如何在 iPhone 上录制 AMR 音频格式?

问题描述

录音机不需要未压缩的线性 PCM 音频.压缩的 AMR 就可以了.为录制音频而构建的 iPhone 框架非常简单，但我发现的用于设置音频格式(来自 Apple)的唯一示例使用 LinearPCM.我已经尝试了各种其他的值组合，但似乎无法得到任何工作.

A voice recorder doesn't need uncompressed Linear PCM audio. Compressed AMR would do fine. The iPhone framework built for recording audio is simple enough, but the only examples I've found for setting up the audio format (which come from Apple) use LinearPCM. I've tried various other combinations of values, but can't seem to get anything to work.

有没有人有任何实际记录AMR的代码?

Does anybody have any code that actually records AMR?

AMR 格式是设置数据类型的选项之一，但其他选项(数据包大小、帧大小等)无论我设置为什么似乎都不匹配.

The AMR format is one of the options for setting the data type, but the other options (packet size, frame size, etc.) don't seem to match up no matter what I set them to.

这是我的 PCM 版本:

Here's what I have for the PCM version:

/*
 If we want to use AMR instead of PCM:
 AMR Format:
 Sampling Frequency: 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200-3400 Hz
 eight source codecs :  12.2, 1.2, 7.95, 7.40, 6.70, 5.90, 5.15, 4.75 kbit/s
 generated frame length: 244, 204,  159,  148,  134,  118,  103,   95 bits per frame
 */
format->mFormatID = kAudioFormatLinearPCM;
format->mSampleRate = 8000.0;    //8 kHz
format->mFramesPerPacket = 1;    //1 frame per packet
format->mChannelsPerFrame = 1;    //Mono
format->mBytesPerFrame = 2;        //8/bits per frame (round up)
format->mBytesPerPacket = 2;    //Same as bytes per frame
format->mBitsPerChannel = 16;    //16-bit audio
format->mReserved = 0;            //always 0
format->mFormatFlags = kLinearPCMFormatFlagIsBigEndian |
                       kLinearPCMFormatFlagIsSignedInteger |
                       kLinearPCMFormatFlagIsPacked;

推荐答案

AMR 编解码器不支持在 iPhone 上编码/录制，尽管它支持播放:这就是 kAudioFormatAMR 常量存在的原因.

AMR codec is NOT supported for encoding/recording on the iPhone, albeit it is supported for playback: this is the reason the kAudioFormatAMR constant exists.

官方 api 说支持的编码格式是:

Official api says that supported encoding formats are:

• ALAC(Apple Lossless)~> kAudioFormatAppleLossless
• iLBC(互联网低比特率编解码器，用于语音)~> kAudioFormatiLBC
• IMA/ADPCM (IMA4) ~> kAudioFormatAppleIMA4
• 线性 PCM ~> kAudioFormatLinearPCM
• μ-law ~> kAudioFormatULaw
• a-law ~> kAudioFormatALaw

• ALAC (Apple Lossless) ~> kAudioFormatAppleLossless
• iLBC (internet Low Bitrate Codec, for speech) ~> kAudioFormatiLBC
• IMA/ADPCM (IMA4) ~> kAudioFormatAppleIMA4
• linear PCM ~> kAudioFormatLinearPCM
• µ-law ~> kAudioFormatULaw
• a-law ~> kAudioFormatALaw

您可以尝试其中一种格式或使用开源 AMR 编码器作为 goldenmean 建议.

You may try one of these formats or use an open source AMR encoder as goldenmean suggests.

编辑:更新官方 api 链接

edit: Updated Official api link

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