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.aac file or click "+ Add Files" to browse. Multiple files queue for batch trimming, and everything stays in your browser tab — no upload to a third-party server.00:00:15 and duration 00:00:30 keeps seconds 15 through 45). Leave duration blank to trim from the start point to the end of the file..aac downloads automatically — no sign-up, no watermark, no email gate.AAC (Advanced Audio Coding) is the default audio format for iTunes, Apple Music, YouTube, most podcast platforms, and audio extracted from MP4/MOV video. AAC is standardized as MPEG-2 Part 7 (1997) and MPEG-4 Part 3 (1999), and at the same bitrate it sounds noticeably cleaner than MP3 — Wikipedia notes "hi-fi transparency demands data rates of at least 128 kbit/s" for AAC, where MP3 needs 192 kbps for similar transparency. Trimming the file directly keeps it native: no MP3 transcode, no quality loss, no decoder mismatch on Apple hardware.
.m4r ringtone files at 40 seconds (text tones at 30 seconds); trimming a chorus or hook to 25–30 seconds and renaming the extension to .m4r is the simplest path. Files longer than 40 seconds import but never appear in Settings → Sounds → Ringtone..m4a/AAC by default).yt-dlp -x and most rip tools default to AAC inside an .m4a container; trim out intros, sponsor reads, or pre-roll ads before archiving.| Property | AAC | MP3 | M4A | Opus | FLAC |
|---|---|---|---|---|---|
| Standard | MPEG-2 Pt 7 / MPEG-4 Pt 3 | MPEG-1 Audio Layer III | MPEG-4 container (usually AAC) | RFC 6716 | Free Lossless Audio Codec |
| Compression | Lossy | Lossy | Lossy (AAC inside) | Lossy | Lossless |
| Quality at 128 kbps | Transparent for most listeners | Audible artifacts on cymbals/sibilants | Same as AAC | Better than AAC at low bitrate | N/A (lossless) |
| Sample-rate range | 8–96 kHz | 16–48 kHz | 8–96 kHz | 8–48 kHz | up to 655 kHz |
| Native on iPhone/iTunes | Yes | Yes | Yes | No (third-party apps) | No (third-party apps) |
| Native on Android | Yes (since 2.3) | Yes | Yes | Yes (since 5.0) | Yes (since 3.1) |
| Typical use | Streaming, broadcast, mobile | Universal music, legacy | Apple music/audiobooks | Voice, web, gaming | Archival, hi-fi |
| Use case | Bitrate (CBR) | Sample rate | Channels |
|---|---|---|---|
| Speech / podcast / audiobook | 64–96 kbps | 22050–44100 Hz | Mono |
| Voice memo / dictation | 32–64 kbps | 16000–22050 Hz | Mono |
| Music (good quality) | 128–192 kbps | 44100 Hz | Stereo |
| Music (transparent) | 256 kbps | 44100 Hz | Stereo |
| iTunes Plus / Apple Music download | 256 kbps | 44100 Hz | Stereo |
| Video soundtrack | 128–192 kbps | 48000 Hz | Stereo |
| iPhone ringtone (M4R, ≤40 s) | 128–192 kbps | 44100 Hz | Stereo |
The xconvert trimmer decodes the AAC frames inside your trim window and re-encodes at the bitrate and quality preset you select, so a small generation loss occurs. Pick "Quality Preset: Highest" or match the source bitrate (right-click the original in Finder/Explorer to see it) to keep the loss inaudible — AAC is robust against a single re-encode at 192 kbps or higher. If you need bit-exact frame-level cuts with zero re-encoding, the only path is ffmpeg -c copy from the command line, and it can only cut on existing AAC frame boundaries (~21 ms granularity).
Trim the section you want to 30 seconds or less (Apple enforces a 40-second limit for ringtones and 30 seconds for text tones), then rename the .aac or .m4a extension to .m4r and drag it into the Finder sidebar under your iPhone → General → Tones (macOS Catalina and later) or import via iTunes on Windows. Files longer than 40 seconds import successfully but never appear in the Settings → Sounds → Ringtone picker.
AAC is the codec; M4A is a container (MPEG-4 Part 14) that almost always holds AAC audio. A .m4a file renamed to .aac plays identically on most players because the bitstream is the same. Apple uses .m4a for Apple Music and iTunes downloads, .m4b for audiobooks (with chapter markers and resume position), and .m4r for ringtones. If you need a raw AAC stream (for Android or older Bluetooth speakers), trim to .aac; if you need iTunes metadata and album art, convert to M4A.
Mono for any single-voice recording — interviews, podcasts, voice memos, audiobooks. It halves the file size at the same perceptual quality because the encoder isn't allocating bits to a phantom second channel. Use Stereo for music, multi-mic recordings, and anything mixed with panning or stereo effects. Switching a stereo music track to mono will sum L+R and may cancel out side-channel content (reverbs, vocal doubles), so check the result before keeping it.
44100 Hz is the safe default — it's CD-quality and matches almost every music source. Use 48000 Hz when the AAC came from video (MP4, MOV, broadcast TV) so it stays in sync without resampling. Drop to 22050 Hz or 16000 Hz for pure speech to halve the file again. Avoid going above the source rate; resampling 44100 → 96000 Hz adds zero quality and roughly doubles the file size.
Standard ID3v2-style tags (title, artist, album, year) and embedded album art carry through. Chapter markers in .m4b audiobooks and timed-lyrics tracks are usually rebuilt against the new shorter timeline; if you need exact chapter preservation, trim into .m4b rather than .aac. DRM-protected files from older iTunes purchases (.m4p) cannot be trimmed by any browser-based tool — only the Apple Music app on a authorized device can play them.
You can enter trim points down to milliseconds (HH:MM:SS.ms format), but AAC encodes audio in fixed-size frames of 1024 samples each — that's about 21.3 ms at 48 kHz or 23.2 ms at 44.1 kHz. The encoder snaps to the nearest frame boundary, so a request for 00:00:10.005 may resolve to 00:00:10.000 or 00:00:10.023. For most practical work (ringtones, podcast clips, samples), this is invisible. If you need sample-accurate edits for music production, work in WAV inside a DAW and export to AAC at the end.
Drop several .aac files into the queue and the same start/duration applies to each — useful for batch-trimming a folder of voice memos to remove identical leading silence. To join two clips end-to-end, trim each separately then use Audio Cutter for sequential merging, or convert both to a common format first.
Keep AAC for anything iPhone, iPad, Mac, Android (2.3+), Sonos, modern car infotainment, and most Bluetooth headphones — they all decode AAC natively and a transcode to MP3 only loses quality. Switch to MP3 for legacy Windows Media Player, very old MP3 players (pre-2008 iPods aside, which support AAC), some treadmill/elliptical USB ports, and FAT32 USB sticks meant for cars built before 2010. For lossless archival pick FLAC; for editing in a DAW pick WAV.