编码的大概流程见下图
1.获取编码器: avcodec_find_encoder_by_name("libfdk_aac")
2.检查PCM格式是否被编码器支持
3.创建编码上下文: AVCodecContext *ctx = avcodec_alloc_context3(codec)
4.给上下文设置参数
5.打开编码器: avcodec_open2
6.创建AVFrame: av_frame_alloc
7.创建AVPacket: av_packet_alloc
8.打开文件
9.读取数据，放入AVFrame
10.把AVFrame数据放入编码器: avcodec_send_frame
11.从编码器中获取编码好的数据并放入AVPacket: avcodec_receive_packet
12.写入文件
13.全部读完以后刷新缓冲区
14.释放资源
话不多说，上代码
#include <libavutil/samplefmt.h>
#include <libavcodec/avcodec.h>
typedef struct {
NSString *filePath;
int sampleRate;
enum AVSampleFormat sampleFmt;
int chLayout;
} AudioEncodeSpec;
//检查编码器是否支持当前采样格式
static int check_sample_fmt(const AVCodec *codec, enum AVSampleFormat sample_fmt) {
const enum AVSampleFormat *p = codec->sample_fmts;
while (*p != AV_SAMPLE_FMT_NONE) {
if (*p == sample_fmt)
return 1;
p++;
}
return 0;
}
//音频编码
static int encode(AVCodecContext *ctx,
AVFrame *frame,
AVPacket *pkt,
NSFileHandle *writeHandle) {
int ret = avcodec_send_frame(ctx, frame);
if (ret < 0) {
NSLog(@"avcodec_send_frame error");
return ret;
}
//不断从编码器取出编码后的数据
while (true) {
ret = avcodec_receive_packet(ctx, pkt);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
//继续读取数据
return 0;
} else if (ret < 0) {//其它
return ret;
}
[writeHandle seekToEndOfFile];
[writeHandle writeData:[NSData dataWithBytes:pkt->data length:pkt->size]];
//释放
av_packet_unref(pkt);
}
}
+ (void)aacEncode:(AudioEncodeSpec)spec outFilename:(NSString *)outFilename
{
//返回结果
int ret = 0;
//编码器
AVCodec *codec = avcodec_find_encoder_by_name("libfdk_aac");
if (!codec) {
NSLog(@"找不到编码器");
return;
}
//检查输入格式是否支持，fdk-aac只支持16位整数
if (!check_sample_fmt(codec, spec.sampleFmt)) {
NSLog(@"采样格式不支持");
return;
}
//编码上下文
AVCodecContext *ctx = avcodec_alloc_context3(codec);
if (!ctx) {
NSLog(@"编码上下文创建失败");
return;
}
//设置PCM参数
ctx->sample_rate = spec.sampleRate;
ctx->sample_fmt = spec.sampleFmt;
ctx->channel_layout = spec.chLayout;
//固定比特率
ctx->bit_rate = 44100;
//规格
ctx->profile = FF_PROFILE_AAC_HE;
//打开编码器
ret = avcodec_open2(ctx, codec, NULL);
if (ret < 0) {
NSLog(@"打开编码器失败");
avcodec_free_context(&ctx);
return;
}
//存放编码前的数据
AVFrame *frame = av_frame_alloc();
if (!frame) {
NSLog(@"av_frame_alloc error");
avcodec_free_context(&ctx);
return;
}
//frame缓冲区的样本帧数量
frame->nb_samples = ctx->frame_size;
//采样格式
frame->format = ctx->sample_fmt;
//声道布局
frame->channel_layout = ctx->channel_layout;
//创建缓冲区
ret = av_frame_get_buffer(frame, 0);
if (ret < 0) {
NSLog(@"av_frame_get_buffer error");
avcodec_free_context(&ctx);
av_frame_free(&frame);
return;
}
//存放编码后的数据
AVPacket *pkt = av_packet_alloc();
if (!pkt) {
NSLog(@"av_packet_alloc error");
avcodec_free_context(&ctx);
av_frame_free(&frame);
return;
}
//创建输出的文件
NSString *outFilePath = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES).lastObject stringByAppendingPathComponent:outFilename];
NSFileManager *writeManager = [NSFileManager defaultManager];
if ([writeManager fileExistsAtPath:outFilePath]) {
[writeManager removeItemAtPath:outFilePath error:nil];
}
[writeManager createFileAtPath:outFilePath contents:nil attributes:nil];
NSFileHandle *writeHandle = [NSFileHandle fileHandleForWritingAtPath:outFilePath];
//打开输入文件
NSFileHandle *readHandle = [NSFileHandle fileHandleForReadingAtPath:spec.filePath];
[readHandle seekToFileOffset:0];
NSData *readData = [readHandle readDataOfLength:frame->linesize[0]];
int len = (int)[readData length];
frame->data[0] = (uint8_t *)[readData bytes];
while (len > 0) {
//从文件中读取的数据，不足以填充frame缓冲区
if (len < frame->linesize[0]) {
int bytes = av_get_bytes_per_sample(frame->format);
int ch = av_get_channel_layout_nb_channels(frame->channel_layout);
//设置真正有效的样本帧数量
frame->nb_samples = ret / (bytes * ch);
}
if (encode(ctx, frame, pkt, writeHandle) < 0) {
break;
}
readData = [readHandle readDataOfLength:frame->linesize[0]];
frame->data[0] = (uint8_t *)[readData bytes];
len = (int)[readData length];
}
//刷新缓冲区
encode(ctx, NULL, pkt, writeHandle);
//释放资源
[readHandle closeFile];
[writeHandle closeFile];
av_frame_free(&frame);
av_packet_free(&pkt);
avcodec_free_context(&ctx);
NSLog(@"faac编码完成");
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