I am attempting to write a program in C++ that will need to display metadata from a MKV file and extract streams from the file.
I looked at libmatroska and found it difficult to use because it is very low level. There are also no examples on usage apart from mkvtoolnix making it difficult to use due to having to bring in most of mkvinfo and mkvextract. libmediainfo covers most of what I need although it would be nice to be more flexible if possible.
In addition, I have found no simple way of extracting the video stream without using mkvextract to write it to a temporary file.
Any advice would be appreciated
Related
I've seen a lot of examples of i/o with text files I'm just wondering if you can do the same with other file types like mp3's, jpg's, zip files, etc..?
Will iostream and fstream work for all of these or do I need another library? Do I need a new sdk?
It's all binary data so I'd think it would be that simple. But I've been unpleasently surprised before.
Could I convert all files to text or binary?
It depend on what you mean by "work"
You can think of those files as a book written in Greek.
If you want to just mess with binary representation (display text in Greek on screen) then yes, you can do that.
If you want to actually extract some info: edit video stream, remove voice from audio (actually understand what is written), then you would need to either parse file format yourself (learn Greek) or use some specialized library (hire a translator).
Either way, filestreams are suited to actually access those files data (and many libraries do use them under the hood)
You can work on binary streams by opening them with openmode binary :
ifstream ifs("mydata.mp3", ios_base::binary);
Then you read and write any binary content. However, if you need to generate or modify such content, play a video or display a piture, the you you need to know the inner details of the format you are using. This can be exremely complex, so a library would be recomended. And even with a library, advanced programming skills are required.
Examples of open source libraries: ffmpeg for usual audio/video format, portaudio for audio, CImg for image processing (in C++), libpng for png graphic format, lipjpeg for jpeg. Note that most libraries offer a C api.
Some OS also supports some native file types (example, windows bitmaps).
You can open these files using fstream, but the important thing to note is you must be intricately aware of what is contained within the file in order to process it.
If you just want to open it and spit out junk, then you can definitely just start at the first line of the file and exhaustively push all data into your console.
If you know what the file looks like on the inside, then you can process it just as you would any other file.
There may be specific libraries for processing specific files, but the fstream library will allow you to access any file you'd like.
All files are just bytes. There's nothing stopping you from reading/writing those bytes however you see fit.
The trick is doing something useful with those bytes. You could read the bytes from a .jpg file, for example, but you have to know what those bytes mean, and that's complicated. Usually it's best to use libraries written by people who know about the format in question, and let them deal with that complexity.
is it possible to do changes to image's matrix without using any library in c++? to load and display image as well?
Sure. Grab a copy of the specification for whatever image format you're interested and write the read/write functions yourself.
Note that to write display functionality without an external library you'll likely need to run your code in kernel mode to get to the frame buffer memory, but that can certainly be done.
Not that you'd necessarily want to do it that way...
Like any typical file, an image file is simply made up of bytes; there is nothing special about an image file.
In my opinion, the most difficult part of reading/writing image files without the use of a library is understanding the file format. Once you understand the format, all you need to do is define appropriate data structures and read the image data into them (for more advanced formats you may have to do some extra work e.g. decompression).
The simplest image format to work with would have to be PPM. It's a pretty bad format but it's nice and easy to read in and write back to a file.
http://netpbm.sourceforge.net/doc/ppm.html
Apart from that, bitmaps are also pretty simple to work with. Like Drew said, just download a copy of the specification and work from there.
As for displaying images, I think you're best off using a library or framework unless you want to see how it's done for the sake of learning.
So I see samples all around on saving into file. But I wonder if it is possible to save into char* or string instead of file - so to say keep it in memory?
There doesn't seem to be anything to facilitate this in boost itself. All I/O seems to be based on supplying filenames.
However, there seems to be an extension here called io_new that has streams based I/O.
See documentation here for an example (search for "Reading And Writing In-Memory Buffers").
I've seen a lot of games use something similar to a .DAT file or a specific file type that the game has for itself. I'm just beginning with C++ and DirectX and I was interested in keeping my information in something similar to a .DAT.
My initial conception was that it would hold information on the files you wanted to store within the .DAT file. Something similar to a .RAR file. Unfortunately, my googleing skills did not help me in finding the answers.
Right now I'm simply loading textures and sound files from a folder called Data.
EDIT: While I understand that .DAT is short for data, and I've found that a .DAT file generally contains any assortment of information, I'm still unsure about how to go about doing something as packing images and sound files into any type of file and being able to read them.
I'm not sure about using fstreams to achieve my task, however I will look into streams related to storing data and how to properly read from that data. Meanwhile if anyone has another answer to offer based on this new information, it would be appreciated.
EDIT: Thanks to the answers, I stumbled across a similar question on stackoverflow and felt I'd share it here. Combining resources into a single binary file
I don't think there is really such thing as .dat file format. It's short for "data," and different applications just put in some proprietary stuff in it and call it ".dat." You can read up on fstream classes to do file IO in C++. See Input/Output with files.
What you then do is make up your own file format. For example, first 4 byte is int that indicates the number of blocks in the .dat and for each block, you have 4 byte indicating the length of each block, 4 byte indicating the type of the block, the variable length data itself .. something like that.
DAT obviously stands for data, and there is no real or de facto standard on what that extension actually refers to. Your decisions on the best file formats should be based on technical considerations, not pointless attempts at security through obscurity.
Professional games use a technique where they put all the needed resources (models, textures, sounds, ai, config, etc) zipped/packed into a single file thus making it faster to manage, harder to change (some even make use of a virtual filing system from what's inside the data file). Now, for what's inside the file is different depending on the needs of the game and the data structures that you use.
If you're just starting into gamedev, i recommend you stick with keeping all you assets separate and don't bother too much about packing them into a single file.
Now if you really want to start using a packed format here's a good pointer:
Creating a PAK File Format
Here's a link which claims that .dat is a movie format, 'DAT' being short for Digital Audio Tape.
I'm not sure I believe the link, but I do remember something about a Microsoft supported format called DAT, from long ago, when I used an earlier version of Windows.
It makes more sense as a logical extension for a DATA file of some kind.
.dat, as others have said, is literally just a data file. In reality, the file extension means nothing other than association with a program. For example, I could make a word processor that saves all the documents with the .mp3 file extension. These files wouldn't be playable in any media software, but the software might try. File extensions are used to help programs know what types of files they can and cannot open--however those rules don't have to be followed.
Anyway, you can dump any sort of information to a file. Programmers/software writers will often choose .dat as the extension of that file because it has become the standard to signify 'this file just holds a ton of data' and that the data doesn't necessarily hold any standardized headers, footers, or formatting.
A dat file could really contain anything. It might be as simple as a zip archive with the extension changed, or it could be a completely custom file type. If you're just starting out, you probably don't want to write your own file format, although doing so can be fun and educational. If you want to encapsulate your data files into some kind of container, you should probably go with a zip, paq, or maybe tar.gz.
I want to decode JPEG files and obtain uncompressed decoded output in BMP/RGB format.I am using GNU/Linux, and C/C++.
I had a look at libjpeg, but there seemed not to be any good documentation available.
So my questions are:
Where is documentation on libjpeg?
Can you suggest other C-based jpeg-decompression libraries?
The documentation for libjpeg comes with the source-code. Since you haven't found it yet:
Download the source-code archive and open the file libjpeg.doc. It's a plain ASCII file, not a word document, so better open it in notepad or another ASCII editor.
There are some other .doc files as well. Most of them aren't that interesting though.
Unfortunately I cannot recommend any other library besides libjpeg. I tried a couple of alternatives, but Libjpeg always won. Is pretty easy to work with once you have the basics done. Also it's the most complete and most stable jpeg library out there.
MagickWand is the C API for ImageMagick:
http://imagemagick.org/script/magick-wand.php
I have not used it, but the documentation looks quite extensive.
You should check out Qt's QImage. It has a pretty easy interface that makes this task really easy. Setup is pretty simple for every platform.
If Qt is overkill, you can try Magick++ http://www.imagemagick.org/Magick++/. It supports similar operations and is also well suited for that sort of task. The last time I used it, I struggled a bit with dependencies for it on Windows, but don't recall much trouble on Linux.
For Magick++'s Image class, the function you probably want is getConstPixels.
I have code that you can copy ( or just use as a reference ) for loading a jpeg image using the libjpeg library.
You can browse the code here: http://code.google.com/p/kgui/source/browse/trunk/kguiimage.cpp
Just look for the function LoadJPGImage.
The code is setup to handle c++ binding of my DataHandle class to it for loading the image, that way the image can be a file or data already in memory or whatever.
A slightly out of the box solution is to acquire a copy of the netpbm tools, which transform images from pretty much any format to any other format via one of several very simple intermediate formats. They work well from the shell, and are most often used in pipes to read some arbitrary image, perform an operation on it, and write it out to some other format.
The pbm formats can be as simple as a plain ASCII header followed by the RGB data in ASCII or binary. They are intended to be simple enough to use without required a library to implement.
JPEG is supported in netpbm by read and write filters that are implemented on top of libjpeg.