How to repair incorrect movie metadata?

Understanding Metadata in Video Files

Metadata is data about data. In the context of video files, it includes information such as the title, author, creation date, and custom tags like genre or album art. Media players and library managers like Plex, Kodi, or VLC rely on this embedded information to organize and display your content. When metadata is missing, corrupted, or incorrectly formatted, your videos may appear with generic names or fail to group correctly.

The most common issue arises when files are ripped from discs or downloaded from various sources, resulting in inconsistent tagging. For instance, a file might have a title set to "Unknown" or a date far in the future. Fixing these issues requires direct manipulation of the container's header rather than altering the visual or audio streams. This approach is fast because it avoids the CPU-intensive process of transcoding.

Inspecting Current Metadata

Before making changes, you should verify what metadata currently exists in your file. This diagnostic step helps you identify which tags are problematic and which ones are already correct. You can inspect the metadata by running ffmpeg with the -i input flag and directing the output to a text file or the console.

ffmpeg -i movie.mp4 -hide_banner 2>&1 | grep -i metadata

This command will list all available metadata fields. Look for keys like title, artist, date, or comment. If you see values that are clearly wrong, such as a random string of characters or an empty field, you know exactly what needs to be corrected. Note that different containers support different sets of metadata keys. MP4 and MKV formats handle tags slightly differently, so always check the documentation for your specific file type if standard keys do not work.

Correcting Specific Metadata Fields

Once you have identified the incorrect fields, you can overwrite them using the -metadata option. This flag allows you to specify a single key-value pair. To fix multiple fields, you simply add multiple -metadata flags to your command line. It is crucial to remember that this operation copies the streams, so no quality loss occurs.

ffmpeg -i input.mp4 -c copy -metadata title="My Correct Title" -metadata artist="Author Name" output.mp4

In this example, -c copy tells ffmpeg to copy the audio and video streams directly without re-encoding them. This makes the operation nearly instantaneous. The -metadata title=... part updates the title tag, while -metadata artist=... updates the artist tag. You can replace "Author Name" with any relevant string. If you want to remove a specific tag entirely, you can set its value to an empty string, although some players may still show the key with no value.

Handling Dates and Custom Tags

Dates often cause confusion because they can be stored in various formats. Some players expect ISO 8601 format (YYYY-MM-DD), while others accept Unix timestamps. If you are struggling with date formatting, consider looking into how other tools handle temporal data. For more details on preserving date information during conversions, see Preventing FFmpeg Scale Command from Removing 'Date Taken' Metadata. This resource explains why certain operations might strip existing date tags and how to prevent that loss.

Custom tags are also useful for organizing libraries. You can add arbitrary keys like -metadata genre="Action" or -metadata description="A brief summary". These tags are widely supported by modern media centers. However, avoid using special characters that might break parsing in older software. Stick to alphanumeric characters and simple punctuation for maximum compatibility.

Batch Processing Multiple Files

If you have hundreds of files with incorrect metadata, manual entry is inefficient. You can create a script to automate the process. A simple Bash loop can iterate through all MP4 files in a directory and apply a correction pattern. While each file still requires individual processing, the script handles the repetition.

for f in *.mp4; do ffmpeg -i "$f" -c copy -metadata title="Fixed Title" "${f%.mp4}_fixed.mp4"; done

This script takes each .mp4 file, runs the ffmpeg command, and saves the output with a "_fixed" suffix. Be careful to back up your original files before running batch scripts, as overwriting errors can lead to data loss. Always test on a single file first to ensure the command behaves as expected.

Common Pitfalls and Solutions

Sometimes, metadata does not update even after running the command. This usually happens if the media player caches old information. Restarting the player or clearing its cache often resolves this. Another issue is permission errors. Ensure you have write access to the directory where the output file is being saved. If you encounter issues with displaying the video in HTML after modification, check your encoding settings, as seen in Troubleshooting: Unable to Display FFMPEG-Created Video in HTML.

Additionally, some proprietary containers may restrict metadata editing. In such cases, converting the file to a more open format like MP4 or MKV might be necessary before applying fixes. Always verify the final result by playing the file in your preferred media player and checking the properties panel.

Frequently Asked Questions

Does fixing metadata change the video quality?

No, using the -c copy flag ensures that the video and audio streams are copied directly without re-encoding. This means there is zero loss in quality or resolution. Only the container's header information is modified, which is a lightweight operation.

How do I remove all metadata from a video file?

You can remove all metadata by creating a new file with no metadata flags specified and then deleting the old one. Alternatively, some versions of ffmpeg support -map_metadata 0:s:0 to map only specific streams, but completely stripping metadata often requires using specialized tools like AtomicParsley for MP4s or mkvtoolnix for MKVs after the initial copy.

Why does my media player still show the old title?

Most media players cache metadata to improve loading times. After updating the file, you need to restart the application or clear its library cache. For example, in Plex, you can go to Settings > Library and click "Scan Library Files" to force it to re-read the metadata from the disk.

Can I edit metadata for MKV files the same way?

Yes, the -metadata flag works similarly for Matroska (MKV) files. However, MKV supports a much wider range of custom tags than MP4. You can use keys like TITLE, ARTIST, and GENRE just like in MP4, but you can also add unique identifiers or cover art directly into the container using additional flags.

What if the metadata key name is unknown?

If you do not know the exact key name used by the file, run the inspection command listed earlier. The output will show all current keys. Use those exact key names in your -metadata commands. For example, if the inspection shows title=Old Title, you must use -metadata title=New Title to overwrite it.