ac3dec.c

    }

    /* channel bandwidth */
    for (ch = 1; ch <= fbw_channels; ch++) {
        s->start_freq[ch] = 0;
        if (s->exp_strategy[blk][ch] != EXP_REUSE) {
            int group_size;
            int prev = s->end_freq[ch];
            if (s->channel_in_cpl[ch])
                s->end_freq[ch] = s->start_freq[CPL_CH];
            else if (s->channel_uses_spx[ch])
                s->end_freq[ch] = s->spx_src_start_freq;
            else {
                int bandwidth_code = get_bits(gbc, 6);
                if (bandwidth_code > 60) {
                    av_log(s->avctx, AV_LOG_ERROR, "bandwidth code = %d > 60\n", bandwidth_code);
                    return AVERROR_INVALIDDATA;
                }
                s->end_freq[ch] = bandwidth_code * 3 + 73;
            }
            group_size = 3 << (s->exp_strategy[blk][ch] - 1);
            s->num_exp_groups[ch] = (s->end_freq[ch] + group_size-4) / group_size;
            if (blk > 0 && s->end_freq[ch] != prev)
                memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
        }
    }
    if (cpl_in_use && s->exp_strategy[blk][CPL_CH] != EXP_REUSE) {
        s->num_exp_groups[CPL_CH] = (s->end_freq[CPL_CH] - s->start_freq[CPL_CH]) /
                                    (3 << (s->exp_strategy[blk][CPL_CH] - 1));
    }

    /* decode exponents for each channel */
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        if (s->exp_strategy[blk][ch] != EXP_REUSE) {
            s->dexps[ch][0] = get_bits(gbc, 4) << !ch;
            if (decode_exponents(gbc, s->exp_strategy[blk][ch],
                                 s->num_exp_groups[ch], s->dexps[ch][0],
                                 &s->dexps[ch][s->start_freq[ch]+!!ch])) {
                av_log(s->avctx, AV_LOG_ERROR, "exponent out-of-range\n");
                return AVERROR_INVALIDDATA;
            }
            if (ch != CPL_CH && ch != s->lfe_ch)
                skip_bits(gbc, 2); /* skip gainrng */
        }
    }

    /* bit allocation information */
    if (s->bit_allocation_syntax) {
        if (get_bits1(gbc)) {
            s->bit_alloc_params.slow_decay = ff_ac3_slow_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
            s->bit_alloc_params.fast_decay = ff_ac3_fast_decay_tab[get_bits(gbc, 2)] >> s->bit_alloc_params.sr_shift;
            s->bit_alloc_params.slow_gain  = ff_ac3_slow_gain_tab[get_bits(gbc, 2)];
            s->bit_alloc_params.db_per_bit = ff_ac3_db_per_bit_tab[get_bits(gbc, 2)];
            s->bit_alloc_params.floor  = ff_ac3_floor_tab[get_bits(gbc, 3)];
            for (ch = !cpl_in_use; ch <= s->channels; ch++)
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        } else if (!blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new bit allocation info must "
                   "be present in block 0\n");
            return AVERROR_INVALIDDATA;
        }
    }

    /* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */
    if (!s->eac3 || !blk) {
        if (s->snr_offset_strategy && get_bits1(gbc)) {
            int snr = 0;
            int csnr;
            csnr = (get_bits(gbc, 6) - 15) << 4;
            for (i = ch = !cpl_in_use; ch <= s->channels; ch++) {
                /* snr offset */
                if (ch == i || s->snr_offset_strategy == 2)
                    snr = (csnr + get_bits(gbc, 4)) << 2;
                /* run at least last bit allocation stage if snr offset changes */
                if (blk && s->snr_offset[ch] != snr) {
                    bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 1);
                }
                s->snr_offset[ch] = snr;

                /* fast gain (normal AC-3 only) */
                if (!s->eac3) {
                    int prev = s->fast_gain[ch];
                    s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];
                    /* run last 2 bit allocation stages if fast gain changes */
                    if (blk && prev != s->fast_gain[ch])
                        bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
                }
            }
        } else if (!s->eac3 && !blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new snr offsets must be present in block 0\n");
            return AVERROR_INVALIDDATA;
        }
    }

    /* fast gain (E-AC-3 only) */
    if (s->fast_gain_syntax && get_bits1(gbc)) {
        for (ch = !cpl_in_use; ch <= s->channels; ch++) {
            int prev = s->fast_gain[ch];
            s->fast_gain[ch] = ff_ac3_fast_gain_tab[get_bits(gbc, 3)];
            /* run last 2 bit allocation stages if fast gain changes */
            if (blk && prev != s->fast_gain[ch])
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        }
    } else if (s->eac3 && !blk) {
        for (ch = !cpl_in_use; ch <= s->channels; ch++)
            s->fast_gain[ch] = ff_ac3_fast_gain_tab[4];
    }

    /* E-AC-3 to AC-3 converter SNR offset */
    if (s->frame_type == EAC3_FRAME_TYPE_INDEPENDENT && get_bits1(gbc)) {
        skip_bits(gbc, 10); // skip converter snr offset
    }

    /* coupling leak information */
    if (cpl_in_use) {
        if (s->first_cpl_leak || get_bits1(gbc)) {
            int fl = get_bits(gbc, 3);
            int sl = get_bits(gbc, 3);
            /* run last 2 bit allocation stages for coupling channel if
               coupling leak changes */
            if (blk && (fl != s->bit_alloc_params.cpl_fast_leak ||
                sl != s->bit_alloc_params.cpl_slow_leak)) {
                bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
            }
            s->bit_alloc_params.cpl_fast_leak = fl;
            s->bit_alloc_params.cpl_slow_leak = sl;
        } else if (!s->eac3 && !blk) {
            av_log(s->avctx, AV_LOG_ERROR, "new coupling leak info must "
                   "be present in block 0\n");
            return AVERROR_INVALIDDATA;
        }
        s->first_cpl_leak = 0;
    }

    /* delta bit allocation information */
    if (s->dba_syntax && get_bits1(gbc)) {
        /* delta bit allocation exists (strategy) */
        for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {
            s->dba_mode[ch] = get_bits(gbc, 2);
            if (s->dba_mode[ch] == DBA_RESERVED) {
                av_log(s->avctx, AV_LOG_ERROR, "delta bit allocation strategy reserved\n");
                return AVERROR_INVALIDDATA;
            }
            bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
        }
        /* channel delta offset, len and bit allocation */
        for (ch = !cpl_in_use; ch <= fbw_channels; ch++) {
            if (s->dba_mode[ch] == DBA_NEW) {
                s->dba_nsegs[ch] = get_bits(gbc, 3) + 1;
                for (seg = 0; seg < s->dba_nsegs[ch]; seg++) {
                    s->dba_offsets[ch][seg] = get_bits(gbc, 5);
                    s->dba_lengths[ch][seg] = get_bits(gbc, 4);
                    s->dba_values[ch][seg]  = get_bits(gbc, 3);
                }
                /* run last 2 bit allocation stages if new dba values */
                bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
            }
        }
    } else if (blk == 0) {
        for (ch = 0; ch <= s->channels; ch++) {
            s->dba_mode[ch] = DBA_NONE;
        }
    }

    /* Bit allocation */
    for (ch = !cpl_in_use; ch <= s->channels; ch++) {
        if (bit_alloc_stages[ch] > 2) {
            /* Exponent mapping into PSD and PSD integration */
            ff_ac3_bit_alloc_calc_psd(s->dexps[ch],
                                      s->start_freq[ch], s->end_freq[ch],
                                      s->psd[ch], s->band_psd[ch]);
        }
        if (bit_alloc_stages[ch] > 1) {
            /* Compute excitation function, Compute masking curve, and
               Apply delta bit allocation */
            if (ff_ac3_bit_alloc_calc_mask(&s->bit_alloc_params, s->band_psd[ch],
                                           s->start_freq[ch],  s->end_freq[ch],
                                           s->fast_gain[ch],   (ch == s->lfe_ch),
                                           s->dba_mode[ch],    s->dba_nsegs[ch],
                                           s->dba_offsets[ch], s->dba_lengths[ch],
                                           s->dba_values[ch],  s->mask[ch])) {
                av_log(s->avctx, AV_LOG_ERROR, "error in bit allocation\n");
                return AVERROR_INVALIDDATA;
            }
        }
        if (bit_alloc_stages[ch] > 0) {
            /* Compute bit allocation */
            const uint8_t *bap_tab = s->channel_uses_aht[ch] ?
                                     ff_eac3_hebap_tab : ff_ac3_bap_tab;
            s->ac3dsp.bit_alloc_calc_bap(s->mask[ch], s->psd[ch],
                                      s->start_freq[ch], s->end_freq[ch],
                                      s->snr_offset[ch],
                                      s->bit_alloc_params.floor,
                                      bap_tab, s->bap[ch]);
        }
    }

    /* unused dummy data */
    if (s->skip_syntax && get_bits1(gbc)) {
        int skipl = get_bits(gbc, 9);
        while (skipl--)
            skip_bits(gbc, 8);
    }

    /* unpack the transform coefficients
       this also uncouples channels if coupling is in use. */
    decode_transform_coeffs(s, blk);

    /* TODO: generate enhanced coupling coordinates and uncouple */

    /* recover coefficients if rematrixing is in use */
    if (s->channel_mode == AC3_CHMODE_STEREO)
        do_rematrixing(s);

    /* apply scaling to coefficients (headroom, dynrng) */
    for (ch = 1; ch <= s->channels; ch++) {
        float gain = 1.0 / 4194304.0f;
        if (s->channel_mode == AC3_CHMODE_DUALMONO) {
            gain *= s->dynamic_range[2 - ch];
        } else {
            gain *= s->dynamic_range[0];
        }
        s->fmt_conv.int32_to_float_fmul_scalar(s->transform_coeffs[ch],
                                               s->fixed_coeffs[ch], gain, 256);
    }

    /* apply spectral extension to high frequency bins */
    if (s->spx_in_use && CONFIG_EAC3_DECODER) {
        ff_eac3_apply_spectral_extension(s);
    }

    /* downmix and MDCT. order depends on whether block switching is used for
       any channel in this block. this is because coefficients for the long
       and short transforms cannot be mixed. */
    downmix_output = s->channels != s->out_channels &&
                     !((s->output_mode & AC3_OUTPUT_LFEON) &&
                     s->fbw_channels == s->out_channels);
    if (different_transforms) {
        /* the delay samples have already been downmixed, so we upmix the delay
           samples in order to reconstruct all channels before downmixing. */
        if (s->downmixed) {
            s->downmixed = 0;
            ac3_upmix_delay(s);
        }

        do_imdct(s, s->channels);

        if (downmix_output) {
            s->ac3dsp.downmix(s->outptr, s->downmix_coeffs,
                              s->out_channels, s->fbw_channels, 256);
        }
    } else {
        if (downmix_output) {
            s->ac3dsp.downmix(s->xcfptr + 1, s->downmix_coeffs,
                              s->out_channels, s->fbw_channels, 256);
        }

        if (downmix_output && !s->downmixed) {
            s->downmixed = 1;
            s->ac3dsp.downmix(s->dlyptr, s->downmix_coeffs, s->out_channels,
                              s->fbw_channels, 128);
        }

        do_imdct(s, s->out_channels);
    }

    return 0;
}

/**
 * Decode a single AC-3 frame.
 */
static int ac3_decode_frame(AVCodecContext * avctx, void *data,
                            int *got_frame_ptr, AVPacket *avpkt)
{
    AVFrame *frame     = data;
    const uint8_t *buf = avpkt->data;
    int buf_size = avpkt->size;
    AC3DecodeContext *s = avctx->priv_data;
    int blk, ch, err, ret;
    const uint8_t *channel_map;
    const float *output[AC3_MAX_CHANNELS];

    /* copy input buffer to decoder context to avoid reading past the end
       of the buffer, which can be caused by a damaged input stream. */
    if (buf_size >= 2 && AV_RB16(buf) == 0x770B) {
        // seems to be byte-swapped AC-3
        int cnt = FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE) >> 1;
        s->dsp.bswap16_buf((uint16_t *)s->input_buffer, (const uint16_t *)buf, cnt);
    } else
        memcpy(s->input_buffer, buf, FFMIN(buf_size, AC3_FRAME_BUFFER_SIZE));
    buf = s->input_buffer;
    /* initialize the GetBitContext with the start of valid AC-3 Frame */
    init_get_bits(&s->gbc, buf, buf_size * 8);

    /* parse the syncinfo */
    err = parse_frame_header(s);

    if (err) {
        switch (err) {
        case AAC_AC3_PARSE_ERROR_SYNC:
            av_log(avctx, AV_LOG_ERROR, "frame sync error\n");
            return AVERROR_INVALIDDATA;
        case AAC_AC3_PARSE_ERROR_BSID:
            av_log(avctx, AV_LOG_ERROR, "invalid bitstream id\n");
            break;
        case AAC_AC3_PARSE_ERROR_SAMPLE_RATE:
            av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
            break;
        case AAC_AC3_PARSE_ERROR_FRAME_SIZE:
            av_log(avctx, AV_LOG_ERROR, "invalid frame size\n");
            break;
        case AAC_AC3_PARSE_ERROR_FRAME_TYPE:
            /* skip frame if CRC is ok. otherwise use error concealment. */
            /* TODO: add support for substreams and dependent frames */
            if (s->frame_type == EAC3_FRAME_TYPE_DEPENDENT || s->substreamid) {
                av_log(avctx, AV_LOG_WARNING, "unsupported frame type : "
                       "skipping frame\n");
                *got_frame_ptr = 0;
                return buf_size;
            } else {
                av_log(avctx, AV_LOG_ERROR, "invalid frame type\n");
            }
            break;
        case AAC_AC3_PARSE_ERROR_CRC:
        case AAC_AC3_PARSE_ERROR_CHANNEL_CFG:
            break;
        default: // Normal AVERROR do not try to recover.
            *got_frame_ptr = 0;
            return err;
        }
    } else {
        /* check that reported frame size fits in input buffer */
        if (s->frame_size > buf_size) {
            av_log(avctx, AV_LOG_ERROR, "incomplete frame\n");
            err = AAC_AC3_PARSE_ERROR_FRAME_SIZE;
        } else if (avctx->err_recognition & (AV_EF_CRCCHECK|AV_EF_CAREFUL)) {
            /* check for crc mismatch */
            if (av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, &buf[2],
                       s->frame_size - 2)) {
                av_log(avctx, AV_LOG_ERROR, "frame CRC mismatch\n");
                if (avctx->err_recognition & AV_EF_EXPLODE)
                    return AVERROR_INVALIDDATA;
                err = AAC_AC3_PARSE_ERROR_CRC;
            }
        }
    }

    /* if frame is ok, set audio parameters */
    if (!err) {
        avctx->sample_rate = s->sample_rate;
        avctx->bit_rate    = s->bit_rate;
    }

    /* channel config */
    if (!err || (s->channels && s->out_channels != s->channels)) {
        s->out_channels = s->channels;
        s->output_mode  = s->channel_mode;
        if (s->lfe_on)
            s->output_mode |= AC3_OUTPUT_LFEON;
        if (s->channels > 1 &&
            avctx->request_channel_layout == AV_CH_LAYOUT_MONO) {
            s->out_channels = 1;
            s->output_mode  = AC3_CHMODE_MONO;
        } else if (s->channels > 2 &&
                   avctx->request_channel_layout == AV_CH_LAYOUT_STEREO) {
            s->out_channels = 2;
            s->output_mode  = AC3_CHMODE_STEREO;
        }

        s->loro_center_mix_level   = gain_levels[s->  center_mix_level];
        s->loro_surround_mix_level = gain_levels[s->surround_mix_level];
        s->ltrt_center_mix_level   = LEVEL_MINUS_3DB;
        s->ltrt_surround_mix_level = LEVEL_MINUS_3DB;
        /* set downmixing coefficients if needed */
        if (s->channels != s->out_channels && !((s->output_mode & AC3_OUTPUT_LFEON) &&
                s->fbw_channels == s->out_channels)) {
            set_downmix_coeffs(s);
        }
    } else if (!s->channels) {
        av_log(avctx, AV_LOG_ERROR, "unable to determine channel mode\n");
        return AVERROR_INVALIDDATA;
    }
    avctx->channels = s->out_channels;
    avctx->channel_layout = avpriv_ac3_channel_layout_tab[s->output_mode & ~AC3_OUTPUT_LFEON];
    if (s->output_mode & AC3_OUTPUT_LFEON)
        avctx->channel_layout |= AV_CH_LOW_FREQUENCY;

    /* set audio service type based on bitstream mode for AC-3 */
    avctx->audio_service_type = s->bitstream_mode;
    if (s->bitstream_mode == 0x7 && s->channels > 1)
        avctx->audio_service_type = AV_AUDIO_SERVICE_TYPE_KARAOKE;

    /* get output buffer */
    frame->nb_samples = s->num_blocks * AC3_BLOCK_SIZE;
    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
        return ret;

    /* decode the audio blocks */
    channel_map = ff_ac3_dec_channel_map[s->output_mode & ~AC3_OUTPUT_LFEON][s->lfe_on];
    for (ch = 0; ch < AC3_MAX_CHANNELS; ch++) {
        output[ch] = s->output[ch];
        s->outptr[ch] = s->output[ch];
    }
    for (ch = 0; ch < s->channels; ch++) {
        if (ch < s->out_channels)
            s->outptr[channel_map[ch]] = (float *)frame->data[ch];
    }
    for (blk = 0; blk < s->num_blocks; blk++) {
        if (!err && decode_audio_block(s, blk)) {
            av_log(avctx, AV_LOG_ERROR, "error decoding the audio block\n");
            err = 1;
        }
        if (err)
            for (ch = 0; ch < s->out_channels; ch++)
                memcpy(((float*)frame->data[ch]) + AC3_BLOCK_SIZE*blk, output[ch], sizeof(**output) * AC3_BLOCK_SIZE);
        for (ch = 0; ch < s->out_channels; ch++)
            output[ch] = s->outptr[channel_map[ch]];
        for (ch = 0; ch < s->out_channels; ch++) {
            if (!ch || channel_map[ch])
                s->outptr[channel_map[ch]] += AC3_BLOCK_SIZE;
        }
    }

    av_frame_set_decode_error_flags(frame, err ? FF_DECODE_ERROR_INVALID_BITSTREAM : 0);

    /* keep last block for error concealment in next frame */
    for (ch = 0; ch < s->out_channels; ch++)
        memcpy(s->output[ch], output[ch], sizeof(**output) * AC3_BLOCK_SIZE);

    *got_frame_ptr = 1;

    return FFMIN(buf_size, s->frame_size);
}

/**
 * Uninitialize the AC-3 decoder.
 */
static av_cold int ac3_decode_end(AVCodecContext *avctx)
{
    AC3DecodeContext *s = avctx->priv_data;
    ff_mdct_end(&s->imdct_512);
    ff_mdct_end(&s->imdct_256);

    return 0;
}

#define OFFSET(x) offsetof(AC3DecodeContext, x)
#define PAR (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)
static const AVOption options[] = {
    { "drc_scale", "percentage of dynamic range compression to apply", OFFSET(drc_scale), AV_OPT_TYPE_FLOAT, {.dbl = 1.0}, 0.0, 1.0, PAR },

{"dmix_mode", "Preferred Stereo Downmix Mode", OFFSET(preferred_stereo_downmix), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, 2, 0, "dmix_mode"},
{"ltrt_cmixlev",   "Lt/Rt Center Mix Level",   OFFSET(ltrt_center_mix_level),    AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"ltrt_surmixlev", "Lt/Rt Surround Mix Level", OFFSET(ltrt_surround_mix_level),  AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_cmixlev",   "Lo/Ro Center Mix Level",   OFFSET(loro_center_mix_level),    AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},
{"loro_surmixlev", "Lo/Ro Surround Mix Level", OFFSET(loro_surround_mix_level),  AV_OPT_TYPE_FLOAT, {.dbl = -1.0 }, -1.0, 2.0, 0},

    { NULL},
};

static const AVClass ac3_decoder_class = {
    .class_name = "AC3 decoder",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};

AVCodec ff_ac3_decoder = {
    .name           = "ac3",
    .long_name      = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_AC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init           = ac3_decode_init,
    .close          = ac3_decode_end,
    .decode         = ac3_decode_frame,
    .capabilities   = CODEC_CAP_DR1,
    .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLTP,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class     = &ac3_decoder_class,
};

#if CONFIG_EAC3_DECODER
static const AVClass eac3_decoder_class = {
    .class_name = "E-AC3 decoder",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};

AVCodec ff_eac3_decoder = {
    .name           = "eac3",
    .long_name      = NULL_IF_CONFIG_SMALL("ATSC A/52B (AC-3, E-AC-3)"),
    .type           = AVMEDIA_TYPE_AUDIO,
    .id             = AV_CODEC_ID_EAC3,
    .priv_data_size = sizeof (AC3DecodeContext),
    .init           = ac3_decode_init,
    .close          = ac3_decode_end,
    .decode         = ac3_decode_frame,
    .capabilities   = CODEC_CAP_DR1,
    .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_FLTP,
                                                      AV_SAMPLE_FMT_NONE },
    .priv_class     = &eac3_decoder_class,
};
#endif