Thinking about metadata removal with FFmpeg
Learn how to think about processing video and audio with FFmpeg, its limits, and rechecking after processing.
FFmpeg is a widely used tool for audio and video conversion, re-encoding, and metadata processing.
In the context of anonymity, it can be a candidate for regenerating video or audio before publication and reducing unnecessary metadata.
However, using FFmpeg does not automatically make a file safe.
Even if you remove metadata, voices, background sounds, text in the video, faces, reflections, and the time of publication remain.
This article organizes how to think when using FFmpeg and what to check after metadata removal.
What is FFmpeg?
FFmpeg is a project used for audio and video conversion and processing.
On the official site, you can check project information, documentation, and download information.
URL : https://ffmpeg.org/
It is used for video and audio format conversion, re-encoding, audio extraction, metadata processing, and similar tasks.
The reason to introduce it for anonymity is that it can process files locally.
You can process files on your own device without uploading them to an external conversion site.
What FFmpeg can handle
FFmpeg can process audio and video containers and streams.
However, it does not judge every piece of information related to anonymity.
| What it can handle | What it cannot handle |
|---|---|
| Re-encoding | Judging the meaning inside video |
| Changing container information | Detecting signs, reflections, faces, and text |
| Removing or extracting audio | Judging voice identification risk |
| Processing metadata | Removing publication times or communication logs |
| Format conversion | Separating accounts or cloud history |
FFmpeg is a powerful processing tool.
The anonymity judgment still has to be made by a person.
Metadata removal and re-encoding have different purposes
With FFmpeg, you may combine processing that reduces metadata with processing that re-encodes video or audio.
However, these two things do not mean the same thing.
| Process | Purpose | Caution |
|---|---|---|
| Metadata removal | Reduce titles, creation information, tags, and similar data | Recheck the information you wanted to remove and any newly attached information |
| Re-encoding | Recreate video or audio | New encoding information may be attached |
| Audio removal | Remove voices and ambient sound | Information inside the video remains |
| Clipping | Keep only the needed part | Backgrounds and sound remain even in the clipped section |
| Format conversion | Change to another format | Content risks remain even if the format changes |
You cannot say "it is safe because it was re-encoded."
After re-encoding, check both metadata and content.
What to check before processing
Before processing with FFmpeg, check the original file.
| Check | Reason |
|---|---|
| Copy the original file | Do not mix the original and the publication version |
| Check metadata | Understand what you want to remove |
| Check the video | Look at backgrounds, reflections, text, and faces |
| Check the audio | Listen for voices, conversations, and ambient sound |
| Look at the filename | Check whether dates, places, or names remain |
If you do not know what is in the file before processing, you cannot judge what disappeared after processing.
Check metadata with ExifTool or a similar tool, regenerate with FFmpeg if needed, and check again.
ExifTool official site:
URL : https://exiftool.org/
Recheck after re-encoding
After re-encoding with FFmpeg, always check again.
Re-encoding may reduce old metadata, but new encoding information or creation times may also be attached.
| Check | Reason |
|---|---|
| Metadata | Whether old or new information remains |
| Video | Whether backgrounds or text remain after processing |
| Audio | Whether muting or replacement worked correctly |
| Filename | Whether a name containing original information remains |
| Playback check | Whether there is damage or unintended content |
"Processed" and "became safe" are different.
You can make a publication judgment only after checking the processing result.
Whether to remove audio
For video anonymity, whether to keep audio is important.
Voices, conversations, ambient sound, and announcements become strong clues.
| Audio state | Judgment |
|---|---|
| Your own voice is included | Consider voice alteration, removal, or not publishing |
| Nearby conversations are included | Be careful because this can involve other people |
| Station or store sounds are included | The location may be inferred |
| Notification sounds are included | The app or device environment may be revealed |
| Unnecessary audio | It may be acceptable to remove it |
Even if you remove audio, information visible from the video remains.
Check video and audio separately.
Avoid mixing up processed files
Video processing increases the number of files: original files, in-progress files, and files for publication.
If you mix them up here, you may accidentally publish the original file as-is.
| File | Handling |
|---|---|
| Original file | Store as the original and do not publish it |
| Working file | Manage it as a file in the middle of processing |
| Publication file | Use only a file whose metadata and content have been checked |
| Check results | Do not leave them in a real-name environment more than necessary |
| Unneeded files | Do not casually leave them in cloud sync |
Pay attention to filenames too.
A name such as home_near_station_original.mov leaks information even if metadata is removed.
Give files for publication names that are not too closely related to the content.
Why not use external conversion sites
Video and audio conversion sites are convenient.
However, if you upload a file where anonymity matters to an external site, the file, source IP address, time, and browser information are handed to that site.
For high-risk files, prioritize local processing.
Even with local processing, consider device and storage-location safety separately.
If you work on a workplace device, school device, shared PC, or cloud sync folder, other traces may remain.
Cases FFmpeg alone cannot solve
In cases like the following, processing with FFmpeg alone is not enough.
- Many faces or name tags appear in the video
- Names or places are mentioned many times in the audio
- The shooting location is easy to identify from the background
- Internal materials or screen notifications are visible
- The publication time itself indicates participation or behavior
In these cases, you need judgments such as not publishing, recreating the content, using still images, explaining in text, or waiting, rather than just re-encoding.
In anonymity work, separate problems that tools can process from problems that can only be solved by a publication judgment.
Where to check the processed video
Pay attention to the environment where you check the processed video.
If you upload it for checking to a cloud or video service where you are logged in with a real-name account, the account and file become connected at that point.
Check locally as much as possible.
Even when you need to check with an external service, use it only after understanding what is handed to the service side.
Summary
FFmpeg is a powerful tool used for audio and video conversion and re-encoding.
For anonymity, it helps process video and audio locally and reduce unnecessary metadata and audio.
However, FFmpeg does not automatically judge anonymity.
Even if you remove metadata, backgrounds, reflections, text, faces, voices, ambient sound, and the time of publication remain in the video.
Check before processing, recheck after processing, and finally judge whether the content is acceptable to publish.
Related tools
Wayback Machine
An external resource related to this article. Open it only when it fits your situation and threat model.
Why it is listed: It can help with the article topic, but it is outside Anonymity Sense and should be checked before use.
URL : https://web.archive.org/
ExifTool
An external resource related to this article. Open it only when it fits your situation and threat model.
Why it is listed: It can help with the article topic, but it is outside Anonymity Sense and should be checked before use.
URL : https://exiftool.org/
MAT2
An external resource related to this article. Open it only when it fits your situation and threat model.
Why it is listed: It can help with the article topic, but it is outside Anonymity Sense and should be checked before use.
FFmpeg
An external resource related to this article. Open it only when it fits your situation and threat model.
Why it is listed: It can help with the article topic, but it is outside Anonymity Sense and should be checked before use.
URL : https://ffmpeg.org/