PIFF - Protected Interoperable File Format - is used for transmitting video and audio via streams. It is also the file format used in PlayReady DRM. It is an ISO Base Media File Format brand (ISO 14496-12), so the library can essentially read ISO media files, including MP4 (some additions might be needed).

The library was created to read and write PIFF files for Smooth Streaming data protected with PlayReady (CENC). When writing, there is a number of hard-coded values, mostly flags related to MP4 format and audio / video tracks. For instance, it is expected, that the stream has 1 video (H.264) and 1 audio (AAC-L) track.

The process is:

• Write the header PiffWriter.WriteHeader(). Use PiffReader.GetTrackId() to retrieve the track IDs from the data and put it into PiffManifest. A helper method PiffWriter.GetDuration() might also come handy.
• Append the data fragments (which are essentially moof boxes) as they are downloaded. Use PiffReader.GetFragmentSequenceNumber() to make sure the fragments come in increasing sequence order. Keep the fragment offsets in the output file for the footer.
• Write the footer PiffWriter.WriteFooter().

Simple reading:

// Parse all boxes. "mdat" are parsed, but their data is discarded,
// and shall be retrieved later using either Position property or
// location boxes.
var inputFile = PiffFile.ParseAll(inputStream);

// Parse until PiffMovieBox is fully parsed, ignore the rest.
var inputFile = PiffFile.ParseUntil(inputStream, b => b is PiffMovieBox);