Avidemux+cannot+use+that+file+as+audio+track May 2026

If you are trying to use a FLAC or Opus file as an external track, you must change your output format to MKV . MP4 does not support FLAC natively.

One of the most common frustrations users face is the dreaded red banner or pop-up stating: You’ve selected an external audio file (like an MP3, WAV, or AAC) to replace or merge with your video’s audio, but Avidemux refuses to cooperate. Why? And more importantly, how do you fix it? avidemux+cannot+use+that+file+as+audio+track

Temporarily change Video Output to Mpeg4 ASP (Xvid) or Mpeg4 AVC (x264) and set Configure to Constant Rate Factor = 22 . Then add the audio. If it works, the original video’s structure was broken. (You will have to re-encode the video, which is slow.) The Duration Mismatch If your external audio file is shorter or longer than the video by a fraction of a second, Avidemux’s copy mode may panic. If you are trying to use a FLAC

Avidemux is a beloved tool in the video editing world for one simple reason: it’s fast, free, and perfect for cutting, filtering, and re-encoding video without the bloat of professional suites like Premiere Pro or DaVinci Resolve. However, its simplicity has a downside. When something goes wrong, the error messages can be cryptic, unhelpful, and infuriating. Then add the audio

Go to Format dropdown in the main toolbar and select MKV V2 or MKV . Then try adding your external audio track again. Avidemux’s "Copy" mode hates Variable Bitrate (VBR) MP3 files. When you cut video on keyframes, VBR audio loses sync because the bitrate fluctuates. Avidemux is old-school; it prefers Constant Bitrate (CBR).

Convert your VBR MP3 to CBR MP3 or PCM WAV using a tool like Audacity or FFmpeg before loading it into Avidemux.