Software⏱️ 4 min read📅 2026-06-11

How to Fix: FFmpeg error "track X: codec frame size is not set"

FFmpeg error: track X: codec frame size is not set. Solution involves specifying codec framesize for audio tracks in FFmpeg command.

Quick Answer: Specify the codec framesize for each audio track using the -vf 'scale=640:-1' option, e.g., '-map 0:v -map 1:a -c:v copy -c:a copy -vf 'scale=640:-1' %~nF_trimmed.mp4'

📋 Table of Contents

  1. 🛑 Root Causes of the Error
  2. 🔧 Proven Troubleshooting Steps
  3. ✨ Wrapping Up

The error 'track X: codec frame size is not set' appears when FFmpeg is unable to determine the correct frame size for one or both of the audio tracks in an MP4 file. This issue affects users who are trying to trim their MP4 files using FFmpeg, resulting in incomplete or distorted audio.

This error can be frustrating because it prevents the user from completing the trimming process, and it may also result in damaged video files. However, by following the steps outlined below, you should be able to resolve this issue and successfully trim your MP4 files.

🛑 Root Causes of the Error

  • The primary reason for this error is that FFmpeg requires the codec frame size to be set for each audio track before it can proceed with the trimming process. If the codec frame size is not set, FFmpeg will throw an error and stop processing the file.
  • Another possible cause of this error is if the MP4 file contains multiple audio tracks, but only one of them has a valid codec frame size set. In this case, FFmpeg may not be able to determine the correct frame size for the other audio tracks, resulting in the 'track X: codec frame size is not set' error.

🔧 Proven Troubleshooting Steps

Resolving the Error by Specifying Audio Tracks

  1. Step 1: To resolve this issue, you need to specify which audio tracks you want FFmpeg to use when trimming your MP4 file. You can do this using the '-map' option followed by the track numbers or '0:v' and '0:a' for both video and audio tracks respectively.
  2. Step 2: For example, if your MP4 file has one video track and two audio tracks, you would specify '-map 0:v -map 1:a -c:v copy -c:a copy %~nF_trimmed.mp4'. This tells FFmpeg to use the first audio track (track 1) when trimming the file.
  3. Step 3: By specifying the correct audio tracks, you can ensure that FFmpeg has enough information to determine the correct frame size and complete the trimming process successfully.

Resolving the Error using -af

  1. Step 1: Another way to resolve this issue is by using the '-af' option followed by a script that sets the codec frame size for each audio track. For example, you can use the following command: 'ffmpeg -sseof -20 -i %F -af aresample=async=1:sample_rate=44100 -c:v copy -c:a copy %~nF_trimmed.mp4'. This script sets the sample rate to 44.1 kHz for each audio track, which is a common setting for MP3 files.
  2. Step 2: By using this option, you can force FFmpeg to set the codec frame size for each audio track, even if it's not present in the original file.

✨ Wrapping Up

In conclusion, the 'track X: codec frame size is not set' error occurs when FFmpeg is unable to determine the correct frame size for one or both of the audio tracks in an MP4 file. By specifying which audio tracks you want FFmpeg to use or using the '-af' option with a script that sets the codec frame size, you should be able to resolve this issue and successfully trim your MP4 files.

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