The ep128emu format TAP files are basically 1-bit audio files.
There are two versions of the format: the older and simpler version has no header and uses a fixed sample rate of 24000 Hz (one cycle of the leader tone, sync bit, 0 bit, and 1 bit is 10, 16, 12, and 8 samples, respectively). The samples are encoded in most significant bit first order. The EXOS cassette data format is documented in the
technical information at page 83 of the PDF file.
The more advanced ep128emu TAP format begins with a 4096 bytes header, which contains 1024 32-bit integers in MSB first format. The first 4 of these are: 0x0275CD72, 0x1C445126, bits per sample (must be 1, 2, 4, or 8, but only 1 is useful in practice), and the sample rate in Hz. The remaining 1020 values are markers, a table of positions on the tape in samples (not bytes), unused entries are set to 0xFFFFFFFF. The markers usually indicate the starting positions of the files on the tape, so that it is possible to easily find them in the emulator (Alt+, and Alt+.).
The EPTE tape format consists of a 512 bytes long header, and then all the EXOS format cassette data as raw bytes (not audio), except the leader tones and sync bits are not included. So, the emulator needs to synthesize the audio from this data. In the header, at an offset of 128 bytes, there is always the 32 bytes long string "ENTERPRISE 128K TAPE FILE ". The rest of the header contains the starting position (in bytes, relative to the beginning of the cassette data) of each chunk as 32-bit LSB first integers. Thus, the first 128 bytes of the header is a table of 32 chunk positions. However, this is followed by the "ENTERPRISE 128K TAPE FILE " string, so it is not clear if more than 32 chunks are possible by continuing the table after skipping these 32 bytes. Fortunately, most programs (except some large ones usually loaded from disk) do not need more than 32 chunks. To play one chunk as audio, the emulator generates the leader tone and the sync bit, and then the raw data bytes, which are encoded in least significant bit first order.