FileUtils::getinstance()->getDataFromFile(const char* path).getBytes() returns nil for a .m4a file

Form a sql blob i get audio data, i write a .aac file and play it. Works fine. Then i trim .aac file and get a .m4a file and play it works fine. this is done in iOS wrapper.
In c++ i get data with this method FileUtils::getinstance()->getDataFromFile(const char* path) from trimmed .m4a file but the Bytes component is empty while the sieze_t component returns the perfect size. in case of non-trimmed .aac file even Bytes give the right value.

Can anyone help?