[FFmpeg-devel] [PATCH 1/2] avcodec: add HCOM decoder

[James Almer]

On 1/2/2019 3:53 PM, Paul B Mahol wrote:
> +static int hcom_decode(AVCodecContext *avctx, void *data,
> +                       int *got_frame, AVPacket *pkt)
> +{
> +    HCOMContext *s = avctx->priv_data;
> +    AVFrame *frame = data;
> +    GetByteContext gb;
> +    uint32_t current;
> +    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;
> +
> +    bytestream2_init(&gb, pkt->data, pkt->size);
> +    while (bytestream2_get_bytes_left(&gb) >= 4) {
> +        int bits = 32;
> +
> +        current = bytestream2_get_be32(&gb);
> +
> +        while (bits-- > 0) {
> +
> +            if (current & 0x80000000) {
> +                s->dict_entry = s->dict[s->dict_entry].r;
> +            } else {
> +                s->dict_entry = s->dict[s->dict_entry].l;
> +            }
> +
> +            current = current << 1;

This sounds like get_bits is a better fit than bytestream2 for this decoder.

> +            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;
> +}