MTS format is a high-definition MPEG, AVC, H.264 transport stream video file format which commonly used by HD camcorders such as Sony, Canon, Panasonic.
MTS file is not playable on iPhone 4 unless you convert the MTS video to iPhone 4 supported formats. To import these MTS videos to iPhone 4 for convenient playback or easy sharing, you need a third-part MTS to iPhone 4 Converter. Here we recommend Cucusoft DVD to iPhone 4 Converter Suite, which is a powerful Video to iPhone 4 Converter Suite to convert both DVD and videos to iPhone 4 easily and quickly.
Following is a step by step guide on how to convert MTS to iPhone 4 on Windows system. For Mac user, here is iPhone 4 Converter for Mac for you to convert MTS video to iPhone 4 on Mac computer.
Step 1: Download and Run
Free download and install Cucusoft DVD to iPhone 4 Converter Suite via the link below, then run it.
Step 2: Open file
Select iPhone Video Converter and load the MTS video files you want to convert to iPhone 4 by clicking "Open file".

Step 3: Settings
Click the drop-down list of " Profile" to select either MPEG4(.MP4) or H.264 as the output format, and then click "Output" to browse your computer hard disk to specify the location to store the converted file.

Step 4: Convert and Transfer
When all settings done, click "Convert" to start to convert MTS to iPhone 4. And the last thing you need to do is to transfer the converted files to iTunes and then sync them to iPhone 4, Done!
Now with this guide, you can convert MTS video to iPhone 4 and play MTS on iPhone 4 freely. Besides, you can also convert MOV to iPhone 4, Convert FLV to iPhone 4, etc. by using the Cucusoft iPhone 4 Converter Suite. Free download and have a try by yourself now!