In essence, h264 to aiff conversion describes the export of audio track from H.264 video to AIFF - Audio Interchange File Format.
Various movie / video editing tools usually offer tools for management of audio tracks in video files, so these apps are your best options. Not every may support export to AIFF format, but you can always use another tool to get the content in this format. What matters is the ability to extract the audio content in first place.
Some multimedia converters advertise such conversion possible as well, so in case of free tools it might be worth the shot.
Updated: January 3, 2024