Hi Antonio, The zstd compression format allows for skippable frames https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#skippable-frames
pzstd uses this and puts the skippable frame at the beginning of the file. The function test_format in zutils.cc doesn't take this magic_number into account and so reports the file as uncompressed. Thank you, Chris Jamboretz
