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Fix corrupt when repeatidly playing very low bitrate WMA files.

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The LSP feature in WMA requires that the noise table values be
doubled verses when it is not used.  Unfortunately, the previous
code would double the same values every time a LSP file was
decoded without first resetting them to their original values.
Change the code to check if the values are already doubled, and
then double/halve them as needed.  This is still a bit ugly,
in the future consider using the built in rockbox dither instead
of a lookup table.

Fixes playback when skipping back and forth between low and high
bitrate WMA.

Change-Id: I4c393092e4a789bc8f98d74274fe207400b9550e
Reviewed-on: http://gerrit.rockbox.org/226
Reviewed-by: Michael Giacomelli <giac2000@hotmail.com>
Tested-by: Michael Giacomelli <giac2000@hotmail.com>
This commit is contained in:
Michael Giacomelli 2012-04-30 23:28:57 -04:00
parent f5d9a45e3f
commit 87d3dde15a
2 changed files with 17 additions and 6 deletions
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3
lib/rbcodec/codecs/libwma/wmadata.h Normal file → Executable file
View file

@ -1578,7 +1578,8 @@ const fixed64 lsp_pow_e_table[] ICONST_ATTR_WMA_XL_IRAM =
0x0LL
};
/* table of exp noise values multiplied by 16 in order to reduce rounding error */
/* table of exp noise values multiplied by 16 in order to reduce rounding error,
* note that that first value (0x5) is used as a magic number in the init code*/
fixed32 noisetable_exp[] =
{
0x5, 0xfffffa2e, 0xc2c, 0xb47, 0xffffaebe, 0xfffffa63, 0xfffff7ff, 0x16bd,

20
lib/rbcodec/codecs/libwma/wmadeci.c Normal file → Executable file
View file

@ -487,23 +487,33 @@ int wma_decode_init(WMADecodeContext* s, asf_waveformatex_t *wfx)
s->reset_block_lengths = 1;
if (s->use_noise_coding)
if (s->use_noise_coding) /* init the noise generator */
{
/* init the noise generator */
/* LSP values are simply 2x the EXP values */
if (s->use_exp_vlc)
{
s->noise_mult = 0x51f;
/*unlikely, but we may have previoiusly used this table for LSP,
so halve the values if needed*/
if(noisetable_exp[0] == 0x10) {
for (i=0;i<NOISE_TAB_SIZE;++i)
noisetable_exp[i] >>= 1;
}
s->noise_table = noisetable_exp;
}
else
{
s->noise_mult = 0xa3d;
/* LSP values are simply 2x the EXP values */
for (i=0;i<NOISE_TAB_SIZE;++i)
noisetable_exp[i] = noisetable_exp[i]<< 1;
/*check that we haven't already doubled this table*/
if(noisetable_exp[0] == 0x5) {
for (i=0;i<NOISE_TAB_SIZE;++i)
noisetable_exp[i] <<= 1;
}
s->noise_table = noisetable_exp;
}
#if 0
/*TODO: Rockbox has a dither function. Consider using it for noise coding*/
/* We use a lookup table computered in advance, so no need to do this*/
{
unsigned int seed;