Macos 从视频文件中提取音频并在OpenAL中播放

我希望能够从视频文件中提取音频并将其加载到OpenAL播放的缓冲区中，但我不知道从何开始

AVFoundation似乎是最简单的方法（与FFMPEG相比，不是吗？），但我找不到方法让缓冲区可以用OpenAL播放。我在MacOSX上使用，效果非常好

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我正在寻找有关它的建议、代码示例或教程

对于可能感兴趣的人，我是这样做的。它采用AVFoundation输入的所有格式

• 在AVAsset中加载我的文件（视频或音频）
• 获取音频曲目（AVAssetTrack）
• 在NSData中转换PCM中的曲目
• 添加WAV头（可选->ALBuffer需要不带头的数据）
• 向ALBuffer（from）提供数据

下面是构建PCM的代码（您会注意到我正在构建2个缓冲区，因为我需要反转音频文件）

和WAV标题，如果需要：

// ---- Creates the WAV data header and returns it
//
- (NSMutableData *) wavHeaderWithDataLength:(NSUInteger)length channels:(int)channels bitDepth:(int)bitDepth sampleRate:(long)sampleRate byteRate:(long)byteRate
{
// ---- The WAV header is 44 bytes long
//
long totalAudioLen = length;
long totalDataLen = totalAudioLen + 44;

// ---- The WAV header
//
Byte *header = (Byte*)malloc(44);
header[0] = 'R';
header[1] = 'I';
header[2] = 'F';
header[3] = 'F';
header[4] = (Byte) (totalDataLen & 0xff);
header[5] = (Byte) ((totalDataLen >> 8) & 0xff);
header[6] = (Byte) ((totalDataLen >> 16) & 0xff);
header[7] = (Byte) ((totalDataLen >> 24) & 0xff);
header[8] = 'W';
header[9] = 'A';
header[10] = 'V';
header[11] = 'E';
header[12] = 'f';
header[13] = 'm';
header[14] = 't';
header[15] = ' ';
header[16] = bitDepth; // 16;  // 4 bytes: size of 'fmt ' chunk
header[17] = 0;
header[18] = 0;
header[19] = 0;
header[20] = 1;  // format = 1
header[21] = 0;
header[22] = (Byte) channels;
header[23] = 0;
header[24] = (Byte) (sampleRate & 0xff);
header[25] = (Byte) ((sampleRate >> 8) & 0xff);
header[26] = (Byte) ((sampleRate >> 16) & 0xff);
header[27] = (Byte) ((sampleRate >> 24) & 0xff);
header[28] = (Byte) (byteRate & 0xff);
header[29] = (Byte) ((byteRate >> 8) & 0xff);
header[30] = (Byte) ((byteRate >> 16) & 0xff);
header[31] = (Byte) ((byteRate >> 24) & 0xff);
header[32] = (Byte) (2 * 8 / 8);  // block align
header[33] = 0;
header[34] = bitDepth; // 16;  // bits per sample
header[35] = 0;
header[36] = 'd';
header[37] = 'a';
header[38] = 't';
header[39] = 'a';
header[40] = (Byte) (totalAudioLen & 0xff);
header[41] = (Byte) ((totalAudioLen >> 8) & 0xff);
header[42] = (Byte) ((totalAudioLen >> 16) & 0xff);
header[43] = (Byte) ((totalAudioLen >> 24) & 0xff);

// ---- The header NSData
//
NSMutableData *headerData = [NSMutableData dataWithBytes:header length:44];

free(header);

return headerData;

}

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希望它能对别人有用

您对处理哪类文件感兴趣？就MP4？可能是AVI、WMV或其他？能够读取所有文件将是最好的…这是大量的工作，因为所有类型都是唯一的。

// ---- Creates the WAV data header and returns it
//
- (NSMutableData *) wavHeaderWithDataLength:(NSUInteger)length channels:(int)channels bitDepth:(int)bitDepth sampleRate:(long)sampleRate byteRate:(long)byteRate
{
// ---- The WAV header is 44 bytes long
//
long totalAudioLen = length;
long totalDataLen = totalAudioLen + 44;

// ---- The WAV header
//
Byte *header = (Byte*)malloc(44);
header[0] = 'R';
header[1] = 'I';
header[2] = 'F';
header[3] = 'F';
header[4] = (Byte) (totalDataLen & 0xff);
header[5] = (Byte) ((totalDataLen >> 8) & 0xff);
header[6] = (Byte) ((totalDataLen >> 16) & 0xff);
header[7] = (Byte) ((totalDataLen >> 24) & 0xff);
header[8] = 'W';
header[9] = 'A';
header[10] = 'V';
header[11] = 'E';
header[12] = 'f';
header[13] = 'm';
header[14] = 't';
header[15] = ' ';
header[16] = bitDepth; // 16;  // 4 bytes: size of 'fmt ' chunk
header[17] = 0;
header[18] = 0;
header[19] = 0;
header[20] = 1;  // format = 1
header[21] = 0;
header[22] = (Byte) channels;
header[23] = 0;
header[24] = (Byte) (sampleRate & 0xff);
header[25] = (Byte) ((sampleRate >> 8) & 0xff);
header[26] = (Byte) ((sampleRate >> 16) & 0xff);
header[27] = (Byte) ((sampleRate >> 24) & 0xff);
header[28] = (Byte) (byteRate & 0xff);
header[29] = (Byte) ((byteRate >> 8) & 0xff);
header[30] = (Byte) ((byteRate >> 16) & 0xff);
header[31] = (Byte) ((byteRate >> 24) & 0xff);
header[32] = (Byte) (2 * 8 / 8);  // block align
header[33] = 0;
header[34] = bitDepth; // 16;  // bits per sample
header[35] = 0;
header[36] = 'd';
header[37] = 'a';
header[38] = 't';
header[39] = 'a';
header[40] = (Byte) (totalAudioLen & 0xff);
header[41] = (Byte) ((totalAudioLen >> 8) & 0xff);
header[42] = (Byte) ((totalAudioLen >> 16) & 0xff);
header[43] = (Byte) ((totalAudioLen >> 24) & 0xff);

// ---- The header NSData
//
NSMutableData *headerData = [NSMutableData dataWithBytes:header length:44];

free(header);

return headerData;

}