By comparing frames in both files and checking that the hex data is the same.Rather than focusing on the changed file hash, what’s actually important is proving that the wrapping process didn’t change the underlying image data or any visual information in the file. The rewrapped file has different binary data than the original and will have a different file hash. mp4 file, showing that we have in fact changed the 1s and 0s from the original file. But the file hash has changed in our new. When we look at our rewrapped file, all the characteristics look the same: frame rate, pixel format, and so on. mp4 output easily by selecting an MP4 output node, and selecting the Transcode Video option “Same as Input.” Using an iNPUT-ACE workflow, we can re-wrap the file to produce an. 264 file that we can’t double-click to launch in a standard player, but iNPUT-ACE can read the file and play it back correctly (Learn more about containers, codecs, and raw video here.) If we need to convert this file into a standard format, one solution is to give the file a container via a process called rewrapping. Viewing images in an uncompressed format is just as good as viewing the images in an original file (at least as far as the image data is concerned).įor example, we could have a. In other words, forensic video analysts care more about ensuring that evidentiary pictures don’t change during a conversion than the file itself not changing. That said, in video analysis, we should be more concerned with not changing the actual image data (visual information), and not as concerned with ensuring the binary data for the entire file. However, since proprietary video files often need to be converted, and this process results in a changed file hash, how can we reliably convert the video while ensuring and proving the authenticity of the results? Implications of Converting Video Filesįorensically speaking, when you alter the underlying data of a file by converting it, the file has been “changed”, and that terminology can have implications when testifying. This is important in forensic analysis, because if we can show that the file being presented to the court is the exact file that was recorded by the DVR (via identical file hash), we can then authenticate the video and not be overly concerned with questions of authenticity at trial. In other words, simply moving the location or changing those external details about the file doesn’t change the underlying binary data.Ĭonversely, if we change any bit of data-any single 1 or 0-the entire file hash will change.
For example, if a file is emailed to someone, then uploaded to Dropbox, then downloaded and onto a thumb drive, and opened on another computer years later, as long as the underlying 1s and 0s of the file haven’t changed, the exact same file hash will be maintained from the original file. If no 1s and 0s change in the video file, regardless of where the file is sent, what processes it goes through, what it is named, and so on, then the file hash will not change. If two videos have the same file hash, then they are the same file. A hash is a unique signature for each file, like a fingerprint. File HashĪnother important element in reading and validating video files is identifying the file’s file hash. Viewing this hex reader provides a wealth of information if you highlight a hex value of a piece of data, you can cross-reference with its binary 8-bit value, its integer value, its ASCII representation, and more. Using INPUT-ACE, it’s possible to quickly snap to the exact binary (or HEX) position of an exact frame of your video by selecting the File Metadata dropdown on the Interrogate tab and choosing Hex at Current Position. While the correct codec can interpret the images accurately, the wrong codec produces problems with playback. In order to play a file, video players identify a necessary codec, which acts like a language that reads the 0s and 1s of the binary video data, interpreting and getting meaning from the data in order to play it. Video files, like all computer files, are binary. In order to understand some of the pitfalls of the video conversion solution, it’s important to understand what underlies the video itself. Understanding the Underlying Data in Video Files