The process explained uses two very useful programs for researchers working with audio and video: Audacity (free) and QuickTime Pro (under €30 and well worth it). You should be able to carry out similar processes with other programs available.
Step 1: Cut the audio
NOTE: Often the sound files that audio recorders generate are not compatible with QuickTime Pro. If you are able to open your audio file with QuickTime Pro, you can cut it following the instructions for cutting video. If not, use Audacity to cut it and export it in a format that QuickTime will accept.
1. Open Audacity. Select file → open. Search for the audio file you would like to add to your video. The program imports the file and creates a soundwave.
2. We need to cut the audio so that it starts right on the clap of your hands. To do this, click the button that looks like a double sided T (circled in the image). Then, hold down the mouse button and drag it across the soundwave to select the part you want to eliminate (everything before the clap). You can zoom in to be more precise. Then, click edit → cut.
3. Once the soundwave starts and ends exactly where you want it to, select file → export (we recommend you export as .wav as this will be compatible with QuickTime Pro and most other video editing programs). Say where you want to save the cut audio.
Step 2: Cut the video
1.Open QuickTime Pro. Select file → open. Search for the video file you would like to add your audio to.
2. To cut part of the video, click your mouse and drag it along the time bar to select the part of the video that you want to delete. Then select edit → cut.
3. Finally, click file → save and the program will create a .mov file where you tell it to.
Step 3: Add the audio to the video
1. Open the new audio file with QuickTime Pro.
2. Select all the audio by clicking edit → select all (ctrl-a) and copy it by clicking edit → copy (ctrl+c).
3. Now open the new video file with QuickTime Pro.
4. Place your cursor at the very beginning of the player bar. Select edit → add to movie (→+ctrl+v).By doing this, you have added your new soundtrack to the video.
5. Finally, you need to delete the old audio from the video. Select window → show movie properties (ctrl+j). Select soundtrack 1, and click delete.
6. Save the synchronised file, ready for transcribing.