I am successfully using ExtAudioFileOpenUrl to open an audio file and play it.
One thing I have noticed is that the calculated audio length returned from ExtAudioFileGetProperty kExtAudioFileProperty_FileLengthFrames and an external editor e.g. Audacity and Wave Editor don't match. Interestingly the external editors don't quite agree with each other either.
Any idea why this would be?
After some investigating of various audio editors I've found that the discrepancy seems to be how they all read in mp3 files. If I used an mp3 file I found a variance in audio length between iOS, Audacity, Wave Editor and Twisted Wave.
If I converted the mp3 to caf however, iOS and all the editors agreed on the audio length.
One other interesting thing I found was that converting from mp3 to caf increased the reported audio length.
So the moral of the story is, if you are going to be capturing audio events at certain times convert to mp3 and then back again...
The decoded length of an MP3 file can vary depending on the decoder implementation, because of padding at the beginning of the decoded stream... see http://lame.sourceforge.net/tech-FAQ.txt for some discussion of this.
Related
I am making a simple application for iPhone, and I want to enter a short audio file on an object click. Which of .caf and .wav would be better?
I am building a simple application in Cocos2d in which balloons produce a pop sound when clicked. What are the memory issues with both sound versions?
If you do not need specific Core Audio Format features, then WAV has more universal support (and it would be my default choice for that reason).
Core Audio Format basically functions as a container for other audio file formats, including WAV. Core Audio Format has many great features, but it's not evident from the description that you need any of these.
In response to a deleted comment, which was moved to the question:
I can't speak for Cocos2d specifically, so I will write about the file formats in general: WAV does not use data compression. CAF may. If it is a short sound file, you probably don't want data compression (because it requires a good amount of processing to convert to LPCM for playback). If you play the pop often, then you will want to hold onto an uncompressed version of the audio data for easy processing. 1 second will require 44100 * 2 bytes at CD quality in memory (per channel).
For a short sound file such as a balloon pop, a 16 bit WAV file sounds ideal. In that sense, the memory difference should not be a deciding factor. If you have a lot of audio files, or long audio files to load into memory, then the situation changes. For now, I don't consider memory to be a problem in your case. Since CAF is a container, its uncompressed representation will be nearly identical (the difference will be a little more header data in the CAF).
A CAF file is a basically Core Audio Format. So it is well suited for the Apple frameworks. The best advantage of CAF over WAV is while recording when you can have files more than 4 GB and also in CAF you don't need to update the WAV header after each packet recording.
Anyway, I assume you don't need these features related to CAF. And as Justin said, I do believe that WAV will be the better option as you can have more support for WAV than the CAF format.
I have a sound file which requires to be split into smaller parts. Is there any way i can do it, dividing an audio file into small slices of sound as Music Cutter does.
I also need to check that sliced parts can be played individually.
Any help will be appreciated.
Thanks
Vikas Ojha
It depends on the specific format of the file - an mp3 file, no - a wav file, yes.
For an mp3 file you would have to decompress the audio from the file first (you could use an audioqueue ), then split the raw audio data how ever you please, then re-encode each slice as mp3. Apple has sample code for decoding and encoding mp3's.
This is still not going to enable you to accept any input file format, for that you would need other external libraries, such as ffmpeg, LAME, etc. you might have to build these yourself and they may have disagreeable licensing restrictions.
I was using AVAudioPlayer to play multiple audio clips back to back but there was always a small silence between tracks and then i came to know of Finch, a library which uses OpenAL to play audio. with this the silence problem seems to be solved theoretically but then i found that it doesn't play m4a or any other compressed formats.
Now i am looking for an uncompressed audio format which would have relatively less file size (though uncompressed means that all of them should have almost same size) and a method to convert, i am also googling on afconvert in a mean while.
CAF files work great for this. I've built an application that loops audio files, and I was impressed with the relatively small file size.
Check out this question for more info on converting to CAF.
I'm having a hard time trying to record something other than linear PCM on the iPhone :-(
The samples I've found (SDK's SpeakHere, Zdziarski's and Sadun's books and the one at trailsinthesand.com) all use linear PCM but I'd like a commonly used compressed format instead (no ima4 or whatever the name is...).
I just cannot figure out how to tweak the sample code to be used with, for example AAC, MP3 or AMR instead. Any suggestions and hints for how to do that are much appreciated!
(Btw, I do not think an MP3-encoder nor AMR-encoder are available due to licensing issues, but AAC does exist, or???)
Edit/Update: I stumbled upon the following text in Apple's "iPhone Application Programming Guide", 2009-01-06, page 137, section: Recording Audio:
"You can record audio in any of the formats listed in “Preferred Audio Formats in iPhone OS” (page 140)", and as preferred audio formats on page 140 are: "For compressed audio when playing one sound at a time, and when you don’t need to play audio simultaneously with the iPod application, use the AAC format packaged in a CAF or m4a file."
Thus, I interpret that as a clear indication that it is indeed, not only possible, but even preferable, to record audio in AAC format wrapped up in a m4a file, which is just what I want. But still, I am not able to achieve that?!
Thanks,
/John
Keep looking at those docs. In "Core Audio Essentials", the section "Core Audio Plug-ins: Audio Units and Codecs" notes that:
iPhone OS contains the recording
codecs listed in Table 2-5. As you can
see, neither MP3 nor AAC recording is
available. This is due to the high CPU
overhead, and consequent battery
drain, of these formats.
Table 2-5 lists several formats, but as the text notes does not include the ones you're looking for. If you want those formats you'll have to bring your own encoder.
It is possible in iPhone 3GS and iPod 2nd generation and above. They have a hardware enconder for AAC.
There is an Apple example project for this that does exactly what you want to do:
iPhoneExtAudioFileConvertTest
A tip for using faac to convert from iPhone-output linear pcm files to aac format:
I found by experimentation that you have to use the -X flag on the command-line version of faac (running on Mac OS X), which "swaps the input bytes." (I guess it changes the endian-ness.)
So, for example, if you audio recorded the file linear.pcm on your iPhone, you could then run:
faac -XP linear.pcm
on your mac to convert that into the aac file linear.aac.
I'm guessing this means you might be able to use faac within your app to do the conversion, if you wanted to, since it's a C library.
Also note that, technically, the files output by iPhone's audio services are usually CAF files, Core Audio Format, which is sort of a wrapper format around a bunch of possible encodings: Apple's docs on CAF. The above command line works fine for me even though linear.pcm starts with the caff header.
Have you tried Lame mp3 encoder? Or faac/faad AAC codecs? You can embed them in ffmpeg for even more audio codecs.
Why don't try TPAACAudioConverter written by the legendary Michael Tyson ?
TPAACAudioConverter is a simple Objective-C class that performs the
conversion of any audio file to an AAC-encoded m4a, asynchronously
with a delegate, or converts any audio provided by a data source class
(which provides for recording straight to AAC).
I am making an iPhone recording app that needs to submit the sound file as a .wav to an external server.
Starting from the SpeakHere example, I am able to record sound as a file, but only as .caf
Does anyone know how to record it as a wav instead? Or how to convert from .caf to .wav on the iphone? (The conversion must happen on the phone)
EDIT:
I'm wondering if anything can be done with using kAudioFileWAVEType instead of kAudioFileCAFType in AudioFileCreateWithURL
Yup, the key is kAudioFileWAVEType
AudioFileCreateWithURL (
audioFileURL,
kAudioFileWAVEType,
&audioFormat,
kAudioFileFlags_EraseFile,
&audioFileID
);
Changing to WAVE from CAF in the SpeakHere example causes the recording to be as wav. I also edit the same thing in the playback class, and changed the filename to be Recording.wav
Have a look at libsndfile. It is a well used (including by Audacity) C library for working with lots of file formats. It supports read and write of a variety of CAF and WAV formats.
The CAF File structure and WAV format are fairly similar. If the worst comes to the worst, converting shouldn't be too hard.
It would involve taking the Audio data chunk, and copying as is into the WAV file, and using the information in the Audio Description Chunk to add an equivalent fmt subchunk for the WAV file. It is fairly simple byte copying.
However, be aware (as Eric pointed out) there are licensing issues, see: Can the Libsndfile library be used on the iPhone iOS?