af_dcshift.c

/*
 * Copyright (c) 2000 Chris Ausbrooks <weed@bucket.pp.ualr.edu>
 * Copyright (c) 2000 Fabien COELHO <fabien@coelho.net>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "libavutil/opt.h"
#include "libavutil/samplefmt.h"
#include "avfilter.h"
#include "audio.h"
#include "filters.h"

typedef struct DCShiftContext {
    const AVClass *class;
    double dcshift;
    double limiterthreshold;
    double limitergain;
} DCShiftContext;

#define OFFSET(x) offsetof(DCShiftContext, x)
#define A AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM

static const AVOption dcshift_options[] = {
    { "shift",       "set DC shift",     OFFSET(dcshift),       AV_OPT_TYPE_DOUBLE, {.dbl=0}, -1, 1, A },
    { "limitergain", "set limiter gain", OFFSET(limitergain), AV_OPT_TYPE_DOUBLE, {.dbl=0}, 0, 1, A },
    { NULL }
};

AVFILTER_DEFINE_CLASS(dcshift);

static av_cold int init(AVFilterContext *ctx)
{
    DCShiftContext *s = ctx->priv;

    s->limiterthreshold = INT32_MAX * (1.0 - (fabs(s->dcshift) - s->limitergain));

    return 0;
}

static int filter_frame(AVFilterLink *inlink, AVFrame *in)
{
    AVFilterContext *ctx = inlink->dst;
    AVFilterLink *outlink = ctx->outputs[0];
    AVFrame *out;
    DCShiftContext *s = ctx->priv;
    int i, j;
    double dcshift = s->dcshift;

    if (av_frame_is_writable(in)) {
        out = in;
    } else {
        out = ff_get_audio_buffer(outlink, in->nb_samples);
        if (!out) {
            av_frame_free(&in);
            return AVERROR(ENOMEM);
        }
        av_frame_copy_props(out, in);
    }

    if (s->limitergain > 0) {
        for (i = 0; i < inlink->ch_layout.nb_channels; i++) {
            const int32_t *src = (int32_t *)in->extended_data[i];
            int32_t *dst = (int32_t *)out->extended_data[i];

            for (j = 0; j < in->nb_samples; j++) {
                double d;

                d = src[j];

                if (d > s->limiterthreshold && dcshift > 0) {
                    d = (d - s->limiterthreshold) * s->limitergain /
                             (INT32_MAX - s->limiterthreshold) +
                             s->limiterthreshold + dcshift;
                } else if (d < -s->limiterthreshold && dcshift < 0) {
                    d = (d + s->limiterthreshold) * s->limitergain /
                             (INT32_MAX - s->limiterthreshold) -
                             s->limiterthreshold + dcshift;
                } else {
                    d = dcshift * INT32_MAX + d;
                }

                dst[j] = av_clipl_int32(d);
            }
        }
    } else {
        for (i = 0; i < inlink->ch_layout.nb_channels; i++) {
            const int32_t *src = (int32_t *)in->extended_data[i];
            int32_t *dst = (int32_t *)out->extended_data[i];

            for (j = 0; j < in->nb_samples; j++) {
                double d = dcshift * (INT32_MAX + 1.) + src[j];

                dst[j] = av_clipl_int32(d);
            }
        }
    }

    if (out != in)
        av_frame_free(&in);
    return ff_filter_frame(outlink, out);
}
static const AVFilterPad dcshift_inputs[] = {
    {
        .name         = "default",
        .type         = AVMEDIA_TYPE_AUDIO,
        .filter_frame = filter_frame,
    },
};

const FFFilter ff_af_dcshift = {
    .p.name         = "dcshift",
    .p.description  = NULL_IF_CONFIG_SMALL("Apply a DC shift to the audio."),
    .p.priv_class   = &dcshift_class,
    .p.flags        = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC,
    .priv_size      = sizeof(DCShiftContext),
    .init           = init,
    FILTER_INPUTS(dcshift_inputs),
    FILTER_OUTPUTS(ff_audio_default_filterpad),
    FILTER_SINGLE_SAMPLEFMT(AV_SAMPLE_FMT_S32P),
};