---
libavcodec/ac3enc.c | 22 +++++++++++++++++-----
1 files changed, 17 insertions(+), 5 deletions(-)
diff --git libavcodec/ac3enc.c libavcodec/ac3enc.c
index db1bfe9..ccf0c28 100644
--- libavcodec/ac3enc.c
+++ libavcodec/ac3enc.c
@@ -351,6 +351,21 @@ static void lshift_tab(int16_t *tab, int n, int lshift)
}
}
+/**
+ * Normalize the input samples to use the maximum available precision.
+ * This assumes signed 16-bit input samples. Exponents are reduced by 9 to
+ * match the 24-bit internal precision for MDCT coefficients.
+ *
+ * @return exponent shift
+ */
+static int normalize_samples(AC3EncodeContext *s)
+{
+ int v = 14 - log2_tab(s->windowed_samples, AC3_BLOCK_SIZE*2);
+ v = FFMAX(0, v);
+ lshift_tab(s->windowed_samples, AC3_BLOCK_SIZE*2, v);
+ return v - 9;
+}
+
static void apply_window(int16_t *output, const int16_t *input,
const int16_t *window, int n)
{
@@ -370,7 +385,7 @@ static void apply_window(int16_t *output, const int16_t *input,
static void apply_mdct(AC3EncodeContext *s)
{
- int blk, ch, v;
+ int blk, ch;
for (ch = 0; ch < s->channels; ch++) {
/* fixed mdct to the six sub blocks & exponent computation */
@@ -382,10 +397,7 @@ static void apply_mdct(AC3EncodeContext *s)
AC3_BLOCK_SIZE*2);
/* Normalize the samples to use the maximum available precision */
- v = 14 - log2_tab(s->windowed_samples, AC3_BLOCK_SIZE*2);
- v = FFMAX(0, v);
- s->blocks[blk].exp_shift[ch] = v - 9;
- lshift_tab(s->windowed_samples, AC3_BLOCK_SIZE*2, v);
+ s->blocks[blk].exp_shift[ch] = normalize_samples(s);
/* do the MDCT */
calc_mdct(&s->mdct, s->blocks[blk].mdct_coef[ch], s->windowed_samples);
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