Develop Reference

Convert PCM to MP3/OGG

I need to convert a continuous stream of PCM, or encoded audio (ADPCM, uLaw, Opus), into MP3/OGG format so that it can be streamed to a browser (using html's audio tag). I have the "stream-mp3/ogg-using-audio-tag" part working, now I need to develop the conversion layer.
I have two questions:
How can I convert PCM into MP3/OGG using NAudio and/or some other C# library/framework? I assume there is a code snippet or two in the NAudio demo app that may be doing this, but I haven't been able to find it.
Do I have to convert the encoded data (ADPCM, uLaw, OPUS) into PCM (which I can) before I convert it into MP3/OGG, or can the MP3/OGG 'containers' accept the encoded data?
NOTE: I understand there my be licensing issues with MP3 so we are open to using OGG.
Thanks.

<Shameless Plug>
I wrote an addon for NAudio that uses libmp3lame from the LAME Encoder suite to handle MP3 encoding. It's on NuGet as NAudio.Lame, and the source is on GitHub.
</Shameless Plug>
Sadly the licensing issues remain if you are planning to use this for anything other than personal use. LAME itself is licensed under the LGPL, but the patents it implements still require licencing from Frauenhofer/Thompson according to the LAME Wikipedia entry. If you're planning to produce something for others this can get expensive.
The Vorbis compressor is unencumbered by patents and such, so it's a reasonable alternative. At some point I plan to do a similar wrapper to the OGG/Vorbis format. In the meantime, a quick Google Search turns up the Ogg Vorbis Interop Library which might be useful to you.
And yes, you will need PCM as an intermediate format in pretty much any conversion. NAudio gives you the tools to get PCM from a wide variety of audio formats.

To answer your first question, to create MP3 or OGG you need an encoder. NAudio does not include an MP3 or an OGG encoder. All it does is give you ways to access encoders that are already installed on your computer (such as ACM or Media Foundation Transforms). However, with both MP3 and OGG you'll find that the easiest way is to find an unmanaged DLL or a command line utility and access that from .NET. The article I wrote which you linked to above includes a brief explanation of how you can use LAME.exe with stdin and stdout to convert PCM to MP3 on the fly.
As for your second question, the answer is yes. Whenever you transcode, you first decode to PCM, then re-encode in the target codec. I think theoretically you can put audio encoded in any format into an OGG container, but in practice, audio in an OGG container is usually encoded with Vorbis. FLAC and OPUS may be options, but once again you'd need to find an application or library that can write the OGG container format for you, as I'm not aware of any fully managed OGG writers.

1) PCM to OGG
string fileName = #"e:\Down\male.wav";
Sox.Convert(#"sox.exe", fileName, fileName + ".ogg");
2) PCM to MP3
static void AnyToMp3(string fileName)
{
DsReader dr = new DsReader(fileName);
IntPtr formatPcm = dr.ReadFormat();
byte[] dataPcm = dr.ReadData();
dr.Close();
IntPtr formatMp3 = AudioCompressionManager.GetCompatibleFormat(formatPcm,
AudioCompressionManager.MpegLayer3FormatTag);
byte[] dataMp3 = AudioCompressionManager.Convert(formatPcm, formatMp3, dataPcm, false);
Mp3Writer mw = new Mp3Writer(File.Create(fileName + ".mp3"));
mw.WriteData(dataMp3);
mw.Close();
}

Conversion from avi to wmv

I would like to make an avi to wmv convertor on my own. For this, my understanding is I'd study the internal structure of an avi file and extract frame by frame and put in the way wmv encodes the frames. I would like to draw suggestions for learning the pattern of wmv. Is there any online documentation for a layman.

Hi Windows SDK is your best friend:
Learn Windows: Audio and Video Development
Microsoft Windows
Software Development Kit
Edit:
find more info about WMV here: http://en.wikipedia.org/wiki/Windows_Media_Video

Here you can find the WMV/ASF specifications:
Advanced Systems Format (ASF) Specification

How to convert AMR sound stream to PCM uncompressed stream in .NET

I need to convert an AMR (Adaptive Multi-Rate) audio file recorded in a phone (as a Stream object) to a PCM uncompressed wav audio Stream so it can be processed afterwards for speech recognition. The Speech Recognition doesn't like the AMR format. This is going to be a server application using the Microsoft Speech Platform. I am not sure about using the ffdshow or similar libraries in a .
Right now I am researching NAudio and DirectShowNet to see if they can help me accomplish this but was hoping someone can point in the right direction.

After a lot of searching for a solution for this, I am going to use ffmpeg. It provides the AMR-NB (NB=Narrow Band) decoder. There are a lot of c# wrappers for ffmpeg around; most of them abandoned efforts and one that is up to date but is not free. Just running ffmpeg with the basic parameters provides what I need, plus it is really fast.
I don't like the idea of calling an external process to do the conversion, plus I need to save the AMR stream as a file so it can be converted to a wav file but I believe I can make it work efficiently.

Audio Conversion C#

What is the best way to convert various audio formats to PCM?
For example: mp3, evrc, ogg vox.
Is there a library out there that will allow me to implement this relatively easily?
EDIT:
I guess my initial question wasn't really what I needed. Most of the libs I have found are file converters. What I need is a block converter, where I pass in a 1Kb block of vox data and it returns its converted PCM block. Of course I’ll have to tell the converter what type of data it is and various pieces of codec information.
The solution I am going for is to save and VOIP formats into a common wav format and to play that conformed file in real time. I thought there should be an easy way to do this because all audio is eventually turned into PCM before it is outputted anyways.

You can use NAudio to pass blocks of compressed audio into any ACM codecs you have installed on your machine. You do need to know how to create the appropriate WAVEFORMAT structure to describe the compressed audio type correctly though.

Check out AVBlocks SDK for .NET. It supports several audio formats, and audio transforms like Multi-channel audio to Stereo audio, resampling and bitrate conversion.

Try modified code from http://alvas.net/alvas.audio,tips.aspx#tip91
static void AnyToWav(string fileName)
{
DsReader dr = new DsReader(fileName);
IntPtr formatPcm = dr.ReadFormat();
byte[] dataPcm = dr.ReadData();
dr.Close();
WaveWriter ww = new WaveWriter(File.Create(fileName + ".wav"), AudioCompressionManager.FormatBytes(formatPcm));
ww.WriteData(formatPcm);
ww.Close();
}

Don't know any lib that does it all but we do mp3->wav using madxlib.
It's free but I suggest paying the $10 for the sdk as it comes with documentation and examples.

There is a c# tutorial on youtube that might be helpful to you. It shows how to use a specific audio library called alvas.audio that really does some neat things with audio. I found the video to be very educational. The audio library is completely written in c#. Watch the video for more details: http://www.youtube.com/watch?v=2DIQECXFPeU

Video Conversion to WMV

A project I am currently working on at work requires the ability to convert videos from other formats to the WMV format. We need to be able to convert virtually any video format that is commonly used to a WMV format. I am looking for a solution allot like On2's flix engine converts other video types to .flv videos. I am aware of the encoder that windows offers, but it has a very limited list of video types that it can convert from. Please let me know if you have any suggestions or opinions, or recommendation of software I can use to do this. I need to be able to do the conversions in batch and I need to be able to do them programmatically with C#.

Have you had a look at ffmpeg?
It seems to be at the core of many open source video conversion utilities, so I imagine you could use it in the scenario you describe.

SUPER, the name is really covering the load!

Well, first you have to be able to decode the file format. You need to set this up with directshow, which is very hard to work with. You can take a look at the mediaportal project for a directshow file player written in C#. Instead of using the video renderer at the end of the directshow graph, you would reencode the video and audio and mux them into a .wmv file. This is a very involved project to get right. You essentially have to mimic a player's ability to play any format and handle failure.

I've been very satisfied using Quick Media Converter.