2023-10-13 20:52:26 CST W41D5

examples/encode-audio/main.go

@@ -0,0 +1,183 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"os"
+	"syscall"
+	"unsafe"
+
+	ffmpeg "github.com/qrtc/ffmpeg-dev-go"
+)
+
+// check that a given sample format is supported by the encoder
+func checkSampleFmt(codec *ffmpeg.AvCodec, sampleFmt ffmpeg.AvSampleFormat) int32 {
+	for _, f := range codec.GetSampleFmts() {
+		if f == sampleFmt {
+			return 1
+		}
+	}
+	return 0
+}
+
+func selectSampleRate(codec *ffmpeg.AvCodec) int32 {
+	var bestSamplerate int32
+	ss := codec.GetSupportedSamplerates()
+	if len(ss) == 0 {
+		return 44100
+	}
+	for _, s := range ss {
+		if bestSamplerate == 0 || ffmpeg.FFABS(44100-s) < ffmpeg.FFABS(44100-bestSamplerate) {
+			bestSamplerate = s
+		}
+	}
+	return bestSamplerate
+}
+
+// select layout with the highest channel count
+func selectChannelLayout(codec *ffmpeg.AvCodec) uint64 {
+	var bestChLayout uint64
+	var bestNbChannels int32
+	ls := codec.GetChannelLayouts()
+	if len(ls) == 0 {
+		return ffmpeg.AV_CH_LAYOUT_STEREO
+	}
+
+	for _, l := range ls {
+		nbChannels := ffmpeg.AvGetChannelLayoutNbChannels(l)
+
+		if nbChannels > bestNbChannels {
+			bestChLayout = l
+			bestNbChannels = nbChannels
+		}
+	}
+
+	return bestChLayout
+}
+
+func encode(ctx *ffmpeg.AvCodecContext, frame *ffmpeg.AvFrame, pkt *ffmpeg.AvPacket, output *os.File) {
+	// send the frame for encoding
+	ret := ffmpeg.AvCodecSendFrame(ctx, frame)
+	if ret < 0 {
+		fmt.Fprintf(os.Stderr, "Error sending the frame to the encoder\n")
+		os.Exit(1)
+	}
+
+	// read all the available output packets (in general there may be any number of them
+	for ret >= 0 {
+		ret = ffmpeg.AvCodecReceivePacket(ctx, pkt)
+		if ret == ffmpeg.AVERROR(int32(syscall.EAGAIN)) || ret == ffmpeg.AVERROR_EOF {
+			return
+		} else if ret < 0 {
+			fmt.Fprintf(os.Stderr, "Error encoding audio frame\n")
+			os.Exit(1)
+		}
+
+		output.Write(ffmpeg.Slice(pkt.GetData(), pkt.GetSize()))
+		ffmpeg.AvPacketUnref(pkt)
+	}
+
+}
+
+func main() {
+	if len(os.Args) <= 1 {
+		fmt.Fprintf(os.Stdout, "Usage: %s <output file>\n", os.Args[0])
+		return
+	}
+	filename := os.Args[1]
+
+	// find the MP2 encoder
+	codec := ffmpeg.AvCodecFindEncoder(ffmpeg.AV_CODEC_ID_MP2)
+
+	if codec == nil {
+		fmt.Fprintf(os.Stderr, "Codec not found\n")
+		os.Exit(1)
+	}
+
+	avctx := ffmpeg.AvCodecAllocContext3(codec)
+	if avctx == nil {
+		fmt.Fprintf(os.Stderr, "Could not allocate audio codec context\n")
+		os.Exit(1)
+	}
+
+	// put sample parameters
+	avctx.SetBitRate(64000)
+
+	avctx.SetSampleFmt(ffmpeg.AV_SAMPLE_FMT_S16)
+	if checkSampleFmt(codec, avctx.GetSampleFmt()) == 0 {
+		fmt.Fprintf(os.Stderr, "Encoder does not support sample format %s",
+			ffmpeg.AvGetSampleFmtName(avctx.GetSampleFmt()))
+		os.Exit(1)
+	}
+
+	// select other audio parameters supported by the encoder
+	avctx.SetSampleRate(selectSampleRate(codec))
+	avctx.SetChannelLayout(selectChannelLayout(codec))
+	avctx.SetChannels(ffmpeg.AvGetChannelLayoutNbChannels(avctx.GetChannelLayout()))
+
+	// open it
+	if ffmpeg.AvCodecOpen2(avctx, codec, nil) < 0 {
+		fmt.Fprintf(os.Stderr, "Could not open codec\n")
+		os.Exit(1)
+	}
+
+	f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0755)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Could not open %s\n", filename)
+		os.Exit(1)
+	}
+
+	// packet for holding encoded output
+	pkt := ffmpeg.AvPacketAlloc()
+	if pkt == nil {
+		fmt.Fprintf(os.Stderr, "could not allocate the packet\n")
+		os.Exit(1)
+	}
+
+	frame := ffmpeg.AvFrameAlloc()
+	if frame == nil {
+		fmt.Fprintf(os.Stderr, "Could not allocate audio frame\n")
+		os.Exit(1)
+	}
+
+	frame.SetNbSamples(avctx.GetFrameSize())
+	frame.SetFormat(int32(avctx.GetSampleFmt()))
+	frame.SetChannelLayout(avctx.GetChannelLayout())
+
+	// allocate the data buffers
+	if ret := ffmpeg.AvFrameGetBuffer(frame, 0); ret < 0 {
+		fmt.Fprintf(os.Stderr, "Could not allocate audio data buffers\n")
+		os.Exit(1)
+	}
+
+	// encode a single tone sound
+	t := float64(0)
+	tincr := 2 * math.Pi * 440.0 / float64(avctx.GetSampleRate())
+	for i := 0; i < 200; i++ {
+		// make sure the frame is writable -- makes a copy if the encoder
+		// kept a reference internally
+		if ret := ffmpeg.AvFrameMakeWritable(frame); ret < 0 {
+			os.Exit(1)
+		}
+		samples := unsafe.Slice((*uint16)(unsafe.Pointer(frame.GetDataIdx(0))), 2*avctx.GetFrameSize()+avctx.GetChannels())
+
+		for j := 0; j < int(avctx.GetFrameSize()); j++ {
+			samples[2*j] = (uint16)(math.Sin(t) * 10000)
+
+			for k := 1; k < int(avctx.GetChannels()); k++ {
+				samples[2*j+k] = samples[2*j]
+			}
+			t += tincr
+		}
+		encode(avctx, frame, pkt, f)
+	}
+
+	// flush the encoder
+	encode(avctx, nil, pkt, f)
+
+	f.Close()
+
+	ffmpeg.AvFrameFree(&frame)
+	ffmpeg.AvPacketFree(&pkt)
+	ffmpeg.AvCodecFreeContext(&avctx)
+}