#Hex reader hex fiend mp4#
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To stay inside nal units look for hex 67, 68 or 00 00 01 as these sequences can denote the beginning of a new nal unit.

Corrupting large regions of data will inevitably cross over structure boundaries and destroy important information regarding the type of nal unit or slice.

As mentioned previously the mdat is comprised of chunks, as chunks and the nal units contained within them have structure itвЂ™s best to corrupt small portions of data in various spots rather than large swaths.

Copying and pasting hex within nal units is probably the best way to corrupt H.264 video data as youвЂ™ll be shuffling valid data around rather than adding outright gibberish.

The mdat atom will also contain raw audio data so if the audio becomes distorted during playback we know weвЂ™ve gone too far, or started too early, in the mdat atom.

While not required, most data in the mdat will be in sequence so if we want to corrupt a specific portion of the video we can estimate the offset of the data for that portion is in the mdat based on its time.

It doesnвЂ™t take much corruption to add bizarre distortion to a video, even corrupting as little as 10% of a file, a couple of bytes here and there, has the potential to send playback into a wild frenzy.

Making backup copies after every successful change will avoid heartaches when, not if, a misstep renders the video unplayable. Once weвЂ™ve identified the boundaries of mdat atom we can begin to copy and paste, replace or edit portions of the raw hex data (or the text ASCII data, either will work) of the video and check the result along the way by attempting to play the video. Using this method we can identify both the start and the end of the mdat atom, and in turn where we can corrupt only the mdat atomвЂ™s contents and have a fair chance of the video still being playable. The mdat atom, in all cases, will either continue to the end of the file or it will be followed by another atom identified by a 4-character string such as the moov atom does in the above example. WhatвЂ™s important to note though is that the file is visibly more structured after the mdat atom, this is how we can identify where the mdat atom ends.

Here we can see that the mdat atom is followed by the moov atom (and an mvhd atom after that), this is not always the case as the order of the atoms can be different. With this information weВ can easily find the end of the mdat atom by scrolling through it (or up from the bottom of the file) to see where the data starts to look random as illustrated in the image below.

#Hex reader hex fiend mp4#

Notice that the contents of the mdat atom seem quite random when viewed in a hex editor, in contrast the contents of the other atoms in MP4 and MOV files are very structured. Finding the mdat atom can be done by searching the file for the string вЂњmdatвЂќ as seen in the above image. For the purposes of this tutorial we wonвЂ™t delve that deep. The data contained within the mdat atom is comprised of chunks, which are comprised of nal units, which are comprised of slices. The atom which contains the raw frame and audio data can be identified by itвЂ™s atom type string, which in this case is mdat (short for media data). The MP4 and MOV (Quicktime) formats utilize a similar structure, the file is broken down into atoms or blocks of data. We know that weвЂ™re looking at an MP4 or MOV file when we see the text ftypqt starting on the fifth byte of the file as illustrated in the example below. Editing the file using hex rather than text allows greater flexibility since weвЂ™re no longer restricted to text characters (which are each represented by two hex digits).

Hex editors allow us to view and edit the bytes of a file using hexadecimal. If you donвЂ™t have a hex editor installed there are some freeware options listed at the bottom of this post. Get started by making a copy of your MOV or MP4 and open the copy in a hex editor - never edit the original file.

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If a video doesnвЂ™t set off any copyright claims you can download it from the YouTube Video Manager in MP4 format. If the video you want to destroy is not in MP4 or MOV format already an easy way to convert it is to upload it to YouTube, let them convert it, and then download the result.

This tutorial will focus on glitching the popular MP4 and MOV formatsВ containing video compressed with the H.264В standard. Since video formats contain audio and timing information in addition to visual information corrupting the wrong section of a video file can quickly render the file unplayable rather than delightfully distorted. This is owing to the fact that video formats are substantially more complex than image formats. Glitching videos with data corruption can be a tricky process.