[FFmpeg-devel] [PATCH] ALAC Encoder
Michael Niedermayer
michaelni
Mon Aug 18 22:38:32 CEST 2008
On Tue, Aug 19, 2008 at 01:09:07AM +0530, Jai Menon wrote:
> Hi,
>
> On Monday 18 Aug 2008 3:46:23 am Michael Niedermayer wrote:
[...]
> > > +
> > > + sign_modifier = 0;
> > > + if(x > 0xFFFF)
> > > + history = 0xFFFF;
> > > +
> > > + if((history < 128) && (i < s->avctx->frame_size)) {
> > > + unsigned int block_size = 0;
> > > +
> > >
> > > + sign_modifier = 1;
> >
> > unused
> >
>
> It is very much used actually. After we have coded a block of zeros, the next
> scalar is non_zero and this sign modifier is applied to that.
no, not this :)
see:
> + sign_modifier = 1;
^^^^^^^^^^^^^
> + k = 7 - av_log2(history) + ((history + 16) >> 6);
> +
> + while((*samples == 0) && (i < s->avctx->frame_size)) {
> + samples++;
> + i++;
> + block_size++;
> + }
> + encode_scalar(s, block_size, k, 16);
> +
> + sign_modifier = (block_size <= 0xFFFF);
^^^^^^^^^^^^^
[...]
> Index: libavcodec/alacenc.c
> ===================================================================
> --- libavcodec/alacenc.c (revision 14824)
> +++ libavcodec/alacenc.c (working copy)
> @@ -38,6 +38,11 @@
> #define ALAC_MAX_LPC_PRECISION 9
> #define ALAC_MAX_LPC_SHIFT 9
>
> +#define ALAC_CHMODE_LEFT_RIGHT 0
> +#define ALAC_CHMODE_LEFT_SIDE 1
> +#define ALAC_CHMODE_RIGHT_SIDE 2
> +#define ALAC_CHMODE_MID_SIDE 3
> +
> typedef struct RiceContext {
> int history_mult;
> int initial_history;
> @@ -53,9 +58,12 @@
>
> typedef struct AlacEncodeContext {
> int compression_level;
> + int min_prediction_order;
> + int max_prediction_order;
> int max_coded_frame_size;
> int write_sample_size;
> int32_t sample_buf[MAX_CHANNELS][DEFAULT_FRAME_SIZE];
> + int32_t predictor_buf[DEFAULT_FRAME_SIZE];
> int interlacing_shift;
> int interlacing_leftweight;
> PutBitContext pbctx;
> @@ -116,6 +124,20 @@
> put_bits(&s->pbctx, 32, s->avctx->frame_size); // No. of samples in the frame
> }
>
> +static void calc_predictor_params(AlacEncodeContext *s, int ch)
> +{
> + int32_t coefs[MAX_LPC_ORDER][MAX_LPC_ORDER];
> + int shift[MAX_LPC_ORDER];
> + int opt_order;
> +
> + opt_order = ff_lpc_calc_coefs(&s->dspctx, s->sample_buf[ch], s->avctx->frame_size, DEFAULT_MIN_PRED_ORDER, DEFAULT_MAX_PRED_ORDER,
> + ALAC_MAX_LPC_PRECISION, coefs, shift, 1, ORDER_METHOD_EST, ALAC_MAX_LPC_SHIFT, 1);
> +
> + s->lpc[ch].lpc_order = opt_order;
> + s->lpc[ch].lpc_quant = shift[opt_order-1];
> + memcpy(s->lpc[ch].lpc_coeff, coefs[opt_order-1], opt_order*sizeof(int));
> +}
> +
> static int estimate_stereo_mode(int32_t *left_ch, int32_t *right_ch, int n)
> {
> int i, best;
> @@ -147,7 +169,163 @@
> best = i;
> }
> }
> + return best;
> +}
>
> +static void alac_stereo_decorrelation(AlacEncodeContext *s)
> +{
> + int32_t *left = s->sample_buf[0], *right = s->sample_buf[1];
> + int i, mode, n = s->avctx->frame_size;
> + int32_t tmp;
> +
> + mode = estimate_stereo_mode(left, right, n);
> +
> + switch(mode)
> + {
> + case ALAC_CHMODE_LEFT_RIGHT:
> + s->interlacing_leftweight = 0;
> + s->interlacing_shift = 0;
> + break;
> +
> + case ALAC_CHMODE_LEFT_SIDE:
> + for(i=0; i<n; i++) {
> + right[i] = left[i] - right[i];
> + }
> + s->interlacing_leftweight = 1;
> + s->interlacing_shift = 0;
> + break;
> +
> + case ALAC_CHMODE_RIGHT_SIDE:
> + for(i=0; i<n; i++) {
> + tmp = right[i];
> + right[i] = left[i] - right[i];
> + left[i] = tmp + (right[i] >> 31);
> + }
> + s->interlacing_leftweight = 1;
> + s->interlacing_shift = 31;
> + break;
> +
> + default:
> + for(i=0; i<n; i++) {
> + tmp = left[i];
> + left[i] = (tmp + right[i]) >> 1;
> + right[i] = tmp - right[i];
> + }
> + s->interlacing_leftweight = 1;
> + s->interlacing_shift = 1;
> + break;
> + }
> +}
ok
> +
> +static void alac_linear_predictor(AlacEncodeContext *s, int ch)
> +{
> + int i;
> + LPCContext lpc = s->lpc[ch];
> +
> + if(lpc.lpc_order == 31) {
> + s->predictor_buf[0] = s->sample_buf[ch][0];
> +
> + for(i=1; i<s->avctx->frame_size; i++)
> + s->predictor_buf[i] = s->sample_buf[ch][i] - s->sample_buf[ch][i-1];
> +
> + return;
> + }
> +
> + // generalised linear predictor
> +
> + if(lpc.lpc_order > 0) {
> + int32_t *samples = s->sample_buf[ch];
> + int32_t *residual = s->predictor_buf;
> +
> + // generate warm-up samples
> + residual[0] = samples[0];
> + for(i=1;i<=lpc.lpc_order;i++)
> + residual[i] = samples[i] - samples[i-1];
> +
> + // perform lpc on remaining samples
> + for(i = lpc.lpc_order + 1; i < s->avctx->frame_size; i++) {
> + int sum = 0, res_val, j;
> +
> + for (j = 0; j < lpc.lpc_order; j++) {
> + sum += (samples[lpc.lpc_order-j] - samples[0]) *
> + lpc.lpc_coeff[j];
> + }
> + sum += (1 << (lpc.lpc_quant - 1));
the added value can be use instead of 0 to initialize sum
> + sum >>= lpc.lpc_quant;
> + sum += samples[0];
> + residual[i] = samples[lpc.lpc_order+1] - sum;
> + res_val = residual[i];
> +
> + if(res_val) {
> + int index = lpc.lpc_order - 1;
> + int neg = (res_val < 0);
> +
> + while(index >= 0 && (neg ? (res_val < 0):(res_val > 0))) {
> + int val = samples[0] - samples[lpc.lpc_order - index];
> + int sign = (val ? FFSIGN(val) : 0);
> +
> + if(neg)
> + sign*=-1;
> +
> + lpc.lpc_coeff[index] -= sign;
> + val *= sign;
> + res_val -= ((val >> lpc.lpc_quant) *
> + (lpc.lpc_order - index));
> + index--;
> + }
> + }
this part is also used in the decoder, thus could be factorized into
a common function
alac_entropy_coder() also has some common code with the decoder but it
is maybe too much interleaved with non-common code to factorize.
[...]
> @@ -226,6 +404,32 @@
> AV_WB8(alac_extradata+20, s->rc.k_modifier);
> }
>
> + if(avctx->min_prediction_order >= 0) {
> + if(avctx->min_prediction_order < MIN_LPC_ORDER ||
> + avctx->min_prediction_order > MAX_LPC_ORDER) {
> + av_log(avctx, AV_LOG_ERROR, "invalid min prediction order: %d\n", avctx->min_prediction_order);
> + return -1;
> + }
> +
> + s->min_prediction_order = avctx->min_prediction_order;
> + }
> +
> + if(avctx->max_prediction_order >= 0) {
> + if(avctx->max_prediction_order < MIN_LPC_ORDER ||
> + avctx->max_prediction_order > MAX_LPC_ORDER) {
> + av_log(avctx, AV_LOG_ERROR, "invalid max prediction order: %d\n", avctx->max_prediction_order);
> + return -1;
> + }
> +
> + s->max_prediction_order = avctx->max_prediction_order;
> + }
> +
> + if(s->max_prediction_order < s->min_prediction_order) {
> + av_log(avctx, AV_LOG_ERROR, "invalid prediction orders: min=%d max=%d\n",
> + s->min_prediction_order, s->max_prediction_order);
> + return -1;
> + }
> +
> avctx->extradata = alac_extradata;
> avctx->extradata_size = ALAC_EXTRADATA_SIZE;
>
> @@ -255,6 +459,9 @@
> return -1;
> }
>
> +verbatim:
> + init_put_bits(pb, frame, buf_size);
> +
> if((s->compression_level == 0) || verbatim_flag) {
> // Verbatim mode
> int16_t *samples = data;
ok
btw, if you want a svn write account, send diego your wanted username
and password (GPG encrypted!)
Assuming that you agree to our svn policy and are willing to maintain your
encoder after SOC.
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
There will always be a question for which you do not know the correct awnser.
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