You have downloaded some MP4 or MKV video files.
You want to extract audio parts so that you could copy them to your iPhone to listen to them while turning off the display of your phone.
- Download this portable application for your Windows.
- Use it to convert the MP4 or MKV files to MP3 files. You can also extract the original audio (for example M4A format) if needed.
- Copy the MP3 files to your phone.