try Movavi Flash Converter

Use Moyea FLV to Video Converter Pro 2 and it can help you convert FLV to MP4. It is easy to use and 2 or 3 steps are needed. 1. Import FLV to the software by clicking "Add FLV".2. Choose "MP4" format for output in "Export Format"convert flv to mp4 box.3. Specify output folder in "Export to...." by clicking the folder icon besides. 4. Click "Convert" tab and hit "Start" to begin converting. 5. Find the converted files in the specified output folder.
You can try Movavi Flash Converter, the ideal tool for downloading video from YouTube, Google and other popular video-sharing websites and converting Flash (.flv) videos to any format for any device. just copy and paste your online flv youtube download flv video into it, step by step guide:Output formats: AVI (DivX, XviD, etc), MPEG4 (iPod, MP4), 3GPP (GSM), 3GPP2 (CDMA), QuickTime (MOV), WMV, Flash (FLV), WMA or WAV.Hope it helps.