void ff_mpeg_flush(AVCodecContext *avctx){
    int i;
    MpegEncContext *s = avctx->priv_data;

    if (!s || !s->picture)
        return;

    for (i = 0; i < MAX_PICTURE_COUNT; i++)
        ff_mpeg_unref_picture(s->avctx, &s->picture[i]);
    s->current_picture_ptr = s->last_picture_ptr = s->next_picture_ptr = NULL;

    ff_mpeg_unref_picture(s->avctx, &s->current_picture);
    ff_mpeg_unref_picture(s->avctx, &s->last_picture);
    ff_mpeg_unref_picture(s->avctx, &s->next_picture);

    s->mb_x= s->mb_y= 0;
    s->closed_gop= 0;

    s->parse_context.state= -1;
    s->parse_context.frame_start_found= 0;
    s->parse_context.overread= 0;
    s->parse_context.overread_index= 0;
    s->parse_context.index= 0;
    s->parse_context.last_index= 0;
    s->bitstream_buffer_size=0;
    s->pp_time=0;
}

The product dereferences a pointer that it expects to be valid but is NULL.