android 8k 8bit mono PCM
有个场景需要用 Android 手机采样 8k 8bit 单声道原始 PCM 流，但是 Android API 不支持 8bit，只能通过算法由 16bit 手动转换。找了一些转换方法，但都不灵光，大伙帮忙想点办法吧～
采样大致的样子：
private static final int SAMPLERATE = 8000;
private static final int DSAMPLERATE = 16000;
private static final int SOURCE = MediaRecorder.AudioSource.MIC;
private static final int CHANNEL = AudioFormat.CHANNEL_CONFIGURATION_MONO;
private static final int STREAM_TYPE = AudioManager.STREAM_MUSIC;
private static final int TRACK_MODE = AudioTrack.MODE_STREAM;
// 16bit 采样转换成 8bit，比特率会减半，故在采样时用两倍的采样率
int rate = (8 == bit) ? DSAMPLERATE : SAMPLERATE;
minSize = AudioRecord.getMinBufferSize(rate, CHANNEL, AudioFormat.ENCODING_PCM_16BIT);
if (minSize > 128) {
AudioRecord rec = new AudioRecord(SOURCE, rate, CHANNEL,
AudioFormat.ENCODING_PCM_16BIT, minSize);
rec.startRecording();
while (isRec) {
rec.read(data, 0, block);
// balabala
}
rec.stop();
rec.release();
}
转换调用：
for (int i = 0; i < out.length; i++) {
short origin = (short) (data[i * 2 + 1] << 8 | data[i * 2]);
out[i] = (byte) (origin >> 8 | 0x80);
}
播放：
AudioTrack track = new AudioTrack(STREAM_TYPE, SAMPLERATE, CHANNEL,
((16 == bit) ? AudioFormat.ENCODING_PCM_16BIT
: AudioFormat.ENCODING_PCM_8BIT), minSize, TRACK_MODE);
track.play();
while(...) {
track.write(data, offset, length);
}
track.stop();
track.release();
如果 bit 是 16，采样和播放都是没有问题的，换成 8 播放会是一片机械杂音，不知道肿么办鸟。可以确认的是，Android 采样的数据是小端的字节，所以让后面的字节在高位。
星野ましろ
9 years, 11 months ago