Bitstream
FFglitch is a multimedia bitstream editor. But what exactly does the word bitstream mean?
A bitstream is a stream of bits.
You didn’t see that one coming, did you? No, but seriously…
Multimedia files such as AVI, MOV, MKV, and MP4 (or any other kind of file, for that matter) are made up by a sequence of ones and zeros, which could also be called a sequence of bits, which could also be called a stream of bits, which could also be called a bitstream.
But… what is a bit?
Bit
I asked ChatGPT to define a bit for me, and this was the response:
A bit is the tiniest unit of information that can be processed by a computer, which is just a fancy way of saying that it’s the amount of time you can spend watching cat videos before realizing you have work to do.
Ha! Isn’t AI funny?
Anyways… a bit is the tiniest unit of information that can be processed by a computer. That bit is a number that is either a zero (0) or a one (1). Basically it just tells you that something is either on or off, and this something can be whatever you want.
For example:
| Bit | Meaning |
|---|---|
0 |
The lights are off |
1 |
The lights are on |
But it could also be using inverted logic, and therefore be:
| Bit | Meaning |
|---|---|
0 |
The lights are on |
1 |
The lights are off |
But one bit by itself is just one tiny unit of information. We’re going to need more bits to get more useful information.
For example, the ASCII standard can be used to represent characters in text, such as:
| Sequence | Meaning |
|---|---|
0100011 |
The number sign # (no, this is not a hashtag) |
0110111 |
The number 7 |
1000001 |
The uppercase letter A |
1100001 |
The lowercase letter a |
Note that the ASCII sequences above are all 7 bits long.
Byte
A byte is a sequence of eight (8) bits.
In UTF-8, the previous ASCII
sequences would be:
| Bit sequence | Byte (decimal) | Byte (hex) | Meaning |
|---|---|---|---|
00100011 |
35 |
0x23 |
The number sign # (no, this is still not a hashtag) |
00110111 |
55 |
0x37 |
The number 7 |
01000001 |
65 |
0x41 |
The uppercase letter A |
01100001 |
97 |
0x61 |
The lowercase letter a |
Bytestream
A bytestream is a stream of bytes.
We could also argue that a bytestream is a bitstream, since a byte is made up of bits. But normally we only use the expression bytestream when the sequence of information is clearly split across byte boundaries.
Usually the headers and the metadata in a multimedia file format are byte-oriented, and the encoded audio and video frames themselves are bit-oriented.
It is relatively easy to edit the bytestream of a file in a hex editor. It is much harder to edit a bitstream though, since the data is not aligned to byte boundaries, and adding/removing a single bit would have to change the values of all bytes following the edit.
And that’s what makes FFglitch so special, since it works on the bitstream level, and not only the bytestream level.