Methods to Check if Original Audio/Video Has Been Modified

Ensuring the integrity of audio and video files is crucial in various professional and legal contexts. However, verifying the originality of these files can be complex. This article delves into the methods used to check if an audio or video file has been modified, including file properties and metadata, hash values, visual and audio analysis, digital signatures, forensic tools, and comparison with the original version.

File Properties and Metadata

One common method to check for modifications is by analyzing the filersquo;s metadata, which can provide important information about the filersquo;s origin and history. Tools such as MediaInfo and ExifTool are useful for examining metadata details like the creation date, modification date, codec information, and bitrate.

To compare the metadata with the original file, you can follow a step-by-step process:

Use MediaInfo or ExifTool to extract metadata from both the original and the potentially modified file. Compare key details such as the creation and modification dates, codec information, and bitrate. Red flags are indicated if these details do not match between the two files.

Hash Values

Another robust method is to generate and compare hash values. A hash value is a fixed-size string of characters that represents the contents of a file. Generating a SHA-256 hash for both the original and potentially modified file allows you to detect any alterations:

Generate a hash value for the original file using a command like sha256sum original_. After suspecting a file might have been modified, generate a hash for the modified file and compare it to the original hash. If the hashes do not match, it is highly probable that the file has been altered. Example of generating a SHA-256 hash

Visual and Audio Analysis

Inspecting the visual and audio elements of the file can also reveal modifications. For video, look for:

Consistency in quality: any abrupt changes or inconsistencies. Abrupt cuts or unusual transitions that may not be naturally occurring. Color, contrast, and lighting that do not match the original.

For audio, listen for:

Changes in audio quality. Unusual or unexpected sounds that may indicate edits. Noise levels or background sounds that differ from the original.

Digital Signatures

If the media comes from a reputable source, look for digital signatures or watermarks. These can indicate the authenticity and origin of the file. Many reputable media sources use digital signatures to ensure that the file has not been altered.

Forensic Tools

Specialized forensic tools can provide detailed analysis of the file. Here are some popular ones:

FFmpeg: For detailed analysis and manipulation. Avidemux: For video editing and checking codec information. Audacity: For audio analysis and visualization.

Using these tools, you can conduct a thorough examination of the file to identify any signs of modification.

Comparison with the Original Version

The most direct way to verify if a file has been modified is to compare it side by side with the original version. Play both files and note any discrepancies in content, timing, and technical aspects such as resolution and audio quality.

Check for Compression Artifacts

Modified files may exhibit different compression artifacts compared to the original. Using tools to analyze the compression levels can help detect if the file has been altered and how much has changed.

About the Evolution of Video Forensics

Before digital transformation, it was relatively easier to detect modifications in analog video and audio tapes. However, with advancements in digital technology, the process has become more challenging:

Analog tapes have a control track that, if edited, can be detected by special equipment. In contrast, digital video can be easily modified and it is difficult to tell if it has been altered without specialized tools. For analog audio, even slight differences in noise and equipment can be a telltale sign of tampering. Digital audio can be falsified in minutes using Digital Audio Workstations (DAWs) with the right utilities to change file timestamps, making it almost impossible to prove the originality of the file unless there is a third-party verification process in place.

For digital video, it is similarly challenging to prove the integrity of the footage. Techniques such as insert editing and time-stamp manipulation allow for seamless modifications, making it difficult for even advanced forensic analysis to detect tampering.

Therefore, ensuring the authenticity of audio and video files requires a combination of technical tools and expert knowledge. Utilizing hash values, meticulous metadata analysis, and specialized forensic tools are some of the methods that can help maintain the integrity of digital media.