c ++音频转换（mp3 - > ogg）问题

Question

I was wondering if anyone knew how to convert an mp3 audio file to an ogg audio file. I know there are programs you can buy online, but I would rather just have my own little app that allowed me to convert as many files I wanted.

Answer 1

It's realtive simple. I wouldn't use the Windows Media Format SDK. Simply because of the fact that it's overkill for the job.

You need a MP3 decoder and a OGG encoder and a little bit of glue code around that (opening files, setting up the codecs, piping raw audio data around ect.)

For the MP3 decoder I suggest that you take a look at the liblame library or use this decoding lib http://www.codeproject.com/KB/audio-video/madlldlib.aspx as a starting point.

For OGG there aren't many choices. You need libogg and libvorbis. Easy as that. The example codes that come with the libs show you how to do the encoding.

Good luck.

Answer 2

It's a bad idea. To quote from the Vorbis FAQ

You can convert any audio format to Ogg Vorbis. However, converting from one lossy format, like MP3, to another lossy format, like Vorbis, is generally a bad idea. Both MP3 and Vorbis encoders achieve high compression ratios by throwing away parts of the audio waveform that you probably won't hear. However, the MP3 and Vorbis codecs are very different, so they each will throw away different parts of the audio, although there certainly is some overlap. Converting a MP3 to Vorbis involves decoding the MP3 file back to an uncompressed format, like WAV, and recompressing it using the Ogg Vorbis encoder. The decoded MP3 will be missing the parts of the original audio that the MP3 encoder chose to discard. The Ogg Vorbis encoder will then discard other audio components when it compresses the data. At best, the result will be an Ogg file that sounds the same as your original MP3, but it is most likely that the resulting file will sound worse than your original MP3. In no case will you get a file that sounds better than the original MP3.

Since many music players can play both MP3 and Ogg files, there is no reason that you should have to switch all of your files to one format or the other. If you like Ogg Vorbis, then we would encourage you to use it when you encode from original, lossless audio sources (like CDs). When encoding from originals, you will find that you can make Ogg files that are smaller or of better quality (or both) than your MP3s.

(If you must absolutely must convert from MP3 to Ogg, there are several conversion scripts available on Freshmeat .)

http://www.vorbis.com/faq/#transcode

And, for the sake of accuracy, from the same FAQ:

Ogg Ogg is the name of Xiph.org's container format for audio, video, and metadata.

Vorbis Vorbis is the name of a specific audio compression scheme that's designed to be contained in Ogg. Note that other formats are capable of being embedded in Ogg such as FLAC and Speex.

I imagine it's theoretically possible to embed MP3 in Ogg, though I'm not sure why anyone would want to. FLAC is a lossless audio codec. Speex is a very lossy audio codec optimised for encoding speech. Vorbis is a general-use lossy audio codec. "Ogg audio" is, therefore, a bit of a misnomer. Ogg Vorbis is the proper term for what I imagine you mean.

All that said, if you still want to convert from MP3 to Ogg Vorbis, you could (a) try the Freshmeat link above, (b) look at the other answers, or (c) look at FFmpeg. FFmpeg is a general-purpose library for converting lots of video and audio codecs and formats. It can do a lot of clever stuff. I have heard that its default Vorbis encoder is poor quality, but it can be configured to use libvorbis instead of its inbuilt Vorbis encoder. (That last sentence may be out of date now. I don't know.)

Note that FFmpeg will be using LAME and libvorbis, just as you already are. It won't do anything new for you that way. It just gives you the option to do all sorts of other conversions too.

Answer 3

You will need to decode mp3 then encode into ogg.

One possibility is to use liblame for mp3 decoding and libogg/libvorbis for encoding into ogg. Or just use the command line versions of those.

But I wouldn't say converting from one lossy format to another is a great idea.

Answer 4

Foobar2000 ( http://www.foobar2000.org/ ) is free and makes it quite easy to convert between file formats. It would take only a few clicks to convert from MP3 to OGG.

Keep in mind that moving from a lossy format to a lossy format will reduce the quality of the audio more than moving from a lossless format (FLAC, CD Audio, Apple Lossless Codec) to a lossy format (MP3, OGG, M4A). If you have access to the lossless source audio use that to convert it instead.

Answer 5

You can certainly do this in C++ with the Windows Media Format SDK .

I have only used WMFSDK9 myself. It contains a sample called UncompAVIToWMV, which may get you started. From the Readme:

It shows how to merge samples for audio and video streams from several AVI files and either merge these into similar streams or create a new stream based on the source stream profile. It also shows how to create an arbitrary stream, do multipass encoding and add SMPTE time codes.