2023-04-15：ffmpeg的filter_audio.c的功能是生成一个正弦波音频，然后通过简单的滤镜链，最后输

2023-04-15：ffmpeg的filter_audio.c的功能是生成一个正弦波音频，然后通过简单的滤镜链，最后输出数据的MD5校验和。请用go语言改写。

答案2023-04-15：

代码见github/moonfdd/ffmpeg-go库。

以下是通过 Go 语言重新实现 ffmpeg 的 filter_audio.c 功能的步骤：

导入必要的依赖包和定义常量和变量。
初始化 FFmpeg 库文件路径。
创建一个音频滤镜图，并将 abuffer、volume 和 aformat 滤镜连接起来。其中，abuffer 滤镜用于获取输入音频采样，volume 滤镜用于调节音频音量，aformat 滤镜用于设置输出音频格式。
创建输出音频流的 AVCodecContext 上下文，并设置相关属性。
使用 avcodec_find_encoder_by_name 函数查找 PCM S16LE 编码器，然后创建编码器的 AVCodec 上下文。
打开编码器并写入头部信息。
循环读取音频帧，将其发送到音频滤镜图进行处理。
从滤镜图中获取输出音频帧，并将其编码为 PCM S16LE 格式。
计算输出音频帧的 MD5 校验和，并将其打印到标准输出上。
释放资源，结束程序运行。

以上就是使用 Go 语言对 filter_audio.c 文件进行重新实现的步骤。

命令如下：

go run ./examples/internalexamples/filter_audio/main.go 1

go代码如下：

package main

import (
    "fmt"
    "math"
    "os"
    "strconv"
    "unsafe"

    "github.com/moonfdd/ffmpeg-go/ffcommon"
    "github.com/moonfdd/ffmpeg-go/libavfilter"
    "github.com/moonfdd/ffmpeg-go/libavutil"
)

func main0() (ret ffcommon.FInt) {
    var md5 *libavutil.AVMD5
    var graph *libavfilter.AVFilterGraph
    var src, sink *libavfilter.AVFilterContext
    var frame *libavutil.AVFrame
    var errstr [1024]ffcommon.FUint8T
    var duration ffcommon.FFloat
    var err, nb_frames, i ffcommon.FInt

    if len(os.Args) < 2 {
        fmt.Printf("Usage: %s <duration>\n", os.Args[0])
        return 1
    }

    f, err2 := strconv.ParseFloat(os.Args[1], 32)
    if err2 != nil {
        // handle error
        return 1
    }
    duration = float32(f)
    nb_frames = int32(float64(duration) * INPUT_SAMPLERATE / FRAME_SIZE)
    if nb_frames <= 0 {
        fmt.Printf("Invalid duration: %s\n", os.Args[1])
        return 1
    }

    /* Allocate the frame we will be using to store the data. */
    frame = libavutil.AvFrameAlloc()
    if frame == nil {
        fmt.Printf("Error allocating the frame\n")
        return 1
    }

    md5 = libavutil.AvMd5Alloc()
    if md5 == nil {
        fmt.Printf("Error allocating the MD5 context\n")
        return 1
    }

    /* Set up the filtergraph. */
    err = init_filter_graph(&graph, &src, &sink)
    if err < 0 {
        fmt.Printf("Unable to init filter graph:")
        goto fail
    }

    /* the main filtering loop */
    for i = 0; i < nb_frames; i++ {
        // /* get an input frame to be filtered */
        err = get_input(frame, i)
        if err < 0 {
            fmt.Printf("Error generating input frame:")
            goto fail
        }

        /* Send the frame to the input of the filtergraph. */
        err = src.AvBuffersrcAddFrame(frame)
        if err < 0 {
            frame.AvFrameUnref()
            fmt.Printf("Error submitting the frame to the filtergraph:")
            goto fail
        }

        /* Get all the filtered output that is available. */
        err = sink.AvBuffersinkGetFrame(frame)
        for err >= 0 {
            /* now do something with our filtered frame */
            err = process_output(md5, frame)
            if err < 0 {
                fmt.Printf("Error processing the filtered frame:")
                goto fail
            }
            frame.AvFrameUnref()
            err = sink.AvBuffersinkGetFrame(frame)
        }

        if err == -libavutil.EAGAIN {
            /* Need to feed more frames in. */
            continue
        } else if err == libavutil.AVERROR_EOF {
            /* Nothing more to do, finish. */
            break
        } else if err < 0 {
            /* An error occurred. */
            fmt.Printf("Error filtering the data:")
            goto fail
        }
    }

    libavfilter.AvfilterGraphFree(&graph)
    libavutil.AvFrameFree(&frame)
    libavutil.AvFreep(uintptr(unsafe.Pointer(&md5)))

    return 0

fail:
    libavutil.AvStrerror(err, (*byte)(unsafe.Pointer(&errstr)), uint64(len(errstr)))
    fmt.Printf("%s\n", errstr)
    return 1
}

const INPUT_SAMPLERATE = 48000
const INPUT_FORMAT = libavutil.AV_SAMPLE_FMT_FLTP
const INPUT_CHANNEL_LAYOUT = libavutil.AV_CH_LAYOUT_5POINT0

const VOLUME_VAL = 0.90

func init_filter_graph(graph **libavfilter.AVFilterGraph, src **libavfilter.AVFilterContext,
    sink **libavfilter.AVFilterContext) ffcommon.FInt {
    var filter_graph *libavfilter.AVFilterGraph
    var abuffer_ctx *libavfilter.AVFilterContext
    var abuffer *libavfilter.AVFilter
    var volume_ctx *libavfilter.AVFilterContext
    var volume *libavfilter.AVFilter
    var aformat_ctx *libavfilter.AVFilterContext
    var aformat *libavfilter.AVFilter
    var abuffersink_ctx *libavfilter.AVFilterContext
    var abuffersink *libavfilter.AVFilter

    var options_dict *libavutil.AVDictionary
    var options_str string
    var ch_layout [64]ffcommon.FUint8T

    var err ffcommon.FInt

    /* Create a new filtergraph, which will contain all the filters. */
    filter_graph = libavfilter.AvfilterGraphAlloc()
    if filter_graph == nil {
        fmt.Printf("Unable to create filter graph.\n")
        return libavutil.ENOMEM
    }

    /* Create the abuffer filter;
     * it will be used for feeding the data into the graph. */
    abuffer = libavfilter.AvfilterGetByName("abuffer")
    if abuffer == nil {
        fmt.Printf("Could not find the abuffer filter.\n")
        return libavutil.AVERROR_FILTER_NOT_FOUND
    }

    abuffer_ctx = filter_graph.AvfilterGraphAllocFilter(abuffer, "src")
    if abuffer_ctx == nil {
        fmt.Printf("Could not allocate the abuffer instance.\n")
        return -libavutil.ENOMEM
    }

    /* Set the filter options through the AVOptions API. */
    libavutil.AvGetChannelLayoutString((*byte)(unsafe.Pointer(&ch_layout)), int32(len(ch_layout)), 0, INPUT_CHANNEL_LAYOUT)
    libavutil.AvOptSet(uintptr(unsafe.Pointer(abuffer_ctx)), "channel_layout", ffcommon.StringFromPtr(uintptr(unsafe.Pointer(&ch_layout))), libavutil.AV_OPT_SEARCH_CHILDREN)
    libavutil.AvOptSet(uintptr(unsafe.Pointer(abuffer_ctx)), "sample_fmt", libavutil.AvGetSampleFmtName(INPUT_FORMAT), libavutil.AV_OPT_SEARCH_CHILDREN)
    libavutil.AvOptSetQ(uintptr(unsafe.Pointer(abuffer_ctx)), "time_base", libavutil.AVRational{1, INPUT_SAMPLERATE}, libavutil.AV_OPT_SEARCH_CHILDREN)
    libavutil.AvOptSetInt(uintptr(unsafe.Pointer(abuffer_ctx)), "sample_rate", INPUT_SAMPLERATE, libavutil.AV_OPT_SEARCH_CHILDREN)

    /* Now initialize the filter; we pass NULL options, since we have already
     * set all the options above. */
    err = abuffer_ctx.AvfilterInitStr("")
    if err < 0 {
        fmt.Printf("Could not initialize the abuffer filter.\n")
        return err
    }

    /* Create volume filter. */
    volume = libavfilter.AvfilterGetByName("volume")
    if volume == nil {
        fmt.Printf("Could not find the volume filter.\n")
        return libavutil.AVERROR_FILTER_NOT_FOUND
    }

    volume_ctx = filter_graph.AvfilterGraphAllocFilter(volume, "volume")
    if volume_ctx == nil {
        fmt.Printf("Could not allocate the volume instance.\n")
        return -libavutil.ENOMEM
    }

    /* A different way of passing the options is as key/value pairs in a
     * dictionary. */
    libavutil.AvDictSet(&options_dict, "volume", fmt.Sprint(VOLUME_VAL), 0)
    err = volume_ctx.AvfilterInitDict(&options_dict)
    libavutil.AvDictFree(&options_dict)
    if err < 0 {
        fmt.Printf("Could not initialize the volume filter.\n")
        return err
    }

    /* Create the aformat filter;
     * it ensures that the output is of the format we want. */
    aformat = libavfilter.AvfilterGetByName("aformat")
    if aformat == nil {
        fmt.Printf("Could not find the aformat filter.\n")
        return libavutil.AVERROR_FILTER_NOT_FOUND
    }

    aformat_ctx = filter_graph.AvfilterGraphAllocFilter(aformat, "aformat")
    if aformat_ctx == nil {
        fmt.Printf("Could not allocate the aformat instance.\n")
        return -libavutil.ENOMEM
    }

    /* A third way of passing the options is in a string of the form
     * key1=value1:key2=value2.... */
    // snprintf(options_str, sizeof(options_str),
    //          "sample_fmts=%s:sample_rates=%d:channel_layouts=0x%"PRIx64,
    //          av_get_sample_fmt_name(AV_SAMPLE_FMT_S16), 44100,
    //          (uint64_t)AV_CH_LAYOUT_STEREO);
    options_str = fmt.Sprintf("sample_fmts=%s:sample_rates=%d:channel_layouts=0x%x",
        libavutil.AvGetSampleFmtName(libavutil.AV_SAMPLE_FMT_S16), 44100,
        libavutil.AV_CH_LAYOUT_STEREO)
    fmt.Println(options_str)
    err = aformat_ctx.AvfilterInitStr(options_str)
    if err < 0 {
        libavutil.AvLog(uintptr(0), libavutil.AV_LOG_ERROR, "Could not initialize the aformat filter.\n")
        return err
    }

    /* Finally create the abuffersink filter;
     * it will be used to get the filtered data out of the graph. */
    abuffersink = libavfilter.AvfilterGetByName("abuffersink")
    if abuffersink == nil {
        fmt.Printf("Could not find the abuffersink filter.\n")
        return libavutil.AVERROR_FILTER_NOT_FOUND
    }

    abuffersink_ctx = filter_graph.AvfilterGraphAllocFilter(abuffersink, "sink")
    if abuffersink_ctx == nil {
        fmt.Printf("Could not allocate the abuffersink instance.\n")
        return -libavutil.ENOMEM
    }

    /* This filter takes no options. */
    err = abuffersink_ctx.AvfilterInitStr("")
    if err < 0 {
        fmt.Printf("Could not initialize the abuffersink instance.\n")
        return err
    }

    /* Connect the filters;
     * in this simple case the filters just form a linear chain. */
    err = abuffer_ctx.AvfilterLink(0, volume_ctx, 0)
    if err >= 0 {
        err = volume_ctx.AvfilterLink(0, aformat_ctx, 0)
    }
    if err >= 0 {
        err = aformat_ctx.AvfilterLink(0, abuffersink_ctx, 0)
    }
    if err < 0 {
        fmt.Printf("Error connecting filters\n")
        return err
    }

    /* Configure the graph. */
    err = filter_graph.AvfilterGraphConfig(uintptr(0))
    if err < 0 {
        libavutil.AvLog(uintptr(0), libavutil.AV_LOG_ERROR, "Error configuring the filter graph\n")
        return err
    }

    *graph = filter_graph
    *src = abuffer_ctx
    *sink = abuffersink_ctx

    return 0
}

/* Do something useful with the filtered data: this simple
 * example just prints the MD5 checksum of each plane to stdout. */
func process_output(md5 *libavutil.AVMD5, frame *libavutil.AVFrame) ffcommon.FInt {
    planar := libavutil.AvSampleFmtIsPlanar(libavutil.AVSampleFormat(frame.Format))
    channels := libavutil.AvGetChannelLayoutNbChannels(frame.ChannelLayout)
    planes := channels
    if planar == 0 {
        planes = 1
    }
    bps := libavutil.AvGetBytesPerSample(libavutil.AVSampleFormat(frame.Format))
    plane_size := bps * frame.NbSamples
    if planar == 0 {
        plane_size = plane_size * channels
    }
    var i, j ffcommon.FInt

    for i = 0; i < planes; i++ {
        var checksum [16]ffcommon.FUint8T

        md5.AvMd5Init()
        ptr := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(frame.ExtendedData)) + uintptr(i*8)))
        libavutil.AvMd5Sum((*byte)(unsafe.Pointer(&checksum)), (*byte)(unsafe.Pointer(ptr)), plane_size)

        fmt.Printf("plane %d: 0x", i)
        for j = 0; j < int32(len(checksum)); j++ {
            fmt.Printf("%02X", checksum[j])
        }
        fmt.Printf("\n")
    }
    fmt.Printf("\n")

    return 0
}

const FRAME_SIZE = 1024

/* Construct a frame of audio data to be filtered;
 * this simple example just synthesizes a sine wave. */
func get_input(frame *libavutil.AVFrame, frame_num ffcommon.FInt) ffcommon.FInt {
    var err, i, j ffcommon.FInt

    // #define FRAME_SIZE 1024

    /* Set up the frame properties and allocate the buffer for the data. */
    frame.SampleRate = INPUT_SAMPLERATE
    frame.Format = INPUT_FORMAT
    frame.ChannelLayout = INPUT_CHANNEL_LAYOUT
    frame.NbSamples = FRAME_SIZE
    frame.Pts = int64(frame_num) * FRAME_SIZE

    err = frame.AvFrameGetBuffer(0)
    if err < 0 {
        return err
    }

    /* Fill the data for each channel. */
    for i = 0; i < 5; i++ {
        // float *data = (float*)frame->extended_data[i];
        ptr := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(frame.ExtendedData)) + uintptr(i*8)))
        data := (*ffcommon.FFloat)(unsafe.Pointer(ptr))

        for j = 0; j < frame.NbSamples; j++ {
            *(*ffcommon.FFloat)(unsafe.Pointer(uintptr(unsafe.Pointer(data)) + uintptr(4*j))) = float32(math.Sin(2 * libavutil.M_PI * (float64(frame_num + j)) * float64((i+1)/FRAME_SIZE)))
        }
    }

    return 0
}

func main() {
    // go run ./examples/internalexamples/filter_audio/main.go 1
    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-7.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
        }
    }

    main0()
}