音视频实战--自定义输入输出IO

avio_alloc_context函数

/**
* @projectName   07-05-decode_audio
* @brief         解码音频，主要的测试格式aac和mp3
* @author        Liao Qingfu
* @date          2020-01-16
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <libavutil/frame.h>
#include <libavutil/mem.h>#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>#define BUF_SIZE 20480static char* av_get_err(int errnum)
{static char err_buf[128] = {0};av_strerror(errnum, err_buf, 128);return err_buf;
}static void print_sample_format(const AVFrame *frame)
{printf("ar-samplerate: %uHz\n", frame->sample_rate);printf("ac-channel: %u\n", frame->channels);printf("f-format: %u\n", frame->format);// 格式需要注意，实际存储到本地文件时已经改成交错模式
}static int read_packet(void *opaque, uint8_t *buf, int buf_size)
{FILE *in_file = (FILE *)opaque;int read_size = fread(buf, 1, buf_size, in_file);printf("read_packet read_size:%d, buf_size:%d\n", read_size, buf_size);if(read_size <=0) {return AVERROR_EOF;     // 数据读取完毕}return read_size;
}static void decode(AVCodecContext *dec_ctx, AVPacket *packet, AVFrame *frame,FILE *outfile)
{int ret = 0;ret = avcodec_send_packet(dec_ctx, packet);if(ret == AVERROR(EAGAIN)) {printf("Receive_frame and send_packet both returned EAGAIN, which is an API violation.\n");} else if(ret < 0) {printf("Error submitting the packet to the decoder, err:%s\n",av_get_err(ret));return;}while (ret >= 0) {ret = avcodec_receive_frame(dec_ctx, frame);if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {return;} else if (ret < 0)  {printf("Error during decoding\n");exit(1);}if(!packet) {printf("get flush frame\n");}int data_size = av_get_bytes_per_sample(dec_ctx->sample_fmt);//        print_sample_format(frame);/**P表示Planar（平面），其数据格式排列方式为 :LLLLLLRRRRRRLLLLLLRRRRRRLLLLLLRRRRRRL...（每个LLLLLLRRRRRR为一个音频帧）而不带P的数据格式（即交错排列）排列方式为：LRLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRL...（每个LR为一个音频样本）播放范例：   ffplay -ar 48000 -ac 2 -f f32le believe.pcm并不是每一种都是这样的格式*/// 这里的写法不是通用，通用要调用重采样的函数去实现// 这里只是针对解码出来是planar格式的转换for(int i = 0; i < frame->nb_samples; i++) {for(int ch = 0; ch < dec_ctx->channels; ch++) {fwrite(frame->data[ch] + data_size *i, 1, data_size, outfile);}}}
}int main(int argc, char **argv)
{if(argc != 3) {printf("usage: %s <intput file> <out file>\n", argv[0]);return -1;}const char *in_file_name = argv[1];const char *out_file_name = argv[2];FILE *in_file = NULL;FILE *out_file = NULL;// 1. 打开参数文件in_file = fopen(in_file_name, "rb");if(!in_file) {printf("open file %s failed\n", in_file_name);return  -1;}out_file = fopen(out_file_name, "wb");if(!out_file) {printf("open file %s failed\n", out_file_name);return  -1;}// 2自定义 iouint8_t *io_buffer = av_malloc(BUF_SIZE);AVIOContext *avio_ctx = avio_alloc_context(io_buffer, BUF_SIZE, 0, (void *)in_file,    \read_packet, NULL, NULL);AVFormatContext *format_ctx = avformat_alloc_context();format_ctx->pb = avio_ctx;int ret = avformat_open_input(&format_ctx, NULL, NULL, NULL);if(ret < 0) {printf("avformat_open_input failed:%s\n", av_err2str(ret));return -1;}// 编码器查找AVCodec *codec = avcodec_find_decoder(AV_CODEC_ID_AAC);if(!codec) {printf("avcodec_find_decoder failed\n");return -1;}AVCodecContext *codec_ctx = avcodec_alloc_context3(codec);if(!codec_ctx) {printf("avcodec_alloc_context3 failed\n");return -1;}ret = avcodec_open2(codec_ctx, codec, NULL);if(ret < 0) {printf("avcodec_open2 failed:%s\n", av_err2str(ret));return -1;}AVPacket *packet = av_packet_alloc();AVFrame *frame = av_frame_alloc();while (1) {ret = av_read_frame(format_ctx, packet);if(ret < 0) {printf("av_read_frame failed:%s\n", av_err2str(ret));break;}decode(codec_ctx, packet, frame, out_file);}printf("read file finish\n");decode(codec_ctx, NULL, frame, out_file);fclose(in_file);fclose(out_file);av_free(io_buffer);av_frame_free(frame);av_packet_free(packet);avformat_close_input(&format_ctx);avcodec_free_context(&codec_ctx);printf("main finish\n");return 0;
}