pcm.c

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        for(;n>0;n--) {
            v = *samples++;
            *dst++ = (v >> 8) + 128;
        }
        break;
    case CODEC_ID_PCM_ZORK:
        for(;n>0;n--) {
            v= *samples++ >> 8;
            if(v<0)   v = -v;
            else      v+= 128;
            *dst++ = v;
        }
        break;
    case CODEC_ID_PCM_ALAW:
        for(;n>0;n--) {
            v = *samples++;
            *dst++ = linear_to_alaw[(v + 32768) >> 2];
        }
        break;
    case CODEC_ID_PCM_MULAW:
        for(;n>0;n--) {
            v = *samples++;
            *dst++ = linear_to_ulaw[(v + 32768) >> 2];
        }
        break;
    default:
        return -1;
    }
    //avctx->frame_size = (dst - frame) / (sample_size * avctx->channels);

    return dst - frame;
}

typedef struct PCMDecode {
    short table[256];
} PCMDecode;

static av_cold int pcm_decode_init(AVCodecContext * avctx)
{
    PCMDecode *s = avctx->priv_data;
    int i;

    switch(avctx->codec->id) {
    case CODEC_ID_PCM_ALAW:
        for(i=0;i<256;i++)
            s->table[i] = alaw2linear(i);
        break;
    case CODEC_ID_PCM_MULAW:
        for(i=0;i<256;i++)
            s->table[i] = ulaw2linear(i);
        break;
    default:
        break;
    }
    return 0;
}

/**
 * \brief convert samples to 16 bit
 * \param bps byte per sample for the source format, must be >= 2
 * \param le 0 for big-, 1 for little-endian
 * \param us 0 for signed, 1 for unsigned input
 * \param src input samples
 * \param samples output samples
 * \param src_len number of bytes in src
 */
static inline void decode_to16(int bps, int le, int us,
                               const uint8_t **src, short **samples, int src_len)
{
    int usum = us ? -0x8000 : 0;
    register int n = src_len / bps;
    if (le) *src += bps - 2;
    for(;n>0;n--) {
        register int v;
        if (le) v = AV_RL16(*src);
        else    v = AV_RB16(*src);
        v += usum;
        *(*samples)++ = v;
        *src += bps;
    }
    if (le) *src -= bps - 2;
}

static int pcm_decode_frame(AVCodecContext *avctx,
                            void *data, int *data_size,
                            const uint8_t *buf, int buf_size)
{
    PCMDecode *s = avctx->priv_data;
    int c, n;
    short *samples;
    const uint8_t *src, *src2[MAX_CHANNELS];

    samples = data;
    src = buf;

    if(avctx->channels <= 0 || avctx->channels > MAX_CHANNELS){
        av_log(avctx, AV_LOG_ERROR, "PCM channels out of bounds\n");
        return -1;
    }

    n = avctx->channels * av_get_bits_per_sample(avctx->codec_id)/8;
    /* av_get_bits_per_sample returns 0 for CODEC_ID_PCM_DVD */
    if (CODEC_ID_PCM_DVD == avctx->codec_id)
        /* 2 samples are interleaved per block in PCM_DVD */
        n = 2 * avctx->channels * avctx->bits_per_sample/8;

    if(n && buf_size % n){
        av_log(avctx, AV_LOG_ERROR, "invalid PCM packet\n");
        return -1;
    }

    buf_size= FFMIN(buf_size, *data_size/2);
    *data_size=0;

    n = buf_size/avctx->channels;
    for(c=0;c<avctx->channels;c++)
        src2[c] = &src[c*n];

    switch(avctx->codec->id) {
    case CODEC_ID_PCM_S32LE:
        decode_to16(4, 1, 0, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_S32BE:
        decode_to16(4, 0, 0, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_U32LE:
        decode_to16(4, 1, 1, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_U32BE:
        decode_to16(4, 0, 1, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_S24LE:
        decode_to16(3, 1, 0, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_S24BE:
        decode_to16(3, 0, 0, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_U24LE:
        decode_to16(3, 1, 1, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_U24BE:
        decode_to16(3, 0, 1, &src, &samples, buf_size);
        break;
    case CODEC_ID_PCM_S24DAUD:
        n = buf_size / 3;
        for(;n>0;n--) {
          uint32_t v = bytestream_get_be24(&src);
          v >>= 4; // sync flags are here
          *samples++ = ff_reverse[(v >> 8) & 0xff] +
                       (ff_reverse[v & 0xff] << 8);
        }
        break;
    case CODEC_ID_PCM_S16LE:
        n = buf_size >> 1;
        for(;n>0;n--) {
            *samples++ = bytestream_get_le16(&src);
        }
        break;
    case CODEC_ID_PCM_S16LE_PLANAR:
        for(n>>=1;n>0;n--)
            for(c=0;c<avctx->channels;c++)
                *samples++ = bytestream_get_le16(&src2[c]);
        src = src2[avctx->channels-1];
        break;
    case CODEC_ID_PCM_S16BE:
        n = buf_size >> 1;
        for(;n>0;n--) {
            *samples++ = bytestream_get_be16(&src);
        }
        break;
    case CODEC_ID_PCM_U16LE:
        n = buf_size >> 1;
        for(;n>0;n--) {
            *samples++ = bytestream_get_le16(&src) - 0x8000;
        }
        break;
    case CODEC_ID_PCM_U16BE:
        n = buf_size >> 1;
        for(;n>0;n--) {
            *samples++ = bytestream_get_be16(&src) - 0x8000;
        }
        break;
    case CODEC_ID_PCM_S8:
        n = buf_size;
        for(;n>0;n--) {
            *samples++ = *src++ << 8;
        }
        break;
    case CODEC_ID_PCM_U8:
        n = buf_size;
        for(;n>0;n--) {
            *samples++ = ((int)*src++ - 128) << 8;
        }
        break;
    case CODEC_ID_PCM_ZORK:
        n = buf_size;
        for(;n>0;n--) {
            int x= *src++;
            if(x&128) x-= 128;
            else      x = -x;
            *samples++ = x << 8;
        }
        break;
    case CODEC_ID_PCM_ALAW:
    case CODEC_ID_PCM_MULAW:
        n = buf_size;
        for(;n>0;n--) {
            *samples++ = s->table[*src++];
        }
        break;
    case CODEC_ID_PCM_DVD:
        if(avctx->bits_per_sample != 20 && avctx->bits_per_sample != 24) {
            av_log(avctx, AV_LOG_ERROR, "PCM DVD unsupported sample depth\n");
            return -1;
        } else {
            int jump = avctx->channels * (avctx->bits_per_sample-16) / 4;
            n = buf_size / (avctx->channels * 2 * avctx->bits_per_sample / 8);
            while (n--) {
                for (c=0; c < 2*avctx->channels; c++)
                    *samples++ = bytestream_get_be16(&src);
                src += jump;
            }
        }
        break;
    default:
        return -1;
    }
    *data_size = (uint8_t *)samples - (uint8_t *)data;
    return src - buf;
}

#ifdef CONFIG_ENCODERS
#define PCM_ENCODER(id,name,long_name_)         \
AVCodec name ## _encoder = {                    \
    #name,                                      \
    CODEC_TYPE_AUDIO,                           \
    id,                                         \
    0,                                          \
    pcm_encode_init,                            \
    pcm_encode_frame,                           \
    pcm_encode_close,                           \
    NULL,                                       \
    .long_name = NULL_IF_CONFIG_SMALL(long_name_), \
};
#else
#define PCM_ENCODER(id,name,long_name_)
#endif

#ifdef CONFIG_DECODERS
#define PCM_DECODER(id,name,long_name_)         \
AVCodec name ## _decoder = {                    \
    #name,                                      \
    CODEC_TYPE_AUDIO,                           \
    id,                                         \
    sizeof(PCMDecode),                          \
    pcm_decode_init,                            \
    NULL,                                       \
    NULL,                                       \
    pcm_decode_frame,                           \
    .long_name = NULL_IF_CONFIG_SMALL(long_name_), \
};
#else
#define PCM_DECODER(id,name,long_name_)
#endif

#define PCM_CODEC(id, name, long_name_)         \
    PCM_ENCODER(id,name,long_name_) PCM_DECODER(id,name,long_name_)

PCM_CODEC  (CODEC_ID_PCM_ALAW, pcm_alaw, "A-law PCM");
PCM_CODEC  (CODEC_ID_PCM_DVD, pcm_dvd, "signed 16|20|24-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_MULAW, pcm_mulaw, "mu-law PCM");
PCM_CODEC  (CODEC_ID_PCM_S8, pcm_s8, "signed 8-bit PCM");
PCM_CODEC  (CODEC_ID_PCM_S16BE, pcm_s16be, "signed 16-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_S16LE, pcm_s16le, "signed 16-bit little-endian PCM");
PCM_DECODER(CODEC_ID_PCM_S16LE_PLANAR, pcm_s16le_planar, "16-bit little-endian planar PCM");
PCM_CODEC  (CODEC_ID_PCM_S24BE, pcm_s24be, "signed 24-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_S24DAUD, pcm_s24daud, "D-Cinema audio signed 24-bit PCM");
PCM_CODEC  (CODEC_ID_PCM_S24LE, pcm_s24le, "signed 24-bit little-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_S32BE, pcm_s32be, "signed 32-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_S32LE, pcm_s32le, "signed 32-bit little-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_U8, pcm_u8, "unsigned 8-bit PCM");
PCM_CODEC  (CODEC_ID_PCM_U16BE, pcm_u16be, "unsigned 16-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_U16LE, pcm_u16le, "unsigned 16-bit little-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_U24BE, pcm_u24be, "unsigned 24-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_U24LE, pcm_u24le, "unsigned 24-bit little-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_U32BE, pcm_u32be, "unsigned 32-bit big-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_U32LE, pcm_u32le, "unsigned 32-bit little-endian PCM");
PCM_CODEC  (CODEC_ID_PCM_ZORK, pcm_zork, "Zork PCM");