FFmpeg/libavcodec/hcom.c

/*
 * HCOM audio decoder
 *
 * 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/intreadwrite.h"

#include "avcodec.h"
#include "get_bits.h"
#include "internal.h"

typedef struct HEntry {
    int16_t l, r;
} HEntry;

typedef struct HCOMContext {
    AVCodecContext *avctx;

    uint8_t first_sample;
    uint8_t sample;
    int dict_entries;
    int dict_entry;
    int delta_compression;

    HEntry *dict;
} HCOMContext;

static av_cold int hcom_init(AVCodecContext *avctx)
{
    HCOMContext *s = avctx->priv_data;

    if (avctx->channels != 1) {
        av_log(avctx, AV_LOG_ERROR, "invalid number of channels\n");
        return AVERROR_INVALIDDATA;
    }

    if (avctx->extradata_size <= 7)
        return AVERROR_INVALIDDATA;
    s->dict_entries = AV_RB16(avctx->extradata);
    if (avctx->extradata_size < s->dict_entries * 4 + 7)
        return AVERROR_INVALIDDATA;
    s->delta_compression = AV_RB32(avctx->extradata + 2);
    s->sample = s->first_sample = avctx->extradata[avctx->extradata_size - 1];

    s->dict = av_calloc(s->dict_entries, sizeof(*s->dict));
    if (!s->dict)
        return AVERROR(ENOMEM);
    for (int i = 0; i < s->dict_entries; i++) {
        s->dict[i].l = AV_RB16(avctx->extradata + 6 + 4 * i);
        s->dict[i].r = AV_RB16(avctx->extradata + 6 + 4 * i + 2);
    }

    avctx->sample_fmt = AV_SAMPLE_FMT_U8;
    s->dict_entry = 0;

    return 0;
}

static int hcom_decode(AVCodecContext *avctx, void *data,
                       int *got_frame, AVPacket *pkt)
{
    HCOMContext *s = avctx->priv_data;
    AVFrame *frame = data;
    GetBitContext gb;
    int ret, n = 0;

    if (pkt->size > INT16_MAX)
        return AVERROR_INVALIDDATA;

    frame->nb_samples = pkt->size * 8;
    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
        return ret;

    if ((ret = init_get_bits8(&gb, pkt->data, pkt->size)) < 0)
        return ret;

    while (get_bits_left(&gb) > 0) {
        if (get_bits1(&gb))
            s->dict_entry = s->dict[s->dict_entry].r;
        else
            s->dict_entry = s->dict[s->dict_entry].l;

        if (s->dict[s->dict_entry].l < 0) {
            int16_t datum;

            datum = s->dict[s->dict_entry].r;

            if (!s->delta_compression)
                s->sample = 0;
            s->sample = (s->sample + datum) & 0xFF;

            frame->data[0][n++] = s->sample;

            s->dict_entry = 0;
        }
    }

    frame->nb_samples = n;

    *got_frame = 1;

    return pkt->size;
}

static av_cold int hcom_close(AVCodecContext *avctx)
{
    HCOMContext *s = avctx->priv_data;

    av_freep(&s->dict);

    return 0;
}

AVCodec ff_hcom_decoder = {
    .name           = "hcom",
    .long_name      = NULL_IF_CONFIG_SMALL("HCOM Audio"),
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_HCOM,
    .priv_data_size = sizeof(HCOMContext),
    .init           = hcom_init,
    .close          = hcom_close,
    .decode         = hcom_decode,
    .capabilities   = AV_CODEC_CAP_DR1,
};