Getting the audio waveform data of media file using ffmpeg.exe in C#

2013-12-30 10:32:51 · Author: Wudi · Tagged with: C# & .NET, Audio Processing

Previously, I use the NAudio library to implement this function. It needs to extract the audio track of a media file to a separate WAV file to deal with. Even with the help of RAM disk, the processing speed is still very slow.

Yesterday, I searched again for the usable audio processing library in C#. But there is still no better choice. Finally, the popular cross-platform command line tools mencoder, ffmpeg and so on came into my head. The ffmpeg seems to work because it support stdout output.

At first, I tried to output the binary stream in WAV format to stdout. But I found that in this situation, ffmpeg will write a placeholder for size information in head, and seek back to rewrite it after the whole stream is outputed (source). When the output target is the stdout stream instead of a file, this rewriting operation will fail, which causes the obtained WAV stream to have wrong head information and cannot be used.

The reason that I use WAV format is just because it is the most familiar audio format that storing raw waveform data. But after read the documentation of ffmpeg, I found that it supports a great many formats. It can output integers or floats directly, without head information. At last I selected the little endian 32-bit float format.

The complete code is as follows:

using System.Diagnostics;
using System.IO;
 
// ...
 
static void Main(string[] args)
{
    // ...
    string path = @"E:\Media\test.mp4";
 
    Process proc = new Process();
    proc.StartInfo.FileName = @"E:\ffmpeg\ffmpeg.exe";
    proc.StartInfo.Arguments = "-i \"" + path + "\" -vn -ar 44100 -ac 1 -f f32le -";
    proc.StartInfo.CreateNoWindow = true;
    proc.StartInfo.UseShellExecute = false;
    proc.StartInfo.RedirectStandardOutput = true;
    proc.StartInfo.RedirectStandardError = true;
    proc.ErrorDataReceived += new DataReceivedEventHandler(proc_ErrorDataReceived);
    proc.Start();
    proc.BeginErrorReadLine();
    ProcessStream(proc.StandardOutput.BaseStream);
 
    proc.WaitForExit(10000); // 10s
    if (!proc.HasExited)
    {
        proc.Kill();
        Environment.Exit(1);
    }
    // ...
}
 
static void proc_ErrorDataReceived(object sender, DataReceivedEventArgs e)
{
    if (e.Data != null)
    {
        // Console.WriteLine(e.Data);
        // do nothing
    }
}
 
static void ProcessStream(Stream stream)
{
    int didread;
    int offset = 0;
    byte[] buffer = new byte[sizeof(Single) * (1024 + 1)];
 
    int length, residual_length;
 
    while ((didread = stream.Read(buffer, offset, sizeof(Single) * 1024)) != 0)
    {
        length = offset + didread;
        residual_length = length % sizeof(Single);
 
        if (residual_length == 0) {
            ProcessBuffer(buffer, length);
            offset = 0;
        } else {
            length -= residual_length;
            ProcessBuffer(buffer, length);
            Array.Copy(buffer, length, buffer, 0, residual_length);
            offset = residual_length;
        }
    }
}
 
static void ProcessBuffer(byte[] buffer, int length)
{
    int index = 0;
    float sample_value;
 
    while (index < length)
    {
        sample_value = BitConverter.ToSingle(buffer, index);
        index += sizeof(Single);
        // to deal with sample_value
    }
}
 
// ...

Current language: English · 其他语言: 中文 (简体)

3 Comments

gou9ping

Mon, 11 Apr 2016 15:28 +0800

你好！
请问下ffmpeg 如何计算出音频的分贝呢？

skygamer

Mon, 11 Dec 2017 18:26 +0800

Hello. I want to get waveform as stream for convert stream to image. I think your code what was i need. But i can't handle my image. I put a picturebox on my form. and want to show waveform on this picturebox.

can you help me please?

skygamer

Mon, 11 Dec 2017 19:14 +0800

how can i deal with sample_value for draw waveform on my picturebox? It's urgent. Please.