Which format should I use?

The short answer: Use CAFF (uncompressed) for short sound effects and AIFF IMA4 (compressed) for music. This is also the recommendation from Apple.

• CAFF (Core Audio File Format) is, in a nutshell, the iPhone's native audio file format for uncompressed sounds.
• AIFF (Audio Interchange File Format) with IMA4 gets you about 4:1 compression on audio files. It is supported natively by the iPhone. One other advantage of this format is that it loops seamlessly - most other compressed audio files are problematic in this regard.

 

# creates sound.caf (little endian, 16 bit) afconvert -f caff -d LEI16 sound.wav  

# creates sound.caf (little endian, 16 bit, 22kHz) afconvert -f caff -d LEI16@22050 sound.wav  

# creates sound.caf (little endian, 16 bit, MONO) afconvert -f caff -d LEI16 -c 1 sound.wav  

# creates sound.aifc (IMA4 compression) afconvert -f AIFC -d ima4 sound.wav  

# creates sound.aifc (IMA4 compression, MONO) afconvert -f AIFC -d ima4 -c 1 sound.wav

若是要轉(zhuǎn)換一個(gè)文件夾內(nèi)的所有音頻文件，可創(chuàng)建如下的一個(gè)腳本：

#!/bin/bash 

for i in *.wav; do   

afconvert -f caff -d LEI16 $i 

done  

# move new files to project directory 

mv *.caf ~/my_project_path/sounds/

存儲(chǔ)該腳本文件名為 convert_sounds.sh，拷貝到要轉(zhuǎn)換的音頻文件夾內(nèi)，在終端執(zhí)行如下命令：

chmod u+x convert_sounds.sh    

./convert_sounds.sh

 

linear PCM在iphone上的采用的是 little-endian integer 16-bit，簡(jiǎn)稱 LEI16，而在mac上用的是 native-endian float 32-bit；

ios都采用caf格式音頻文件

采樣率使用 44,100Hz

比特率列表：

• 32kbit/s: AM Radio quality
• 48kbit/s: Common rate for long speech podcasts
• 64kbit/s: Common rate for normal-length speech podcasts
• 96kbit/s: FM Radio quality
• 128kbit/s: Most common bit rate for MP3 music
• 160kbit/s: Musicians or sensitive listeners prefer this from 128kbit/s
• 192kbit/s: Digital radio broadcasting quality
• 320kbit/s: Virtually indistinguishable from CDs
• 500kbit/s-1,411kbit/s: Lossless audio encoding such as linear PCM

afplay, afinfo,  afconvert(執(zhí)行 afconvert -hf可打印出能轉(zhuǎn)換的所有音頻格式 )

afconvert -d [out data format] -f [out file format] [in file] [out file] 例：

afconvert -d LEI16 -f caff input_file.xxx output_file.caf （使用linear PCM數(shù)據(jù)格式創(chuàng)建caf格式音頻,ios最常用的格式）

afconvert -d aac -f caff -b 32768 background-music-lei.caf test_32.caf （-b后跟比特率32768=32*1024，即32kbit/s）

 

錄制音效Audacity軟件： http://audacity.sourceforge.net/

該軟件保存的是 16-bit big-endian signed integer格式，所以最后還要轉(zhuǎn)換成 LEI16

 

播放音效，此種方式僅支持?jǐn)?shù)據(jù)格式為linear PCM和IMA4，文件格式為caf，aif和wav，長(zhǎng)度不超過30秒的音頻文件：

NSString *pewPewPath = [[NSBundle mainBundle] pathForResource:@"pew-pew-lei" ofType:@"caf"]; 

NSURL *pewPewURL = [NSURL fileURLWithPath:pewPewPath]; 

AudioServicesCreateSystemSoundID((CFURLRef)pewPewURL, &_pewPewSound); 

AudioServicesPlaySystemSound(_pewPewSound);

播放背景音樂，開始播放前會(huì)有一定的延遲：

NSError *error; 

_backgroundMusicPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:backgroundMusicURL error:&error]; 

[_backgroundMusicPlayer prepareToPlay]; 

[_backgroundMusicPlayer play];