Please confirm the information below first.
1. iTunes version is 18.104.22.168 or later.
2. iTunes runs normally, iTunes store can be connected normally, videos can be played by iTunes normally, there is no prompt of expired certificate or session timeout.
3. The prompt box is closed when you convert a unauthorized video, if not, all conversions will fail.
4. The internet connection is fine.
5. Quick Time is installed if your computer is with 32-bit system and integrated graphics(for Windows version).
If above are confirmed, please contact us with the following information.
1. Total converted video size.
2. The video names you are converting.
3. Simultaneously converted video quantity.
4. Other operations with the program while conversion.
5. Click top Settings>Help>Bug Report, and submit Bug Report.