From experience, I can also recommend using SQLite as an application file format. I landed on SQLite after looking for solutions for a file format for an educational app we made for simulating biological neural networks. The app is cross-platform, written in Qt and the simulations needed to be stored as a JSON describing the network, a thumbnail and some metadata. It was also intended to be extensible with more features and backwards compatible if new versions were released. I considered creating our own simple format, using ZIP files, HDF5, Qt resource files or SQLite.
I landed on SQLite for many of the reasons outlined in this article and in particular because of how easy it was to implement and maintain. SQLite is supported natively in QtSql, which made it extremely easy to write the save and load functions, and later extend these with more data fields. In addition, we did not have to worry about cross-platform support since this was covered by SQLite and Qt already.
It may be a regional difference, but the link goes to a book narrated by Wil Wheaton for me. I found Wheaton's narration to be a great listen. He's not the slow-paced, calm narrator you will find in many other non-fiction audiobooks, but rather an enthusiastic storyteller. For this book, I think it was a good fit.
I landed on SQLite for many of the reasons outlined in this article and in particular because of how easy it was to implement and maintain. SQLite is supported natively in QtSql, which made it extremely easy to write the save and load functions, and later extend these with more data fields. In addition, we did not have to worry about cross-platform support since this was covered by SQLite and Qt already.