音视频开发：音频fdk-aac编码

本文主要是介绍音视频开发：音频fdk-aac编码，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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");}