Although you can use the in5 Video interactive widget to show either a big play button with no controller or a full controller, you can also use it to set the controller to None and make your own Play and Stop buttons. 
If you'd like to make your Play button start the video and then appear to turn into a Stop button, you can make 2 buttons and apply the Show/Hide Buttons and Forms action. 


Here's how:
  1. Make the Play button by making artwork within InDesign and converting it to a button using the Buttons and Forms panel (Window > Interactive > Buttons and Forms).
  2. Make the Stop button.
  3. Add the video to the layout by selecting File > Place and choosing a .mp4 with H.264 encoding.
  4. Select the Play button and add the following actions in the Buttons and Forms panel to trigger playback of the video and set the buttons to match that state...
    • Event: On Release or Tap
    • Actions: 
      • Video
        • Video: [name of placed video]
        • Options: Play
      • Show /Hide Buttons and Forms
        • Visibility: 
          • Hide (eyeball with slash) Play
          • Show (eyeball) Stop
  5. Select the Stop button and add the following actions in the Buttons and Forms panel
    • Event: On Release or Tap
    • Actions: 
      • Video
        • Video: [name of placed video]
        • Options: Stop
      • Show /Hide Buttons and Forms
        • Visibility:
          • Show (eyeball) Play
          • Hide (eyeball with slash ) Stop
  6. Align the Play and Stop buttons so that they overlap (with Show/Hide Buttons and Forms, the overlapping buttons will work)


With in5, navigating to the previous or next page will automatically stop the video. If you're using in5's Back and Next arrows, you could replace them with your own buttons that not only advance to the previous or next page but also reset your video buttons. 


Instead of using the Show Back/Next Arrows option in the Basic section of the Export HTML5 with in5 dialog, create your own buttons for navigation. Then add either a Go To Previous Page or Go To Next Page action and a Show /Hide Buttons and Forms action with the settings in Step 5 above. If you add that action, then the user can go forward or back, the video will automatically stop, and the buttons will be reset.


Alternatively, instead of using Hide/Show Buttons—you could put the buttons using Object States and that will automatically be reset to the first state by in5 when the page changes. In that case, you could use the default in5 Back/Next Arrows as well.