av_cold void ff_mpv_idct_init(MpegEncContext *s)
{
    if (s->codec_id == AV_CODEC_ID_MPEG4)
        s->idsp.mpeg4_studio_profile = s->studio_profile;
    ff_idctdsp_init(&s->idsp, s->avctx);

    /* load & permutate scantables
     * note: only wmv uses different ones
     */
    if (s->alternate_scan) {
        ff_init_scantable(s->idsp.idct_permutation, &s->inter_scantable, ff_alternate_vertical_scan);
        ff_init_scantable(s->idsp.idct_permutation, &s->intra_scantable, ff_alternate_vertical_scan);
    } else {
        ff_init_scantable(s->idsp.idct_permutation, &s->inter_scantable, ff_zigzag_direct);
        ff_init_scantable(s->idsp.idct_permutation, &s->intra_scantable, ff_zigzag_direct);
    }
    ff_init_scantable(s->idsp.idct_permutation, &s->intra_h_scantable, ff_alternate_horizontal_scan);
    ff_init_scantable(s->idsp.idct_permutation, &s->intra_v_scantable, ff_alternate_vertical_scan);
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.