How do meta data/tags work

[Gustavo_Fring]

If you don't want to read the main thread (it tells you where I'm coming from), heres the main question I need to ask:
"So the major thing I need to know is can I add my own custom textarea (or at least a text field with at least 100 characters? data to the metadata of audio/video/pdf/image files. I have future projects that will require me to do this with other filetypes too which don't use metadata, is there way to attach metadata to these files?

^^Now that I think of it, I'm being a bit silly, I can just create a .txt file for each of the multimedia files and give it an identical name to the video/image/track/whatever. I think I just answered my own question, but I'll go ahead and post this anyway because it contains useful programming info that can be used in conjunction with multimedia editing and cataloging. When I make the bash script, I'll post it here so others don't have to waste their time making, what looks like lt'll be a handy tool.

I'm a programmer, but pretty new to the multimedia field sp excuse me if I ask some silly questions. As far as I'm aware, various types of files including images, audio, video, even pdf documents have a metadata/tag feature which lets you attach data to the files. A lot of it is simply Artist names, Albums, Year etc. but I think theres an extra comments field where you can add your own info. Obviously that comments field would give you great power because you can add your own data to it, and code it in such a way that your scripts can read it.

I'm a linux user and know how to bash script, if I can find a way to add my own data section, then I can use bash scripts to organise my media files for me (i.e. I want to organise my videos, images, and music collections, but they are all stored in subdirectories so I will make a script that will alter metadata based on what subdirectory the files are in, then when every fille has metadata, I will scan all the files, make an XML entry (or whatever way I organise the files) for each file then I can setup a nice category based search and display system. So square 1 is I need to know if I can add my own custom tag to various multimedia files (as well as PDFs), then need to how to go about editing them. How to edit them all in batch, I know how to do that with a bash script (might use some PHP with it too since its more practical for data mining than pure bash) , what I don't know how to do is actually edit the metadata. It seems to be different for each type of video file, for example a video encoding with matroska needs one tool to edit the data, then to edit AVI files, I'll need another tool. Thats not really an issue, I'll just make the script edit each file type properly.

So the major thing I need to know is can I add my own custom textarea (or at least a text field with at least 100 characters?

[El Heggunte]

Here goes my suggestion, start by studying the source-code of MediaInfo --- after all, you'd better learn how to READ the various types of metadata, before learning how to WRITE them ^.^;

However, you have to be warned, the task won't be easy as you seem to believe The various media formats support different sets of metadata, and some are "more comprehensive" than others. Also, before studying the source-code of the several applications capable of writing metadata, you should get yourself familiar with a decent hexadecimal editor

[Gustavo_Fring]

What I had in mind was writing a shell script which uses command line editors, not writing my own editors. Bash scriptings easy enough when you know the syntax. It has pretty horrible syntax though, so getting familiar with it takes time. Thats one of the upsides of switching to linux, you end up learning how to use the terminal, and that means you end up learning a fully functioning programming language.

[poisondeathray]

The problem is varied specs between the various formats. You can't just insert the data anywhere without corrupting the files (especially video formats). And I don't think many of them have a field that will allow 100 characters . Each one has it's own specification, and not all formats have documentation available or open

Besides mediainfo, have a look at exiftool which can read/write to many formats and containers
http://www.sno.phy.queensu.ca/~phil/exiftool/

Have a look at some of the ffmpeg metadata handling
http://wiki.multimedia.cx/index.php?title=FFmpeg_Metadata

You're basically going to have to figure out which types you're likely going to use, figure out what tools are available already, which tools you'd have to write from the specs. It's not as easy as writing a bash script because many of the tools don't exist, many of the formats don't have the metadata entries or are very limited in terms of metadata capabilities, and/or many of the specs are not publically available . Many formats were developed eons ago without the foresight that metadata might actually be handy and were never revised

That text file approach looks hell of a lot easier to me.

Good luck