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Improve MTA2 decoding accuracy

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This commit is contained in:
bnnm 2022-04-16 22:18:58 +02:00
parent cfca5c3195
commit 8a3379bd40
1 changed files with 24 additions and 13 deletions
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37
src/coding/mta2_decoder.c
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@ -4,30 +4,37 @@
/* MTA2 decoder based on:
* - MGS Developer Wiki: https://www.mgsdevwiki.com/wiki/index.php/MTA2_(Codec) [codec by daemon1]
* - Solid4 tools: https://github.com/GHzGangster/Drebin
* (PS3 probably uses floats, so this may not be 100% accurate)
* - Partially reverse engineered to fix tables
* - Internal codec name may be "vax2", with Mta2 being the file format.
*
* MTA2 layout:
* - data is divided into N tracks of 0x10 header + 0x90 frame per track channel, forming N streams
* ex: 8ch: track0 4ch + track1 4ch + track0 4ch + track1 4ch ...; or 2ch = 1ch track0 + 1ch track1
* * up to 16 possible tracks, but max seen is 3 (ex. track0=sneaking, track1=action, track2=ambience)
* - each ch frame is divided into 4 headers + 4 vertical groups with nibbles (0x4*4 + 0x20*4)
* ex. group1 is 0x04(4) + 0x14(4) + 0x24(4) + 0x34(4) ... (vertically maybe for paralelism?)
* ex. group1 is 0x04(4) + 0x14(4) + 0x24(4) + 0x34(4) ... (seemingly for vector paralelism)
*
* Due to this vertical layout and multiple hist/indexes, it decodes everything in a block between calls
* but discards unwanted data, instead of trying to skip to the target nibble. Meaning no need to save hist, and
* expects samples_to_do to be block_samples at most (could be simplified, I guess).
*/
/* tweaked XA/PSX coefs << 8 */
/* tblSsw2Vax2K0 / K1 (extended from classic XA's K0/K1 */
static const float VAX2_K0[8] = { 0.0, 0.9375, 1.796875, 1.53125, 1.90625, 1.796875, 1.796875, 0.9375 };
static const float VAX2_K1[8] = { -0.0, -0.0, -0.8125, -0.859375, -0.9375, -0.9375, -0.859375, -0.40625 };
/* tblSsw2Vax2Rng */
static const float VAX2_RANGES[32] = {
1.0, 1.3125, 1.6875, 2.25, 2.9375, 3.8125, 5.0, 6.5625,
8.5625, 11.1875, 14.625, 19.125, 25.0, 32.75, 42.8125, 55.9375,
73.1875, 95.6875, 125.1875, 163.6875, 214.0625, 279.9375, 366.125, 478.8125,
626.125, 818.8125, 1070.8125, 1400.375, 1831.375, 2395.0, 3132.0625, 4096.0
};
/* somewhat equivalent tables K*2^8 (as found elsewhere): */
# if 0
static const int16_t mta2_coefs[8][2] = {
{ 0, 0 },
{ 240, 0 },
{ 460, -208 },
{ 392, -220 },
{ 488, -240 },
{ 460, -240 },
{ 460, -220 },
{ 240, -104 }
{ 0, 0 }, { 240, 0 }, { 460, -208 }, { 392, -220 },
{ 488, -240 }, { 460, -240 }, { 460, -220 }, { 240, -104 }
};
static const int mta2_scales[32] = {
@ -36,6 +43,7 @@ static const int mta2_scales[32] = {
18736, 24503, 32043, 41905, 54802, 71668, 93724, 122568,
160290, 209620, 274133, 358500, 468831, 613119, 801811, 1048576
};
#endif
/* decodes a block for a channel */
void decode_mta2(VGMSTREAMCHANNEL *stream, sample_t *outbuf, int channelspacing, int32_t first_sample, int32_t samples_to_do, int channel, int config) {
@ -120,8 +128,8 @@ void decode_mta2(VGMSTREAMCHANNEL *stream, sample_t *outbuf, int channelspacing,
uint32_t group_header = get_u32be(frame + track_channel*0x90 + group*0x4);
hist2 = (short) ((group_header >> 16) & 0xfff0); /* upper 16b discarding 4b */
hist1 = (short) ((group_header >> 4) & 0xfff0); /* lower 16b discarding 4b */
coefs = (group_header >> 5) & 0x7; /* mid 3b */
scale = group_header & 0x1f; /* lower 5b */
coefs = (group_header >> 5) & 0x07; /* mid 3b */
scale = (group_header >> 0) & 0x1f; /* lower 5b */
/* write header samples (skips the last 2 group nibbles), like Drebin's decoder
* last 2 nibbles and next 2 header hist should match though */
@ -146,8 +154,11 @@ void decode_mta2(VGMSTREAMCHANNEL *stream, sample_t *outbuf, int channelspacing,
sample = col&1 ? /* high nibble first */
get_low_nibble_signed(nibbles) :
get_high_nibble_signed(nibbles);
#if 0
sample = sample * mta2_scales[scale];
sample = (sample + hist1 * mta2_coefs[coefs][0] + hist2 * mta2_coefs[coefs][1] + 128) >> 8;
#endif
sample = (sample * VAX2_RANGES[scale] + hist1 * VAX2_K0[coefs] + hist2 * VAX2_K1[coefs]); /* f32 sample to int */
sample = clamp16(sample);
/* ignore last 2 nibbles (uses first 2 header samples) */