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adpcm_ima & adpcm_yamaha: improved quantization

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Originally committed as revision 5449 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Loren Merritt 2006-06-03 04:38:11 +00:00
parent be9701279d
commit 7e5370516b
1 changed files with 11 additions and 53 deletions
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64
libavcodec/adpcm.c
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@ -203,49 +203,11 @@ static int adpcm_encode_close(AVCodecContext *avctx)
static inline unsigned char adpcm_ima_compress_sample(ADPCMChannelStatus *c, short sample) static inline unsigned char adpcm_ima_compress_sample(ADPCMChannelStatus *c, short sample)
{ {
int step_index; int delta = sample - c->prev_sample;
unsigned char nibble; int nibble = FFMIN(7, abs(delta)*4/step_table[c->step_index]) + (delta<0)*8;
c->prev_sample = c->prev_sample + ((step_table[c->step_index] * yamaha_difflookup[nibble]) / 8);
int sign = 0; /* sign bit of the nibble (MSB) */
int delta, predicted_delta;
delta = sample - c->prev_sample;
if (delta < 0) {
sign = 1;
delta = -delta;
}
step_index = c->step_index;
/* nibble = 4 * delta / step_table[step_index]; */
nibble = (delta << 2) / step_table[step_index];
if (nibble > 7)
nibble = 7;
step_index += index_table[nibble];
if (step_index < 0)
step_index = 0;
if (step_index > 88)
step_index = 88;
/* what the decoder will find */
predicted_delta = ((step_table[step_index] * nibble) / 4) + (step_table[step_index] / 8);
if (sign)
c->prev_sample -= predicted_delta;
else
c->prev_sample += predicted_delta;
CLAMP_TO_SHORT(c->prev_sample); CLAMP_TO_SHORT(c->prev_sample);
c->step_index = clip(c->step_index + index_table[nibble], 0, 88);
nibble += sign << 3; /* sign * 8 */
/* save back */
c->step_index = step_index;
return nibble; return nibble;
} }
@ -276,27 +238,23 @@ static inline unsigned char adpcm_ms_compress_sample(ADPCMChannelStatus *c, shor
static inline unsigned char adpcm_yamaha_compress_sample(ADPCMChannelStatus *c, short sample) static inline unsigned char adpcm_yamaha_compress_sample(ADPCMChannelStatus *c, short sample)
{ {
int i1 = 0, j1; int nibble, delta;
if(!c->step) { if(!c->step) {
c->predictor = 0; c->predictor = 0;
c->step = 127; c->step = 127;
} }
j1 = sample - c->predictor;
j1 = (j1 * 8) / c->step; delta = sample - c->predictor;
i1 = abs(j1) / 2;
if (i1 > 7)
i1 = 7;
if (j1 < 0)
i1 += 8;
c->predictor = c->predictor + ((c->step * yamaha_difflookup[i1]) / 8); nibble = FFMIN(7, abs(delta)*4/c->step) + (delta<0)*8;
c->predictor = c->predictor + ((c->step * yamaha_difflookup[nibble]) / 8);
CLAMP_TO_SHORT(c->predictor); CLAMP_TO_SHORT(c->predictor);
c->step = (c->step * yamaha_indexscale[i1]) >> 8; c->step = (c->step * yamaha_indexscale[nibble]) >> 8;
c->step = clip(c->step, 127, 24567); c->step = clip(c->step, 127, 24567);
return i1; return nibble;
} }
static int adpcm_encode_frame(AVCodecContext *avctx, static int adpcm_encode_frame(AVCodecContext *avctx,