[英]How to decode one AAC frame at a time using C++?
我想连续解码AAC帧流,一次解码一帧。
我浏览了ffmpeg示例(正确答案不一定需要使用ffmpeg),而我仅找到使用完整AAC文件和批处理算法的示例。 但是我想解码一个连续的AAC流。 我怎样才能做到这一点?
更新:按照注释并在android上使用ffmpeg将AAC解码为PCM ,我能够使用ffmpeg解码为PCM,但是输出的声音非常嘈杂。 当为每个AAC帧调用此方法时,我在做什么错:
...
/*loop that receives frame in buffer*/
while(1){
/*receive frame*/
input = receive_one_buffer();
/*decode frame*/
decodeBuffer(input,strlen(input),Outfile);
}
...
/*decode frame*/
void decodeBuffer(char * input, int numBytes, ofstream& Outfile) {
/*"input" contains one AAC-LC frame*/
//copy bytes from buffer
uint8_t inputBytes[numBytes + FF_INPUT_BUFFER_PADDING_SIZE];
memset(inputBytes, 0, numBytes + FF_INPUT_BUFFER_PADDING_SIZE);
memcpy(inputBytes, input, numBytes);
av_register_all();
AVCodec *codec = avcodec_find_decoder(CODEC_ID_AAC);
AVCodecContext *avCtx = avcodec_alloc_context();
avCtx->channels = 1;
avCtx->sample_rate = 44100;
//the input buffer
AVPacket avPacket;
av_init_packet(&avPacket);
avPacket.size = numBytes; //input buffer size
avPacket.data = inputBytes; // the input buffer
int outSize;
int len;
uint8_t *outbuf = static_cast<uint8_t *>(malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE));
while (avPacket.size > 0) {
outSize = AVCODEC_MAX_AUDIO_FRAME_SIZE;
len = avcodec_decode_audio3(avCtx, (short *) outbuf, &outSize,
&avPacket);
Outfile.write((char*)outbuf, outSize);
avPacket.size -= len;
avPacket.data += len;
}
av_free_packet(&avPacket);
avcodec_close(avCtx);
//av_free(avCtx);
return;
}
您必须在随后的解码调用之间保持解码器处于活动状态。 AAC解码器必须解码先前的缓冲区才能正确地“启动”。
请检查详细信息:
https://developer.apple.com/library/mac/technotes/tn2258/_index.html
以下代码假定“ ReceiveBuffer”函数恰好返回一个完整的AAC访问单元。
(顺便说一句:您不能在二进制缓冲区上使用strlen;您将获得到第一个零的距离,而不是缓冲区长度)
#include <iostream>
#include <fstream>
#include "libavcodec\avcodec.h"
#include "libavformat\avformat.h"
#include "libavdevice\avdevice.h"
#include "libavfilter\avfilter.h"
AVCodecContext * CreateContext()
{
av_register_all();
AVCodec *codec = avcodec_find_decoder(AV_CODEC_ID_AAC);
AVCodecContext *avCtx = avcodec_alloc_context3(codec);
return avCtx;
}
int32_t DecodeBuffer
(
std::ostream & output,
uint8_t * pInput,
uint32_t cbInputSize,
AVCodecContext * pAVContext
)
{
int32_t cbDecoded = 0;
//the input buffer
AVPacket avPacket;
av_init_packet(&avPacket);
avPacket.size = cbInputSize; //input buffer size
avPacket.data = pInput; // the input bufferra
AVFrame * pDecodedFrame = av_frame_alloc();
int nGotFrame = 0;
cbDecoded = avcodec_decode_audio4( pAVContext,
pDecodedFrame,
& nGotFrame,
& avPacket);
int data_size = av_samples_get_buffer_size( NULL,
pAVContext->channels,
pDecodedFrame->nb_samples,
pAVContext->sample_fmt,
1);
output.write((const char*)pDecodedFrame->data[0],data_size);
av_frame_free(&pDecodedFrame);
return cbDecoded;
}
uint8_t * ReceiveBuffer( uint32_t * cbBufferSize)
{
// TODO implement
return NULL;
}
int main
(
int argc,
char *argv[]
)
{
int nResult = 0;
AVCodecContext * pAVContext = CreateContext();
std::ofstream myOutputFile("audio.pcm",std::ios::binary);
while(1)
{
uint32_t cbBufferSize = 0;
uint8_t *pCompressedAudio = ReceiveBuffer( &cbBufferSize);
if(cbBufferSize && pCompressedAudio)
{
DecodeBuffer( myOutputFile,
pCompressedAudio,
cbBufferSize,
pAVContext);
}
else
{
break;
}
}
avcodec_close(pAVContext);
av_free(pAVContext);
return nResult;
}
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