2023-03-12：mp3音频解码为pcm，代码用go语言编写，调用moonfdd/ffmpeg-go库。
答案2023-03-12：
用github/moonfdd/ffmpeg-go库。
命令如下：
go run ./examples/a15.audio_decode_mp32pcm/main.go
代码参考了15：mp3音频解码为pcm,代码用golang编写。如下：
package main
import (
"fmt"
"os"
"os/exec"
"unsafe"
"github.com/moonfdd/ffmpeg-go/ffcommon"
"github.com/moonfdd/ffmpeg-go/libavcodec"
"github.com/moonfdd/ffmpeg-go/libavformat"
"github.com/moonfdd/ffmpeg-go/libavutil"
)
func main() {
os.Setenv("Path", os.Getenv("Path")+";./lib")
ffcommon.SetAvutilPath("./lib/avutil-56.dll")
ffcommon.SetAvcodecPath("./lib/avcodec-58.dll")
ffcommon.SetAvdevicePath("./lib/avdevice-58.dll")
ffcommon.SetAvfilterPath("./lib/avfilter-56.dll")
ffcommon.SetAvformatPath("./lib/avformat-58.dll")
ffcommon.SetAvpostprocPath("./lib/postproc-55.dll")
ffcommon.SetAvswresamplePath("./lib/swresample-3.dll")
ffcommon.SetAvswscalePath("./lib/swscale-5.dll")
genDir := "./out"
_, err := os.Stat(genDir)
if err != nil {
if os.IsNotExist(err) {
os.Mkdir(genDir, 0777) // Everyone can read write and execute
}
}
inVFileName := "./out/test.mp3"
outFileName := "./out/test.pcm"
// ./lib/ffmpeg -i ./resources/big_buck_bunny.mp4 -acodec libmp3lame -vn ./out/test.mp3
//是否存在mp3文件
_, err = os.Stat(inVFileName)
if err != nil {
if os.IsNotExist(err) {
fmt.Println("create mp3 file")
exec.Command("./lib/ffmpeg", "-i", "./resources/big_buck_bunny.mp4", "-acodec", "libmp3lame", "-vn", inVFileName, "-y").CombinedOutput()
}
}
os.Remove(outFileName)
f, err := os.OpenFile(outFileName, os.O_CREATE|os.O_RDWR, 0777)
if err != nil {
fmt.Println("open file failed,err:", err)
return
}
fmtCtx := libavformat.AvformatAllocContext()
var codecCtx *libavcodec.AVCodecContext
pkt := libavcodec.AvPacketAlloc()
frame := libavutil.AvFrameAlloc()
aStreamIndex := -1
for {
if libavformat.AvformatOpenInput(&fmtCtx, inVFileName, nil, nil) < 0 {
fmt.Printf("Cannot open input file.\n")
break
}
if fmtCtx.AvformatFindStreamInfo(nil) < 0 {
fmt.Printf("Cannot find stream info in input file.\n")
break
}
fmtCtx.AvDumpFormat(0, inVFileName, 0)
//查找视频流在文件中的位置
for i := uint32(0); i < fmtCtx.NbStreams; i++ {
if fmtCtx.GetStream(i).Codecpar.CodecType == libavutil.AVMEDIA_TYPE_AUDIO {
aStreamIndex = int(i)
break
}
}
if aStreamIndex == -1 {
fmt.Printf("Cannot find audio stream.\n")
return
}
aCodecPara := fmtCtx.GetStream(uint32(aStreamIndex)).Codecpar
codec := libavcodec.AvcodecFindDecoder(aCodecPara.CodecId)
if codec == nil {
fmt.Printf("Cannot find any codec for audio.\n")
return
}
codecCtx = codec.AvcodecAllocContext3()
if codecCtx.AvcodecParametersToContext(aCodecPara) < 0 {
fmt.Printf("Cannot alloc codec context.\n")
return
}
codecCtx.PktTimebase = fmtCtx.GetStream(uint32(aStreamIndex)).TimeBase
if codecCtx.AvcodecOpen2(codec, nil) < 0 {
fmt.Printf("Cannot open audio codec.\n")
return
}
for (fmtCtx.AvReadFrame(pkt)) >= 0 {
if pkt.StreamIndex == uint32(aStreamIndex) {
if codecCtx.AvcodecSendPacket(pkt) >= 0 {
for codecCtx.AvcodecReceiveFrame(frame) >= 0 {
/*
Planar（平面），其数据格式排列方式为 (特别记住，该处是以点nb_samples采样点来交错，不是以字节交错）:
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）
*/
if libavutil.AvSampleFmtIsPlanar(codecCtx.SampleFmt) != 0 {
numBytes := libavutil.AvGetBytesPerSample(codecCtx.SampleFmt)
//pcm播放时是LRLRLR格式，所以要交错保存数据
bytes := []byte{}
for i := int32(0); i < frame.NbSamples; i++ {
for ch := int32(0); ch < codecCtx.Channels; ch++ {
ptr := uintptr(unsafe.Pointer(uintptr(unsafe.Pointer(frame.Data[ch])) + uintptr(numBytes*i)))
for k := int32(0); k < numBytes; k++ {
bytes = append(bytes, *(*byte)(unsafe.Pointer(ptr)))
ptr++
}
}
}
f.Write(bytes)
}
}
}
}
pkt.AvPacketUnref()
}
break
}
libavutil.AvFrameFree(&frame)
libavcodec.AvPacketFree(&pkt)
codecCtx.AvcodecClose()
libavcodec.AvcodecFreeContext(&codecCtx)
fmtCtx.AvformatFreeContext()
f.Close()
fmt.Println("-----------------------------------------")
// ./lib/ffplay -ar 22050 -ac 2 -f f32le -i ./out/test.pcm
_, err = exec.Command("./lib/ffplay.exe", "-ar", "22050", "-ac", "2", "-f", "f32le", "-i", "./out/test.pcm").Output()
if err != nil {
fmt.Println("play err = ", err)
}
}
