Function decode_frame

libavcodec/alsdec.c:1380–1444

Decodes an ALS frame. */

/** Decodes an ALS frame.
 */
static int decode_frame(AVCodecContext *avctx,
                        void *data, int *data_size,
                        AVPacket *avpkt)
{
    ALSDecContext *ctx       = avctx->priv_data;
    ALSSpecificConfig *sconf = &ctx->sconf;
    const uint8_t *buffer    = avpkt->data;
    int buffer_size          = avpkt->size;
    int invalid_frame, size;
    unsigned int c, sample, ra_frame, bytes_read, shift;

    init_get_bits(&ctx->gb, buffer, buffer_size * 8);

    // In the case that the distance between random access frames is set to zero
    // (sconf->ra_distance == 0) no frame is treated as a random access frame.
    // For the first frame, if prediction is used, all samples used from the
    // previous frame are assumed to be zero.
    ra_frame = sconf->ra_distance && !(ctx->frame_id % sconf->ra_distance);

    // the last frame to decode might have a different length
    if (sconf->samples != 0xFFFFFFFF)
        ctx->cur_frame_length = FFMIN(sconf->samples - ctx->frame_id * (uint64_t) sconf->frame_length,
                                      sconf->frame_length);
    else
        ctx->cur_frame_length = sconf->frame_length;

    // decode the frame data
    if ((invalid_frame = read_frame_data(ctx, ra_frame) < 0))
        av_log(ctx->avctx, AV_LOG_WARNING,
               "Reading frame data failed. Skipping RA unit.\n");

    ctx->frame_id++;

    // check for size of decoded data
    size = ctx->cur_frame_length * avctx->channels *
           (av_get_bits_per_sample_format(avctx->sample_fmt) >> 3);

    if (size > *data_size) {
        av_log(avctx, AV_LOG_ERROR, "Decoded data exceeds buffer size.\n");
        return -1;
    }

    *data_size = size;

    // transform decoded frame into output format
    #define INTERLEAVE_OUTPUT(bps)                                 \
    {                                                              \
        int##bps##_t *dest = (int##bps##_t*) data;                 \
        shift = bps - ctx->avctx->bits_per_raw_sample;             \
        for (sample = 0; sample < ctx->cur_frame_length; sample++) \
            for (c = 0; c < avctx->channels; c++)                  \
                *dest++ = ctx->raw_samples[c][sample] << shift;    \
    }

    if (ctx->avctx->bits_per_raw_sample <= 16) {
        INTERLEAVE_OUTPUT(16)
    } else {
        INTERLEAVE_OUTPUT(32)