Convert MKV to MP4 with FFmpeg on Linux

Converting video files from MKV to MP4 on a Linux system is a frequent task for users seeking better compatibility with media players, web browsers, and mobile devices. This article provides a quick overview of the most efficient FFmpeg commands to accomplish this container swap. You will learn the fastest method to convert files without losing video quality, as well as how to re-encode the file if your specific playback device requires a different video codec.

The Fastest Method: Stream Copy (No Re-encoding)

The most efficient way to convert an MKV file to MP4 is to copy the existing video and audio streams directly into the new container. Because this method does not re-encode the video, it takes only a few seconds and preserves 100% of the original quality.

To perform a stream copy, open your Linux terminal and run the following command:

ffmpeg -i input.mkv -c copy output.mp4

Command Breakdown

• ffmpeg: Installs and invokes the FFmpeg tool.
• -i input.mkv: Specifies the path to your original MKV input file.
• -c copy: Instructs FFmpeg to copy both the video and audio streams directly without re-encoding them.
• output.mp4: Specifies the desired name for your new MP4 file.

The Compatible Method: Full Re-encoding

While the stream copy method is fast, it relies on the MP4 container supporting the underlying codecs used in the original MKV file. If your target device does not support the original formats (such as high-end audio formats like DTS or specific video codecs), you will need to re-encode the file to standard H.264 video and AAC audio.

To re-encode the video for maximum compatibility, use this command:

ffmpeg -i input.mkv -c:v libx264 -c:a aac output.mp4

Command Breakdown

• -c:v libx264: Encodes the video stream using the widely compatible H.264 codec.
• -c:a aac: Encodes the audio stream using the standard AAC codec, which ensures playback on almost any modern device.