scaletempo.c

VLC Player Source Code

/*****************************************************************************
 * scaletempo.c: Scale audio tempo while maintaining pitch
 *****************************************************************************
 * Copyright © 2008 the VideoLAN team
 * $Id$
 *
 * Authors: Rov Juvano <[e-mail]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

/*****************************************************************************
 * Preamble
 *****************************************************************************/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <vlc_common.h>
#include <vlc_plugin.h>
#include <vlc_aout.h>

#include <string.h> /* for memset */
#include <limits.h> /* form INT_MIN */

/*****************************************************************************
 * Module descriptor
 *****************************************************************************/
static int  Open( vlc_object_t * );
static void Close( vlc_object_t * );
static void DoWork( aout_instance_t *, aout_filter_t *,
                    aout_buffer_t *, aout_buffer_t * );

vlc_module_begin();
    set_description( N_("Scale audio tempo in sync with playback rate") );
    set_shortname( N_("Scaletempo") );
    set_capability( "audio filter", 0 );
    set_category( CAT_AUDIO );
    set_subcategory( SUBCAT_AUDIO_AFILTER );

    add_integer_with_range( "scaletempo-stride", 30, 1, 2000, NULL,
        N_("Stride Length"), N_("Length in milliseconds to output each stride"), true );
    add_float_with_range( "scaletempo-overlap", .20, 0.0, 1.0, NULL,
        N_("Overlap Length"), N_("Percentage of stride to overlap"), true );
    add_integer_with_range( "scaletempo-search", 14, 0, 200, NULL,
        N_("Search Length"), N_("Length in milliseconds to search for best overlap position"), true );

    set_callbacks( Open, Close );
vlc_module_end();

/*
 * Scaletempo works by producing audio in constant sized chunks (a "stride") but
 * consuming chunks proportional to the playback rate.
 *
 * Scaletempo then smooths the output by blending the end of one stride with
 * the next ("overlap").
 *
 * Scaletempo smooths the overlap further by searching within the input buffer
 * for the best overlap position.  Scaletempo uses a statistical cross correlation
 * (roughly a dot-product).  Scaletempo consumes most of its CPU cycles here.
 *
 * NOTE:
 * sample: a single audio sample for one channel
 * frame: a single set of samples, one for each channel
 * VLC uses these terms differently
 */
typedef struct aout_filter_sys_t
{
    /* Filter static config */
    double    scale;
    /* parameters */
    unsigned  ms_stride;
    double    percent_overlap;
    unsigned  ms_search;
    /* audio format */
    unsigned  samples_per_frame;  /* AKA number of channels */
    unsigned  bytes_per_sample;
    unsigned  bytes_per_frame;
    unsigned  sample_rate;
    /* stride */
    double    frames_stride_scaled;
    double    frames_stride_error;
    unsigned  bytes_stride;
    double    bytes_stride_scaled;
    unsigned  bytes_queue_max;
    unsigned  bytes_queued;
    unsigned  bytes_to_slide;
    uint8_t  *buf_queue;
    /* overlap */
    unsigned  samples_overlap;
    unsigned  samples_standing;
    unsigned  bytes_overlap;
    unsigned  bytes_standing;
    void     *buf_overlap;
    void     *table_blend;
    void    (*output_overlap)( aout_filter_t *p_filter, void *p_out_buf, unsigned bytes_off );
    /* best overlap */
    unsigned  frames_search;
    void     *buf_pre_corr;
    void     *table_window;
    unsigned(*best_overlap_offset)( aout_filter_t *p_filter );
    /* for "audio filter" only, manage own buffers */
    int       i_buf;
    uint8_t  *p_buffers[2];
} aout_filter_sys_t;

/*****************************************************************************
 * best_overlap_offset: calculate best offset for overlap
 *****************************************************************************/
static unsigned best_overlap_offset_float( aout_filter_t *p_filter )
{
    aout_filter_sys_t *p = p_filter->p_sys;
    float *pw, *po, *ppc, *search_start;
    float best_corr = INT_MIN;
    unsigned best_off = 0;
    unsigned i, off;

    pw  = p->table_window;
    po  = p->buf_overlap;
    po += p->samples_per_frame;
    ppc = p->buf_pre_corr;
    for( i = p->samples_per_frame; i < p->samples_overlap; i++ ) {
      *ppc++ = *pw++ * *po++;
    }

    search_start = (float *)p->buf_queue + p->samples_per_frame;
    for( off = 0; off < p->frames_search; off++ ) {
      float corr = 0;
      float *ps = search_start;
      ppc = p->buf_pre_corr;
      for( i = p->samples_per_frame; i < p->samples_overlap; i++ ) {
        corr += *ppc++ * *ps++;
      }
      if( corr > best_corr ) {
        best_corr = corr;
        best_off  = off;
      }
      search_start += p->samples_per_frame;
    }

    return best_off * p->bytes_per_frame;
}

/*****************************************************************************
 * output_overlap: blend end of previous stride with beginning of current stride
 *****************************************************************************/
static void output_overlap_float( aout_filter_t   *p_filter,
                                  void            *buf_out,
                                  unsigned         bytes_off )
{
    aout_filter_sys_t *p = p_filter->p_sys;
    float *pout = buf_out;
    float *pb   = p->table_blend;
    float *po   = p->buf_overlap;
    float *pin  = (float *)( p->buf_queue + bytes_off );
    unsigned i;
    for( i = 0; i < p->samples_overlap; i++ ) {
        *pout++ = *po - *pb++ * ( *po - *pin++ ); po++;
    }
}

/*****************************************************************************
 * fill_queue: fill p_sys->buf_queue as much possible, skipping samples as needed
 *****************************************************************************/
static size_t fill_queue( aout_filter_t *p_filter,
                          uint8_t       *p_buffer,
                          size_t         i_buffer,
                          size_t         offset )
{
    aout_filter_sys_t *p = p_filter->p_sys;
    unsigned bytes_in = i_buffer - offset;
    size_t offset_unchanged = offset;

    if( p->bytes_to_slide > 0 ) {
        if( p->bytes_to_slide < p->bytes_queued ) {
            unsigned bytes_in_move = p->bytes_queued - p->bytes_to_slide;
            memmove( p->buf_queue,
                     p->buf_queue + p->bytes_to_slide,
                     bytes_in_move );
            p->bytes_to_slide = 0;
            p->bytes_queued   = bytes_in_move;
        } else {
            unsigned bytes_in_skip;
            p->bytes_to_slide -= p->bytes_queued;
            bytes_in_skip      = __MIN( p->bytes_to_slide, bytes_in );
            p->bytes_queued    = 0;
            p->bytes_to_slide -= bytes_in_skip;
            offset            += bytes_in_skip;
            bytes_in          -= bytes_in_skip;
        }
    }

    if( bytes_in > 0 ) {
        unsigned bytes_in_copy = __MIN( p->bytes_queue_max - p->bytes_queued, bytes_in );
        memcpy( p->buf_queue + p->bytes_queued,
                p_buffer + offset,
                bytes_in_copy );
        p->bytes_queued += bytes_in_copy;
        offset          += bytes_in_copy;
    }

    return offset - offset_unchanged;
}

/*****************************************************************************
 * transform_buffer: main filter loop
 *****************************************************************************/
static size_t transform_buffer( aout_filter_t   *p_filter,
                                uint8_t         *p_buffer,
                                size_t           i_buffer,
                                uint8_t         *pout )
{
    aout_filter_sys_t *p = p_filter->p_sys;

    size_t offset_in = fill_queue( p_filter, p_buffer, i_buffer, 0 );
    unsigned bytes_out = 0;
    while( p->bytes_queued >= p->bytes_queue_max ) {
        unsigned bytes_off = 0;

        // output stride
        if( p->output_overlap ) {
            if( p->best_overlap_offset ) {
                bytes_off = p->best_overlap_offset( p_filter );
            }
            p->output_overlap( p_filter, pout, bytes_off );
        }
        memcpy( pout + p->bytes_overlap,
                p->buf_queue + bytes_off + p->bytes_overlap,
                p->bytes_standing );
        pout += p->bytes_stride;
        bytes_out += p->bytes_stride;

        // input stride
        memcpy( p->buf_overlap,
                p->buf_queue + bytes_off + p->bytes_stride,
                p->bytes_overlap );
        double frames_to_slide = p->frames_stride_scaled + p->frames_stride_error;
        unsigned frames_to_stride_whole = (int)frames_to_slide;
        p->bytes_to_slide       = frames_to_stride_whole * p->bytes_per_frame;
        p->frames_stride_error  = frames_to_slide - frames_to_stride_whole;

        offset_in += fill_queue( p_filter, p_buffer, i_buffer, offset_in );
    }

    return bytes_out;
}

/*****************************************************************************
 * calculate_output_buffer_size