean_bits, int frameLength )
{
lame_internal_flags *gfc=gfp->internal_flags;
int fullFrameBits;
int resvLimit;
int maxmp3buf;
/*
* Meaning of the variables:
* resvLimit: (0, 8, ..., 8*255 (MPEG-2), 8*511 (MPEG-1))
* Number of bits can be stored in previous frame(s) due to
* counter size constaints
* maxmp3buf: ( ??? ... 8*1951 (MPEG-1 and 2), 8*2047 (MPEG-2.5))
* Number of bits allowed to encode one frame (you can take 8*511 bit
* from the bit reservoir and at most 8*1440 bit from the current
* frame (320 kbps, 32 kHz), so 8*1951 bit is the largest possible
* value for MPEG-1 and -2)
* fullFrameBits:
*
* mean_bits:
*
* frameLength:
*
* gfc->ResvMax:
*
* gfc->ResvSize:
*
* l3_side->resvDrain_pre:
*
*/
/* main_data_begin has 9 bits in MPEG-1, 8 bits MPEG-2 */
resvLimit = (gfp->version==1) ? 8*511 : 8*255 ;
/* maximum allowed frame size */
maxmp3buf = (gfp->strict_ISO) ? 8*960 : 8*2047;
if ( frameLength > maxmp3buf || gfp->disable_reservoir ) {
gfc->ResvMax = 0;
} else {
gfc->ResvMax = maxmp3buf - frameLength;
if ( gfc->ResvMax > resvLimit )
gfc->ResvMax = resvLimit;
}
fullFrameBits = mean_bits * gfc->mode_gr + Min ( gfc->ResvSize, gfc->ResvMax );
if ( gfp->strict_ISO && fullFrameBits > maxmp3buf )
fullFrameBits = maxmp3buf;
assert ( 0 == gfc->ResvMax % 8 );
assert ( gfc->ResvMax >= 0 );
l3_side->resvDrain_pre = 0;
if ( gfc->pinfo != NULL ) {
gfc->pinfo->mean_bits = mean_bits / 2; /* expected bits per channel per granule [is this also right for mono/stereo, MPEG-1/2 ?] */
gfc->pinfo->resvsize = gfc->ResvSize;
}
return fullFrameBits;
}
/*
ResvMaxBits
returns targ_bits: target number of bits to use for 1 granule
extra_bits: amount extra available from reservoir
Mark Taylor 4/99
*/
void ResvMaxBits(lame_global_flags *gfp, int mean_bits, int *targ_bits, int *extra_bits)
{
lame_internal_flags *gfc=gfp->internal_flags;
int add_bits;
int full_fac;
*targ_bits = mean_bits ;
/* extra bits if the reservoir is almost full */
full_fac=9;
if (gfc->ResvSize > ((gfc->ResvMax * full_fac) / 10)) {
add_bits= gfc->ResvSize-((gfc->ResvMax * full_fac) / 10);
*targ_bits += add_bits;
}else {
add_bits =0 ;
/* build up reservoir. this builds the reservoir a little slower
* than FhG. It could simple be mean_bits/15, but this was rigged
* to always produce 100 (the old value) at 128kbs */
/* *targ_bits -= (int) (mean_bits/15.2);*/
if (!gfp->disable_reservoir)
*targ_bits -= .1*mean_bits;
}
/* amount from the reservoir we are allowed to use. ISO says 6/10 */
*extra_bits =
(gfc->ResvSize < (gfc->ResvMax*6)/10 ? gfc->ResvSize : (gfc->ResvMax*6)/10);
*extra_bits -= add_bits;
if (*extra_bits < 0) *extra_bits=0;
}
/*
ResvAdjust:
Called after a granule's bit allocation. Readjusts the size of
the reservoir to reflect the granule's usage.
*/
void
ResvAdjust(lame_internal_flags *gfc,gr_info *gi, III_side_info_t *l3_side, int mean_bits )
{
gfc->ResvSize += (mean_bits / gfc->channels_out) - gi->part2_3_length;
#if 0
printf("part2_3_length: %i avg=%i incres: %i resvsize=%i\n",gi->part2_3_length,
mean_bits/gfc->channels_out,
mean_bits/gfc->channels_out-gi->part2_3_length,gfc->ResvSize);
#endif
}
/*
ResvFrameEnd:
Called after all granules in a frame have been allocated. Makes sure
that the reservoir size is within limits, possibly by adding stuffing
bits.
*/
void
ResvFrameEnd(lame_internal_flags *gfc, III_side_info_t *l3_side, int mean_bits)
{
int stuffingBits;
int over_bits;
/* just in case mean_bits is odd, this is necessary... */
if ( gfc->channels_out == 2 && (mean_bits & 1) )
gfc->ResvSize += 1;
stuffingBits=0;
l3_side->resvDrain_post = 0;
l3_side->resvDrain_pre = 0;
/* we must be byte aligned */
if ( (over_bits = gfc->ResvSize % 8) != 0 )
stuffingBits += over_bits;
over_bits = (gfc->ResvSize - stuffingBits) - gfc->ResvMax;
if (over_bits > 0) {
assert ( 0 == over_bits % 8 );
assert ( over_bits >= 0 );
stuffingBits += over_bits;
}
#define NEW_DRAINXX
#ifdef NEW_DRAIN
/* drain as many bits as possible into previous frame ancillary data
* In particular, in VBR mode ResvMax may have changed, and we have
* to make sure main_data_begin does not create a reservoir bigger
* than ResvMax mt 4/00*/
{
int mdb_bytes = Min(l3_side->main_data_begin*8,stuffingBits)/8;
l3_side->resvDrain_pre += 8*mdb_bytes;
stuffingBits -= 8*mdb_bytes;
gfc->ResvSize -= 8*mdb_bytes;
l3_side->main_data_begin -= mdb_bytes;
/* drain just enough to be byte aligned. The remaining bits will
* be added to the reservoir, and we will deal with them next frame.
* If the next frame is at a lower bitrate, it may have a larger ResvMax,
* and we will not have to waste these bits! mt 4/00 */
assert ( stuffingBits >= 0 );
l3_side->resvDrain_post += (stuffingBits % 8);
gfc->ResvSize -= stuffingBits % 8;
}
#else
/* drain the rest into this frames ancillary data*/
l3_side->resvDrain_post += stuffingBits;
gfc->ResvSize -= stuffingBits;
#endif
return;
}