How do I combine hundreds of binary files to a single output file in c++?

Question

I have a folder filled with hundreds of .aac files, and I'm trying to "pack" them into one file in the most efficient way that I can.

I have tried the following, but only end up with a file that's only a few bytes long or audio that sounds warbled and distorted heavily.

// Now we want to get all of the files in the folder and then repack them into an aac file as fast as possible
void Repacker(string FileName)
{
    string data;
    boost::filesystem::path p = "./tmp/";
    boost::filesystem::ofstream aacwriter;
    aacwriter.open("./" + FileName + ".aac", ios::app);

    boost::filesystem::ifstream aacReader;
    boost::filesystem::directory_iterator it{ p };
    cout << "Repacking File!" << endl;
    while (it != boost::filesystem::directory_iterator{}) {
        aacReader.open(*it, std::ios::in | ios::binary);
        cout << "Writing " << *it << endl;
        aacReader >> data;
        ++it;
        aacwriter << data;
        aacReader.close();
    }
    aacwriter.close();
}

I have looked at the following questions to try and help solve this issue

Merging two files together

Merge multiple txt files into one

How do I read an entire file into a std::string in C++?

Read whole ASCII file into C++ std::string

Merging Two Files Into One

However unfortunately, none of these answer my question.

They all either have to do with text files, or functions that don't deal with hundreds of files at once.

I am trying to write Binary data, not text. The audio is either all warbled or the file is only a few bytes long.

If there's a memory efficent method to do this, please let me know. I am using C++ 20 and boost. Thank you.

Answer 1

These files have an internal structure: header, blocks/frames, etc. and the simple presence of multiple headers within the concatenated file will mess up the expected result.

Take a look at the AAC file format structure, you'll see that it's not so simple.

Your best try should be to use FFMPEG, since it has a feature to concatenate media files without being forced to reencode data. It's a bit complex because FFMPEG's command line is quite complex and not always extremely intuitive, but it should works as long as all AAC files uses the same encoding and characteristics. Otherwise, you'll need to re-encode them - but it can be done automatically, too. Check this web research to get some base informations.

Otherwise, you may use the base libraries used by FFMPEG, for example libavcodec (available at ffmpeg.org), Fraunhofer FDK AAC, etc. but you'll have way, way more work to do and, finally, you'll do exactly what FFMPEG already do, since it relies on these libraries. Other AAC libraries won't be really easier to use.

Obviously, you can also "embed" FFMPEG within your application, call tools like ffprobe to analyze files and call ffmpeg executable automatically, as a child process.

CAUTION: Take a GREAT care about licensing if you plan to distribute your program. FFMPEG licensing is really not simple, most of the time it's distributed as sources to avoid vicious cases.