Multimodal link prediction on multimodal knowledge graphs is an inference task aimed at finding missing triples, which seeks to improve prediction accuracy by leveraging a wide range of information. However, current multimodal knowledge graph link prediction methods are primarily designed in the spatial domain, necessitating ever-growing complexity in fusion strategies. In addition, most of them focus on only three modalities (text, image, and structure). Forward-looking approaches, however, should accommodate a broader array of modalities. Motivated by the operational simplification enabled by transforming features into the frequency (or time-frequency) domain, we propose a wavelet-transform-based multimodal link prediction method, WFF, which offers high modal extensibility and low fusion complexity. Specifically, for unimodal information, we designed a Unimodal Time-Frequency Knowledge Enhancement module, UTFKE, which extracts time-frequency features via discrete wavelet transform and enhances information quality through adaptive filtering. To address the challenge of multimodal fusion, we devised a Multimodal Time-Frequency Knowledge Fusion module MTFKF that supports high modal extensibility and enables effective, efficient integration. Extensive experiments on multiple well-known datasets demonstrate that WFF outperforms strong baselines and achieves state-of-the-art performance. In addition, WFF extends modality to audio and video, further validating the model's effectiveness. Our code is available at https://github.com/xxd12315/WFF.