I want to record the sound of my iPhone-App. So like someone is playing something on a iPhone instrument and after that you can hear it.
Is it possible without the micro?
Do you mean an App you build yourself? If yes, you could just save the rendered waveform (maybe encoded/compressed to save space) for later playback. (see: Extended Audio File Services, it can write the same AudioBufferList to a file that you would render to the RemoteAudio Unit when playing audio in your Instrument-App)
[Edit: removed comments on recording third-party app audio output ...]
With the AVFoundation you are currently using, you're always working on the level of the sound files. Your code never sees the actual audio signal. Thus, you can't 'grab' the audio signal that your app generates when it is used. Also, AVAudioPlayer does not provide any means of getting to the final signal. If you're using multiple instances of AVAudio player to play multiple sounds at the same time you also wouldn't be able to get at the mixed signal.
Alas, you probably need to use CoreAudio which is a much more low level interface.
I'd like to suggest an alternative approach: Instead of recording the audio output, why not record the sequence of actions together with their time which lead to the audio being played? Write this sequence of events to a file and read it back in to reproduce the 'performance' - it's a bit like your own MIDI sequencer :)
Related
I am writing an app that generates music. I am using OpenAL to: modify gain; modify pitch; mix audio; and play the resulting audio. I now need to record the audio as it is being played. I understand that OpenAL does not let you record the output audio. The other options I have found is to use audio units. However because I need to mix/pitch/gain the audio and record it, it seems I need to write all the audio processing so I can have access to the output buffer. Is this correct? Or is there a different iOS API I can use to do this. If not then is there a 3rd party solution already that lets me record the output (paid solutions are fine)?
You are correct.
Audio Units are the only iOS public API that allows an app to both process and then record audio.
Trying to record the OpenAL output may well be a violation of Apple's rules against using non-public APIs.
The alternative may be to completely rewrite the portions of OpenAL you need (there may be open source for some portions) running on top of the RemoteIO Audio Unit.
The best way to go is likely to be Core Audio, since it will give you as much flexibility as you need. Take a look into the Extended Audio File Services reference pages.
Using and extended audio file you should be able to set up a file format and audio stream buffer to send the final mixed output to, and then use the ExtAudioFileWrite() function to write the samples to the file.
I have a series of sounds that a user will play, rearrange, and edit etc. while using my app. When the user is finished, I want them to be able to save their work and record it to an mp3.
I don't want to play it through speakers and record it with the mic since that will result in low sound quality and interference. I cannot think of any ways of doing this that doesn't require extra hardware and/or a computer.
How can I do this using just their device?
Well, I would say it cant be done with AVFoundation.
My suggestion is to use Audio Units, and transform all your interactions to an audio graph. at some point you set a render notify on the RemoteIO so every time it renders sounds to the speakers you get a callback where you can write it down those frames/packets/data into a file.
I will probably suggest to use AAC(m4a) over MP3. I am not very fond of MP3, and to be honest as far as I know the sdk does not provide encoding to MP3, probably due to licensing issues. I could be wrong though. Check this sample code below, probably the best sample code you will ever find on Audio units on the web.
AudioGraph by Tom Zic
so I'm making an app and what I need to do is when for example someone starts talking I need to detect that there is a sound and then record it.
I found this tutorial http://mobileorchard.com/tutorial-detecting-when-a-user-blows-into-the-mic/ but it starts the recording on the beginning and then based on the recording it detects the sound.
Is there any other way to detect a sound without actually starting the recorder first? What I thought of would be having 2 recorders, one for detection and one for actually recording the sound. Another solution would be to edit (trim) the sound after it's recorded.
Are these approaches somehow standard or is there a better way to detect sound?
Thanks.
edit: if anyone ever reads this, I also found this http://bonkel.wordpress.com/2010/03/03/frequency-detection-using-fourier-transform/
If you don't mind getting a little dirty, you could go down to a lower level, to CoreAudio, and read data out of the input buffers until you see values exceeding your threshold, and start recording those input buffers, or triggering a high level recording call. You can similarly stop recording after a period of silence.
If you use CoreAudio, you have a lot of control over what you record. You could, pretty easily, filter out background noise, or add beeps to signify when the recording stopped due to silence, and even add markers to use later to match time to the recording.
CoreAudio does require you to do more work. You will have to read the microphone buffers on a timely basis and either save or discard the data pretty quickly in order not to drop any sound data. This isn't that hard, as the devices have plenty of CPU power to do that and other tasks at the same time - you just have to have a good grasp of CoreAudio.
There are plenty of Apple CoreAudio samples that can guide you. The WWDC 2010 and 2010 CoreAudio sessions are also a must-see.
You could use either the Audio Queue or the Core Audio (RemoteIO Audio Unit) API. Unless your app requires low latency, the Audio Queue API may be simpler to use.
You need to start the recording API to detect any sound, but you don't need to save everything you get from the recording callback to a file.
I'm currently working on a project where it is necessary to record sound being played by the iPhone. By this, I mean recording sound being played in the background like a sound clip or whatever, NOT using the built-in microphone.
Can this be done? I am currently experimenting with the AVAudioRecorder but this only captures sound with the built-in microphone.
Any help would be appreciated!
This is possible only when using only the Audio Unit RemoteIO API or only the Audio Queue API with uncompressed raw audio, and with no background audio mixed in. Then you have full access to the audio samples, and can queue them up to be saved in a file.
It is not possible to record sound output of the device itself using any of the other public audio APIs.
Just to elaborate on hotpaw2's answer, if you are responsible for generating the sound then you can retrieve it. But if you are not, you cannot. You only have any control over sounds in your process. yes, you can choose to stifle sounds coming from different processes. but you can't actually get the data for these sounds or process them in any way.
I am trying to create something similar like Piano app on the iPhone. When people tap a key, it play a piano note. Basically, there will have only 7 notes (C) at the moment. Each note is a .caf file and its length is 5 seconds.
I do not know if there is any way to save the song user played and export to mp3/caf format? The AVAudioRecord seems only record from the microphone input.
Many thanks
For such an app you probably don't want to record into an audio-file - instead record the note-presses and timings for a much more compact format and then play back the same as if the user was pressing the notes at the recorded times.
If you do want to be able to export an audio file format then you can write a simple mixer which adds together the individual samples from your source samples with the correct offsets and puts the results in your output audio buffer. You should probably also write a very simple compressor so that you keep the sample volume without any distortion caused by 'clipping'. This can be done by dividing down any summed sample above 95% of the maximum sample value. There may also be a way to use OpenAL to do this mixing for you and play back into an audio buffer.