I have a few questions about this after reading the iPhone documentation on it:
Does this take the audio being played and save it to a buffer so it can be written to a file?
If so does the audio being played have to be played using a playback audio queue or can it be played via a higher level class such as AVAudioPlayer.
Can anyone point me in the direction of some sample code or further help than the docs.
Thanks
Yes
Pretty sure you need to use a/the playback audio queue.
This Apple QA points to a file called aqrender.cpp which implements point 1.
Related
I've just started working on a project that requires me to do lots of audio related stuff on iOS.
This is the first time I'm working in the realm of audio, and have absolutely no idea how to go about it. So, I googled for documents, and was mostly relying on Apple docs. Firstly, I must mention that the documents are extremely confusing, and often, misleading.
Anyways, to test a recording, I used AVAudioSession and AVAudioRecorder. From what I understand, these are okay for simple recording and playback. So, here are a couple of questions I have regarding doing anything more complex:
If I wish to do any real-time processing with the audio, while recording is in progress, do I need to use Audio Queue services?
What other options do I have apart from Audio Queue Services?
What are Audio Units?
I actually got Apple's Audio Queue Services programming guide, and started writing an audio queue for recording. The "diagram" on their audio queue services guide (pg. 19 of the PDF) shows recording being done using an AAC codec. However, after some frustration and wasting a lot of time, I found out that AAC recording is not available on iOS - "Core Audio Essentials", section "Core Audio Plug-ins: Audio Units and Codecs".
Which brings me to my another two question:
What's a suitable format for recording, given Apple Lossless, iLBC, IMA/ADPCM, Linear PCM, uLaw/aLaw? Is there some chart somewhere that someone might be able to refer to?
Also, if MPEG4AAC (.m4a) recording is not available using an audio queue, how is it that I can record an MPEG4AAC (.m4a) using AVAudioRecorder?!
Super thanks a ton in advance for helping me out on this. I'll super appreciate any links, directions and/or words of wisdom.
Thanks again and cheers!
For your first question, Audio Queue services or using the RemoteIO Audio Unit are the appropriate APIs for real-time audio processing, with RemoteIO allowing lower and more deterministic latency, but with stricter real-time requirements than Audio Queues.
For creating aac recordings, one possibility is to record to raw linear PCM audio, then later use AV file services to convert buffered raw audio into your desired compressed format.
I am developing one application. In that I want to record the sounds and I want to play that recorded sound file. I know the frameworks for doing this. But how to develop programmatically by using that frameworks?
You can refer to this link:
I have implemented this code in one of my apps and it works completely fine.
How do I record audio on iPhone with AVAudioRecorder?
For Playing the sound you have option to use AVAudioRecorder.
Hope this helps.
The best way to do it - and I am talking from painful experience here - is with the RemoteIO audio unit. You can also do it with AudioQueue, but it has a higher latency, and the queue type approach becomes very problematic.
So, I think that they are really different tools for different jobs. Note that you won't play a sound file as such. You will play the contents of a buffer held in memory. As long as the buffer is not too large, this should not be an issue.
So, going with RemoteIO, you will find this blog and tutorial very useful. It includes code samples.
Using RemoteIO audio unit By MICHAEL TYSON
I'm trying to develop a metronome for iPhone. I've tried using an NSTimer and Apples SoundEngine.h to play a tick, but it doesn't seem to be very accurate. I've seen several forums that Auido Queue can be used to create a more precise metronome. I haven't used Audio Queue before, but I've looked at "Audio Queue Services Programming Guide" and SpeakHere sample code. Still I don't have a clue as to how to generate sound data on the fly (as opposed to reading from a file) and play it using Audio Queue. Can somebody help me? I'd love to see a code sample or at least some pseudo code describing the steps to do the timing and feed audio data from a short audio clip to the Queues.
Thanks
well, you looked at the wrong 'sample code' from apple... see this one!!!
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.
Can someone explain how we can use Audio Queue services to record sound from Microphone and play it live? Explain how we can achieve it. If possible give code snippets.
Use RemoteIO Audio Unit. This awesome code will get you on the right path.