Text-based search using video speech transcripts is a popular approach for granular video retrieval at the shot or story level. However, misalignment of speech and visual tracks, speech transcription errors, and other characteristics of video content pose unique challenges for this video retrieval approach. In this paper, we explore several automatic query refinement methods to address these issues. We consider two query expansion methods based on pseudo-relevance feedback and one query refinement method based on semantic text annotation. We evaluate these approaches in the context of the TRECVID 2005 Video Retrieval Benchmark using a baseline approach without any refinement. To improve robustness, we also consider a query-independent fusion approach. We show that this combined approach can outperform the baseline for most query topics, with improvements of up to 40%. We also show that query-dependent fusion approaches can potentially improve the results further, leading to 18-75% gains when tuned with optimal fusion parameters.