I think I have a two solutions to your question.
Method 1 requires multiple renders but no key framing:
1. Import your image into the timeline. Enter size and position and set the size to 101.0. (This protects against a black line in between your clips). Exit to timeline.
2. Duplicate the first clip twice so now you have three clips. Double click the second clip a click the flip horizontally icon. Exit to timeline.
3. Apply the “push left” or Push right” transition between the first and second clip, and again between the second and third clip. On the push left transition in between the second and third clip, adjust left side of the push left transition so the effect is one second and two frames short of your project frame rate (1.28 long in a 30fps timeline, 1.58 in 60fps, 1.22 in 24 etc.). On the push left transition in between the first and second clip, adjust right side of the push left transition to one second and two frames short of your project frame rate.
4. Export video to photos. Open a new project. Import the video to the main track.
5. Cut the video to remove every frame in the beginning before the motion starts, and the two frames in between the first and second clip where the motion stops. In the third clip, cut off the frame that is identical to the first frame of your project and every frame after that.
5. Now you should have two clips on your timeline. Duplicate the first and second clips and paste them at the end of your project. If you cut everything correctly, when you play the project you should have an nice loop that repeats twice. If not adjust the frames you cut until the loop is smooth.
6. Delete the duplicated clips so now there are two clips on your timeline again and export the video to photos for the second time.
7. Open a new project, drop in the second exported video as many times as you’d like the video to loop. Export your final project, and import it into your the video you’ve been making.
8. Finish your video and show me.
A second, more time consuming metho that uses fewer renders and is smooth method:
1. Import your image once to the first track, extend it to 4 seconds and duplicate it to the second track and third track.
2. Enter size and position keyfaming for the the first clip. Move the play head to 1 second and turn on key framing (thus making a key frame). Move the play head to 2 seconds, and adjust the position to -200. A key frame will be created automatically. Exit back to the timeline
3. Select the second clip and enter size and position key framing. Move the play head to 0 seconds and flip the image on the track. Move the play head to 2 seconds and make a key frame. Move the play head back to 0 and set the x position to +200. Move the play head to 1 second and set the x position to +200. Move the play head to 3 seconds and set the x position to -200. Exit to timeline.
4.Select the third clip and enter size and position key framing. Move the play head to 3 seconds and make a key frame. Move the play head to 2 seconds and adjust the x position to +200. Move the play head to 0 seconds and adjust the x position to +200.
5. Export the video to photos, open a new project, drop in the exported video in as many times as you’d like the video to loop. Export your final project, and import it into your the video you’ve been making.
8. Finish your video and show me.
Thank you for your question I enjoyed figuring it out!
#godanglego