To join video files, you can use VideoToolBox or YouTube Editor online for free. But you need to notice the file limitation and network speed. For desktop software, you'll get a mass of results after inputing the keywords "free video joiner", "video joiner freeware" or "video combiner" in Google. All these video joiner software have a common and simple process to join videos together. Usually, it needs 3 steps: import videos > rearrange the order > start to combine videos. However, you have to use some professional video editors if you need more requirement.
If you have a bunch of video and music files with low volume, this user-friendly video volume booster, as well as an audio volume booster, allows you not only to increase video volume but also to increase audio volume in a single batch process for sharing and playback on various portable devices. Download and install this video volume booster on your PC, then launch it.
Import video or music files which you want to increase sound volume into this program. Select output format and enter Setting window, you'll see a loudspeaker icon in Audio category. Drag the slider up to 200% to boost audio volume. Start to increase volume of video and music files in batches after done. Similarly, you can repeat the process as an MP3 volume booster.