Due to RKNN2 limitations with dynamic inputs, the sequence length is fixed at 1536. Audio speed scaling is used to compensate. The effect is acceptable when the difference isn't significant.
A Transpose operation within the RoPE (Rotary Positional Embedding) part of the DiT (Diffusion Transformer) model cannot run on the NPU, causing an approximate 15% decrease in inference speed. This could potentially be resolved by modifying the original model, but I chose not to, as inference would still be very slow due to the extremely long sequence length.
Only the DiT part utilizes the NPU; other parts run on the CPU. However, these CPU parts are fast and do not significantly impact the overall inference speed.