FFmpeg/libavfilter/af_apad.c

/*
 * Copyright (c) 2012 Michael Niedermayer
 *
 * 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
 *
 */

/**
 * @file
 * audio pad filter.
 *
 * Based on af_aresample.c
 */

#include "libavutil/avstring.h"
#include "libavutil/channel_layout.h"
#include "libavutil/opt.h"
#include "libavutil/samplefmt.h"
#include "libavutil/avassert.h"
#include "avfilter.h"
#include "audio.h"
#include "internal.h"

typedef struct {
    int64_t next_pts;
} APadContext;

static av_cold int init(AVFilterContext *ctx, const char *args)
{
    APadContext *apad = ctx->priv;

    apad->next_pts = AV_NOPTS_VALUE;

    return 0;
}

static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *frame)
{
    AVFilterContext *ctx = inlink->dst;
    APadContext *apad = ctx->priv;
    apad->next_pts = frame->pts + av_rescale_q(frame->audio->nb_samples, (AVRational){1, inlink->sample_rate}, inlink->time_base);
    return ff_filter_frame(ctx->outputs[0], frame);
}

static int request_frame(AVFilterLink *outlink)
{
    AVFilterContext *ctx = outlink->src;
    APadContext *apad = ctx->priv;
    int ret;

    ret = ff_request_frame(ctx->inputs[0]);

    if (ret == AVERROR_EOF) {
        int n_out = 4096;
        AVFilterBufferRef *outsamplesref = ff_get_audio_buffer(outlink, AV_PERM_WRITE, n_out);
        if (!outsamplesref)
            return AVERROR(ENOMEM);

        av_assert0(outsamplesref->audio->sample_rate == outlink->sample_rate);
        av_assert0(outsamplesref->audio->nb_samples  == n_out);

        av_samples_set_silence(outsamplesref->extended_data, 0,
                               n_out,
                               outsamplesref->audio->channels,
                               outsamplesref->format);

        outsamplesref->pts = apad->next_pts;
        if (apad->next_pts != AV_NOPTS_VALUE)
            apad->next_pts += av_rescale_q(n_out, (AVRational){1, outlink->sample_rate}, outlink->time_base);

        return ff_filter_frame(outlink, outsamplesref);
    }
    return ret;
}

static const AVFilterPad apad_inputs[] = {
    {
        .name         = "default",
        .type         = AVMEDIA_TYPE_AUDIO,
        .filter_frame = filter_frame,
        .min_perms    = AV_PERM_READ,
    },
    { NULL },
};

static const AVFilterPad apad_outputs[] = {
    {
        .name          = "default",
        .request_frame = request_frame,
        .type          = AVMEDIA_TYPE_AUDIO,
    },
    { NULL },
};

AVFilter avfilter_af_apad = {
    .name          = "apad",
    .description   = NULL_IF_CONFIG_SMALL("Pad audio with silence."),
    .init          = init,
    .priv_size     = sizeof(APadContext),
    .inputs        = apad_inputs,
    .outputs       = apad_outputs,
};