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)
    }
}