[FFmpeg-devel] [PATCH] ALS decoder

[Michael Niedermayer]

On Sun, Aug 30, 2009 at 12:03:32AM +0200, Thilo Borgmann wrote:
> Revision 13 attached.
> 
> Depends on ceillog2.rev3.patch.

[...]
> +/** Reads an ALSSpecificConfig from a buffer into the output struct.
> + */
> +static av_cold int read_specific_config(ALSDecContext *ctx)
> +{
> +    GetBitContext gb;
> +    uint64_t ht_size;
> +    int i, config_offset, crc_enabled;
> +    MPEG4AudioConfig m4ac;
> +    ALSSpecificConfig *sconf = &ctx->sconf;
> +    AVCodecContext *avctx    = ctx->avctx;
> +    const uint8_t *buffer    = avctx->extradata;
> +    uint32_t samples, als_id;
> +
> +    init_get_bits(&gb, buffer, avctx->extradata_size * 8);
> +
> +    config_offset = ff_mpeg4audio_get_config(&m4ac, buffer, avctx->extradata_size);
> +
> +    if (config_offset < 0)
> +        return -1;
> +
> +    skip_bits_long(&gb, config_offset);
> +
> +    if (get_bits_left(&gb) < (22 << 3))
> +        return -1;
> +
> +    // read the fixed items
> +    als_id                      = get_bits_long(&gb, 32);
> +    avctx->sample_rate          = m4ac.sample_rate;
> +    skip_bits_long(&gb, 32); // sample rate already known
> +    samples                     = get_bits_long(&gb, 32);
> +    avctx->channels             = m4ac.channels;
> +    skip_bits(&gb, 16);      // number of channels already knwon
> +    skip_bits(&gb, 3);       // skip file_type
> +    sconf->resolution           = get_bits(&gb, 3);
> +    sconf->floating             = get_bits1(&gb);
> +    skip_bits1(&gb);         // skip msb_first
> +    sconf->frame_length         = get_bits(&gb, 16) + 1;
> +    sconf->ra_distance          = get_bits(&gb, 8);
> +    sconf->ra_flag              = get_bits(&gb, 2);
> +    sconf->adapt_order          = get_bits1(&gb);
> +    sconf->coef_table           = get_bits(&gb, 2);
> +    sconf->long_term_prediction = get_bits1(&gb);
> +    sconf->max_order            = get_bits(&gb, 10);
> +    sconf->block_switching      = get_bits(&gb, 2);
> +    sconf->bgmc                 = get_bits1(&gb);
> +    sconf->sb_part              = get_bits1(&gb);
> +    sconf->joint_stereo         = get_bits1(&gb);
> +    sconf->mc_coding            = get_bits1(&gb);
> +    sconf->chan_config          = get_bits1(&gb);
> +    sconf->chan_sort            = get_bits1(&gb);
> +    crc_enabled                 = get_bits1(&gb);
> +    sconf->rlslms               = get_bits1(&gb);
> +    skip_bits(&gb, 5);       // skip 5 reserved bits
> +    skip_bits1(&gb);         // skip aux_data_enabled
> +
> +
> +    // check for ALSSpecificConfig struct
> +    if (als_id != MKBETAG('A','L','S','\0'))
> +        return -1;
> +
> +    ctx->cur_frame_length = sconf->frame_length;
> +
> +    // allocate quantized parcor coefficient buffer
> +    if (!(ctx->quant_cof = av_malloc(sizeof(*ctx->quant_cof) * sconf->max_order)) ||
> +        !(ctx->lpc_cof   = av_malloc(sizeof(*ctx->lpc_cof)   * sconf->max_order))) {
> +        av_log(avctx, AV_LOG_ERROR, "Allocating buffer memory failed.\n");
> +        return AVERROR(ENOMEM);
> +    }
> +    // calculate total number of frames to decode if possible
> +    if (samples != 0xFFFFFFFF) {
> +        ctx->num_frames        = (samples - 1) / sconf->frame_length + 1;
> +        ctx->last_frame_length = (samples - 1) % sconf->frame_length + 1;
> +    } else {
> +        ctx->num_frames        = 0;
> +        ctx->last_frame_length = 0;
> +    }
> +
> +    // read channel config
> +    if (sconf->chan_config) {
> +        if (get_bits_left(&gb) < 16)
> +            return -1;

later there must be at least 64 bits, so we can add 64 to the check at the
begin which then makes this one unneeded


> +
> +        sconf->chan_config_info = get_bits(&gb, 16);
> +        // TODO: use this to set avctx->channel_layout
> +    }
> +
> +
> +    // read channel sorting
> +    if (sconf->chan_sort && avctx->channels > 1) {
> +        int chan_pos_bits = av_ceil_log2(avctx->channels);
> +        int bits_needed  = avctx->channels * chan_pos_bits + 7;

> +        if (get_bits_left(&gb) < bits_needed)
> +            return -1;

possibly same


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you really think that XML is the answer, then you definitly missunderstood
the question -- Attila Kinali
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