Function decode

libavcodec/mimic.c:246–308

}

static int decode(MimicContext *ctx, int quality, int num_coeffs,
                  int is_iframe)
{
    int ret, y, x, plane, cur_row = 0;

    for (plane = 0; plane < 3; plane++) {
        const int is_chroma = !!plane;
        const int qscale    = av_clip(10000 - quality, is_chroma ? 1000 : 2000,
                                      10000) << 2;
        const int stride    = ctx->frames[ctx->cur_index ].f->linesize[plane];
        uint8_t       *dst  = ctx->frames[ctx->cur_index ].f->data[plane];
        /* src is unused for I frames; set to avoid UB pointer arithmetic. */
        const uint8_t *src  = is_iframe ? dst : ctx->frames[ctx->prev_index].f->data[plane];

        for (y = 0; y < ctx->num_vblocks[plane]; y++) {
            for (x = 0; x < ctx->num_hblocks[plane]; x++) {
                /* Check for a change condition in the current block.
                 * - iframes always change.
                 * - Luma plane changes on get_bits1 == 0
                 * - Chroma planes change on get_bits1 == 1 */
                if (is_iframe || get_bits1(&ctx->gb) == is_chroma) {
                    /* Luma planes may use a backreference from the 15 last
                     * frames preceding the previous. (get_bits1 == 1)
                     * Chroma planes don't use backreferences. */
                    if (is_chroma || is_iframe || !get_bits1(&ctx->gb)) {
                        if ((ret = vlc_decode_block(ctx, num_coeffs,
                                                    qscale)) < 0) {
                            av_log(ctx->avctx, AV_LOG_ERROR, "Error decoding "
                                   "block.\n");
                            return ret;
                        }
                        ctx->idsp.idct_put(dst, stride, ctx->dct_block);
                    } else {
                        unsigned int backref = get_bits(&ctx->gb, 4);
                        int index            = (ctx->cur_index + backref) & 15;

                        if (index != ctx->cur_index && ctx->frames[index].f) {
                            const uint8_t *p = ctx->frames[index].f->data[0];
                            ff_progress_frame_await(&ctx->frames[index], cur_row);
                            p += src -
                                 ctx->frames[ctx->prev_index].f->data[plane];
                            ctx->hdsp.put_pixels_tab[1][0](dst, p, stride, 8);
                        } else {
                            av_log(ctx->avctx, AV_LOG_ERROR,
                                     "No such backreference! Buggy sample.\n");
                        }
                    }
                } else {
                    ff_progress_frame_await(&ctx->frames[ctx->prev_index], cur_row);
                    ctx->hdsp.put_pixels_tab[1][0](dst, src, stride, 8);
                }
                src += 8;
                dst += 8;
            }
            src += (stride - ctx->num_hblocks[plane]) << 3;
            dst += (stride - ctx->num_hblocks[plane]) << 3;

            ff_progress_frame_report(&ctx->frames[ctx->cur_index], cur_row++);