内存IO模式：avio_alloc_context()
/**
* Allocate and initialize an AVIOContext for buffered I/O. It must be later
* freed with avio_context_free().
*
* @param buffer Memory block for input/output operations via AVIOContext.
* The buffer must be allocated with av_malloc() and friends.
* It may be freed and replaced with a new buffer by libavformat.
* AVIOContext.buffer holds the buffer currently in use,
* which must be later freed with av_free().
* @param buffer_size The buffer size is very important for performance.
* For protocols with fixed blocksize it should be set to this blocksize.
* For others a typical size is a cache page, e.g. 4kb.
* @param write_flag Set to 1 if the buffer should be writable, 0 otherwise.
* @param opaque An opaque pointer to user-specific data.
* @param read_packet A function for refilling the buffer, may be NULL.
* For stream protocols, must never return 0 but rather
* a proper AVERROR code.
* @param write_packet A function for writing the buffer contents, may be NULL.
* The function may not change the input buffers content.
* @param seek A function for seeking to specified byte position, may be NULL.
*
* @return Allocated AVIOContext or NULL on failure.
*/
AVIOContext *avio_alloc_context(
unsigned char *buffer,
int buffer_size,
int write_flag,
void *opaque,
int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),
int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
int64_t (*seek)(void *opaque, int64_t offset, int whence)
);
opaque是 read_packet / write_packet 的第⼀个参数，指向⽤户数据。
buffer和buffer_size是 read_packet / write_packet 的第⼆个和第三个参数，是供FFmpeg使⽤的数据区。
buffer ⽤作FFmpeg输⼊时，由⽤户负责向 buffer 中填充数据，FFmpeg取⾛数据。
buffer ⽤作FFmpeg输出时，由FFmpeg负责向 buffer 中填充数据，⽤户取⾛数据。
write_flag是缓冲区读写标志，读写的主语是指FFmpeg。
write_flag 为1时， buffer ⽤于写，即作为FFmpeg输出。
write_flag 为0时， buffer ⽤于读，即作为FFmpeg输⼊。
read_packet和write_packet是函数指针，指向⽤户编写的回调函数。
seek也是函数指针，需要⽀持seek时使⽤。 可以类⽐fseek的机制。
案例：avio_decode_audio
.pro
TEMPLATE = app
CONFIG += console
CONFIG -= app_bundle
CONFIG -= qt
SOURCES += main.c
win32 {
INCLUDEPATH += $$PWD/ffmpeg-4.2.1-win32-dev/include
LIBS += $$PWD/ffmpeg-4.2.1-win32-dev/lib/avformat.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/avcodec.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/avdevice.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/avfilter.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/avutil.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/postproc.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/swresample.lib \
$$PWD/ffmpeg-4.2.1-win32-dev/lib/swscale.lib
}
main.c
/**
* @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 20480
static 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 io
uint8_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;
}
believe.aac believe.pcm
cd E:\Ovoice\av_media\online\07-ffmpeg-decode\build-07-09-avio_decode_audio-Desktop_Qt_5_10_1_MinGW_32bit-Debug
ffplay -ar 48000 -ac 2 -f f32le believe.pcm
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