The AEPX file extension is used by the Adobe After Effects video compositing and animation software for XML-based project files. In addition to references to videos, audio files and images, AEPX files also contain cut and timeline information and effects settings.
Usually, the paths to the media files are also saved, so that they are only found if they are in the original directory. But you can also load AEPX files and specify new locations for missing files.
AEPX files contain almost exclusively readable information, so that, for example, changed paths or media names can be easily adapted via text editor. Aepx project files are designed primarily for automated (via script) modification of project settings.
Adobe expressly points out that AEPX should not be used primarily for projects. Therefore, AEPX files can only be saved under 'File -> Save as XML'. In addition, AEPX files can be quite large and are then processed slower.
The AEPX format is supported since version CS4.