Hi,
On Sun, Apr 17, 2011 at 11:39 AM, Justin Ruggles
<[email protected]> wrote:
[..]
> + /* calculate energy in each band in coupling channel and each fbw
> channel */
> + bnd = 0;
> + i = s->start_freq[CPL_CH];
> + while (i < s->cpl_end_freq) {
> + int band_size = s->cpl_band_sizes[bnd];
> + for (ch = CPL_CH; ch <= s->fbw_channels; ch++) {
> + for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
> + AC3Block *block = &s->blocks[blk];
> + if (!block->cpl_in_use || (ch > CPL_CH &&
> !block->channel_in_cpl[ch]))
> + continue;
> + for (j = 0; j < band_size; j++) {
> + float v = block->mdct_coef[ch][i+j];
> + energy[blk][ch][bnd] += v * v;
This looks somewhat SIMD'able. (Don't bother if an existing simd
function doesn't already exist, but sum of squares seems common enough
to exist...)
> + coord = 0.125f;
> + if (energy_cpl > 0)
> + coord = sqrtf(energy_ch / energy_cpl) / 8.0f;
coord *= sqrtf(energy_ch / energy_cpl);
> @@ -1129,7 +1489,21 @@ static int compute_bit_allocation(AC3EncodeContext *s)
> ret = cbr_bit_allocation(s);
> while (ret) {
> - /* fallback 1: downgrade exponents */
> + /* fallback 1: disable channel coupling */
> + if (s->cpl_on) {
> + s->cpl_on = 0;
> + apply_mdct(s);
> + compute_coupling_strategy(s);
> + compute_rematrixing_strategy(s);
> + scale_coefficients(s);
> + compute_rematrixing_strategy(s);
> + apply_rematrixing(s);
> + process_exponents(s);
> + ret = compute_bit_allocation(s);
> + continue;
> + }
> +
> + /* fallback 2: downgrade exponents */
> if (!downgrade_exponents(s)) {
> extract_exponents(s);
> encode_exponents(s);
So if there's no bits left, first thing you do is to disable channel
coupling. Does that always provide less quality loss per bits saved
than changing exponents? Since you now have multiple things to try,
you could maybe try both and calculate which provides best "bits saved
per quality loss" scenarios.
Ronald
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