I have an ogg vorbis file and I have to do two operations with it:
Cutting a part of a file from one position to another
Merging another file with existing one
How can I do these two operations in C#?
You can do this with libzplay http://libzplay.sourceforge.net/
The steps needed to do what is being asked about:
OpenFile
Seek
SetWaveOutFile(this supports .ogg exporting as well as other
formats)
StartPlayback
StopPlayback(at time needed)
Everything is extremely well documented on the linked site for multiple languages, including c#.
This answer is for all the other people that spent hours searching and weren't helped by the previous answers. This isn't a very efficient solution to the problem here, but while searching this question came up many times, and this might be helpful to others. :)
I'd look into the c documentation for libogg, and figure out how to do this with c. And then write almost the same code in C# using a wrapper over libogg.
I've created a low level wrapper over libogg and libvorbis using the interop assistant:
https://github.com/CodesInChaos/Xiph/blob/master/LowLevel.cs
That project also contains some higher level constructs, but I don't think they'll be useful for what you're doing.
BTW if the stream IDs between the files differ, you can simply append a file to another creating a valid file that plays both streams in sequence.
You probably need to read the input files packet wise using the decoding API, and then write the combined data out packet wise. Possibly replacing the stream ID and granulepos in between.
StreamID is an integer that identifies substreams in an ogg file. To append multiple such substreams you can simply ensure that they have a different ID and then write the data.
Splitting is a bit more annoying, since granulepos is a codec dependent timestamp, and I don't remember how it is defined for vorbis. Another problem here is that you can't simply split in the middle of a packet without reencoding.
Related
In .NET, I need a way to compare two files. I thought of a class, which represents a diff:
public enum DiffEntryState
{
New,
Removed,
Changed
}
public class DiffEntry
{
public byte[] Bytes;
public long FileOffset;
public DiffEntryState State = BackupByteEntryState.Changed;
}
The names should be pretty self-explanatory. I thought of adding a State to each entry, so that I can distinguish between the cases were the first file is larger than the second or vice versa.
I'm wondering, if there is a common and fast way to retrieve the byte-by-byte differences of two files. I would simply create a stream for each file and compare chunks of these streams until one ends. Is there a better way, or does the Framework have a built-in solution? Keep in mind that I need the differences itself, not only the feedback that there ARE differences.
//Edit:
After sleeping a night over the problem, I guess I'm taking the wrong approach here. The whole tool is a backup solution, which will be able to save only the changed bytes and thus reduce the overall necessary space for the backup. Instead of saving a compressed 14 MB file each time, only 200k or less will be saved.
But, after thinking about the problem, I realized that it wouldn't be enough to save only the differences byte-by-byte. Take a Text for example:
"This is a string."
"This was a string."
As a matter of fact, the only change here is "is" to "was". But my approach would assume that the changed content is now "was a string". If this happens at the beginning of a huge file, well, this approach is useless.
Obviously, I need a way to index a file and detect all moved, copied or changed blocks in comparison to the original file.
Phew...
Take a look at Diff.NET,could be helpful .
For general case binary differencing, look at A Linear Time, Constant Space Differencing Algorithm by Randal C. Burns and Darrell D. E. Long. Also, Randal Burns' master's thesis, Differential Compression: A Generalized Solution For Binary Files, goes into more detail and provides pseudo-code for the algorithm.
You might also get some useful ideas from About Remote Differential Compression and from Optimizing File Replication over Limited-Bandwidth Networks using Remote Differential Compression
For text file differencing, I recommend starting with An O(ND) Difference Algorithm and Its Variations by Eugene W. Myers. This algorithm can be used to diff any two sequences. To compare two text files, generate sequences of hash codes (e.g., by calling string.GetHashCode()) for each line in each file. Then run those sequences (e.g., IList) through Myers' algorithm to find the shortest edit script (i.e., inserts and deletes) that will convert the first sequence into the second.
I hope this helps. I'm the author of Diff.Net, and it uses Burns' algorithm for binary differencing and Myers' algorithm for text differencing. The source code for Diff.Net's libraries (Menees.Diffs and Menees.Diffs.Controls) are available under the Apache License, Version 2.0, and the references above should help you implement your own solution without having to start from scratch.
There is no built-in functionality.
So you have to compare the files byte by byte or use a library that does this for you.
In Silverlight one does not have access to the entire .NET Library and therefore I am considering the best way to get the functionality I would have courtesy of System.IO.Packaging.
I have multiple text files and I want to combine them into a single archive. Compression is not important but could wind up being valuable.
By instinct I would select an obscure characters as BOF/EOF tokens and then use a single stream to generate the multiple files, marking off BOF/EOF as a single file. I'd probably come up with a format to retrieve the original file name after the BOF as well.
But before I operate on a poor man's instinctive approach, is there a canonical approach to this? Or anyone who has done this before with some words of advice based on experience?
SharpZipLib works on the compact framework, there is no reason it won't work in SilverLight.
As for licensing (From their page):
"In plain English this means you can
use this library in commercial
closed-source applications."
Is there a SDK that can be used in managed code to shred files securely?
EDIT: This is the only link i could find in google that helps me
EDIT: Either SDK or some kind of COM based component.
This code from codeproject may be a good starting point.
Eraser has been around for years, you could call out to it by using System.Diagnostics.Process, or at least review the algorithm there.
Take a look at Windows.WinAny.Helper at the CodePlex. It has SecureDelete extension which allows you to shredd files with different algorithms like Gutmann, DoD-7, DoD-3, Random or Quick.
Technology has changed in the past few years so when I happened to see this answer (why wasn't an answer accepted again?) I wanted to provide an update for others with similar questions.
Please note that shredding is very much filesystem and media dependent. Attempting to "shred" a file on a log based filesystem or a filesystem stored on smart (write leveling) flash isn't going to get you very far. You would have to, at a minimum, write enough data to complete fill the device to hope that the old data might be overwritten one time.
More likely you would have to write several smaller files and when you get FS full, delete one and then keep writing a new one, to ensure that all reserved space has been overwritten as well. Then you will probably be fairly safe. Probably.
I say probably because the storage media/FS could decide that a block was failing (or used too much relatively) and map it away substituting some other part of the disk instead. This is a per-block thing of course, so any much larger file is unlikely to be reconstructed.
What is the best way to search a large binary file for a certain substring in C#?
To provide some specifics, I'm trying to extract the DWARF information from an executable, so I only care about certain parts of the binary file (namely the sections starting with the strings .debug_info, .debug_abbrev, etc.)
I don't see anything obvious in Stream, FileStream, or BinaryReader, so it looks like I'll have to read chunks in and search through the data for the strings myself.
Is there a better way?
There's nothing built into .NET that will do the search for you, so you're going to need to read in the file chunk by chunk and scan for what you want to find.
You can speed up the search in two ways.
Firstly, use bufferred IO and transfer large chunks at a time - don't read byte by byte, read 64KB, 256KB or 1MB chunks.
Secondly, don't do a linear scan for the piece you want - check out the Boyer-Moore (wikipedia link) algorithm for string searches - you can apply this to searching for the DWARF information you want.
I think you'll have to do it yourself, BinaryReader was not designed for searching for text in a binary file. However, you should be mindful of the text encoding you use when searching.
There must be a DWARF C library you could compile and use interop with? I did some searching and found this. If a library from there could be compiled into a DLL on Windows (I assume you're using Windows), then you could use System.Runtime.InteropServices to interact with the DLL and extract your information from there.
Perhaps?
Does anyone have, or know of, a binary patch generation algorithm implementation in C#?
Basically, compare two files (designated old and new), and produce a patch file that can be used to upgrade the old file to have the same contents as the new file.
The implementation would have to be relatively fast, and work with huge files. It should exhibit O(n) or O(logn) runtimes.
My own algorithms tend to either be lousy (fast but produce huge patches) or slow (produce small patches but have O(n^2) runtime).
Any advice, or pointers for implementation would be nice.
Specifically, the implementation will be used to keep servers in sync for various large datafiles that we have one master server for. When the master server datafiles change, we need to update several off-site servers as well.
The most naive algorithm I have made, which only works for files that can be kept in memory, is as follows:
Grab the first four bytes from the old file, call this the key
Add those bytes to a dictionary, where key -> position, where position is the position where I grabbed those 4 bytes, 0 to begin with
Skip the first of these four bytes, grab another 4 (3 overlap, 1 one), and add to the dictionary the same way
Repeat steps 1-3 for all 4-byte blocks in the old file
From the start of the new file, grab 4 bytes, and attempt to look it up in the dictionary
If found, find the longest match if there are several, by comparing bytes from the two files
Encode a reference to that location in the old file, and skip the matched block in the new file
If not found, encode 1 byte from the new file, and skip it
Repeat steps 5-8 for the rest of the new file
This is somewhat like compression, without windowing, so it will use a lot of memory. It is, however, fairly fast, and produces quite small patches, as long as I try to make the codes output minimal.
A more memory-efficient algorithm uses windowing, but produces much bigger patch files.
There are more nuances to the above algorithm that I skipped in this post, but I can post more details if necessary. I do, however, feel that I need a different algorithm altogether, so improving on the above algorithm is probably not going to get me far enough.
Edit #1: Here is a more detailed description of the above algorithm.
First, combine the two files, so that you have one big file. Remember the cut-point between the two files.
Secondly, do that grab 4 bytes and add their position to the dictionary step for everything in the whole file.
Thirdly, from where the new file starts, do the loop with attempting to locate an existing combination of 4 bytes, and find the longest match. Make sure we only consider positions from the old file, or from earlier in the new file than we're currently at. This ensures that we can reuse material in both the old and the new file during patch application.
Edit #2: Source code to the above algorithm
You might get a warning about the certificate having some problems. I don't know how to resolve that so for the time being just accept the certificate.
The source uses lots of other types from the rest of my library so that file isn't all it takes, but that's the algorithm implementation.
#lomaxx, I have tried to find a good documentation for the algorithm used in subversion, called xdelta, but unless you already know how the algorithm works, the documents I've found fail to tell me what I need to know.
Or perhaps I'm just dense... :)
I took a quick peek on the algorithm from that site you gave, and it is unfortunately not usable. A comment from the binary diff file says:
Finding an optimal set of differences requires quadratic time relative to the input size, so it becomes unusable very quickly.
My needs aren't optimal though, so I'm looking for a more practical solution.
Thanks for the answer though, added a bookmark to his utilities if I ever need them.
Edit #1: Note, I will look at his code to see if I can find some ideas, and I'll also send him an email later with questions, but I've read that book he references and though the solution is good for finding optimal solutions, it is impractical in use due to the time requirements.
Edit #2: I'll definitely hunt down the python xdelta implementation.
Sorry I couldn't be more help. I would definately keep looking at xdelta because I have used it a number of times to produce quality diffs on 600MB+ ISO files we have generated for distributing our products and it performs very well.
bsdiff was designed to create very small patches for binary files. As stated on its page, it requires max(17*n,9*n+m)+O(1) bytes of memory and runs in O((n+m) log n) time (where n is the size of the old file and m is the size of the new file).
The original implementation is in C, but a C# port is described here and available here.
Have you seen VCDiff? It is part of a Misc library that appears to be fairly active (last release r259, April 23rd 2008). I haven't used it, but thought it was worth mentioning.
It might be worth checking out what some of the other guys are doing in this space and not necessarily in the C# arena either.
This is a library written in c#
SVN also has a binary diff algorithm and I know there's an implementation in python although I couldn't find it with a quick search. They might give you some ideas on where to improve your own algorithm
If this is for installation or distribution, have you considered using the Windows Installer SDK? It has the ability to patch binary files.
http://msdn.microsoft.com/en-us/library/aa370578(VS.85).aspx
This is a rough guideline, but the following is for the rsync algorithm which can be used to create your binary patches.
http://rsync.samba.org/tech_report/tech_report.html