[FFmpeg-devel] [PATCH] ALAC Encoder

Jai Menon realityman
Tue Aug 19 16:33:56 CEST 2008


Hi,

On Tuesday 19 Aug 2008 2:08:32 am Michael Niedermayer wrote:
> 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.
>

Yeah, I agree with the policy and I'll definitely be working on the encoder as 
well as some other stuff too after SoC.

Also, till I do get the account, could somebody please commit the ok'ed hunks 
here and some in the followup mail :-)
Thanks.

Regards,

Jai Menon




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