Qtractor is a MP3 & Audio software developed by Rui Nuno Capela. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Qtractor:

MarydownEditor: Qtractor is an Audio/MIDI multi-track sequencer application written in C++ with the Qt4 framework. Target platform is Linux, where the Jack Audio Connection Kit (JACK) for audio, and the Advanced Linux Sound Architecture (ALSA) for MIDI, are the main infrastructures to evolve as a fairly-featured Linux desktop Audio Workstation GUI, specially dedicated to the personal home-studio.

Features
Multi-track audio and MIDI sequencing and recording.
Developed on pure Qt4 C++ application framework (no Qt3 nor KDE dependencies).
Uses JACK for audio and ALSA sequencer for MIDI as multimedia infrastructures.
Traditional multi-track tape recorder control paradigm.
Audio file formats support: OGG (via libvorbis), MP3 (via libmad, playback only), WAV, FLAC, AIFF and many, many more (via Libsndfile).
Standard MIDI files support (format 0 and 1).
Non-destructive, non-linear editing.
Unlimited number of tracks per session/project.
Unlimited number of overlapping clips per track.
XML encoded session/project description files (SDI).
Point-and-click, multi-select, drag-and-drop interaction (drag, MOVE, drop, cut, Copy, paste, paste-repeat, delete, split, merge)
Unlimited undo/redo.
Built-in mixer and monitor controls.
Built-in connection patchbay control and persistence (a-la QjackCtl).
LADSPA, DSSI and native VSTi plug-in support.
Unlimited number of plug-ins per track or bus.
Plug-in presets, programs and chunk/configurations support.
Unlimited audio effect send/return inserts per track or bus.
Audio/MIDI clip fade-in/out (linear, quadratic, cubic).
Audio/MIDI clip gain/volume, normalize, export.
Audio clip time-stretching (WSOLA-like or via librubberband), pitch-shifting (via librubberband) and seamless sample-rate conversion (via libsamplerate).
Audio/MIDI track export (mix-down, merge).
Audio/MIDI metronome bar/beat clicks.
Unlimited tempo/time-signature map.
MIDI clip editor (matrix/piano roll).
MIDI instrument definitions.