improve examples (#708)

examples/client-record-format-opus/opus_encoder.go

@@ -0,0 +1,153 @@
+package main
+
+import (
+	"fmt"
+	"unsafe"
+)
+
+// #cgo pkg-config: libavcodec libavutil
+// #include <libavcodec/avcodec.h>
+import "C"
+
+func frameData(frame *C.AVFrame) **C.uint8_t {
+	return (**C.uint8_t)(unsafe.Pointer(&frame.data[0]))
+}
+
+func frameLineSize(frame *C.AVFrame) *C.int {
+	return (*C.int)(unsafe.Pointer(&frame.linesize[0]))
+}
+
+func switchEndianness16(samples []byte) []byte {
+	ls := len(samples)
+	for i := 0; i < ls; i += 2 {
+		samples[i], samples[i+1] = samples[i+1], samples[i]
+	}
+	return samples
+}
+
+// opusEncoder is a wrapper around FFmpeg's Opus encoder.
+type opusEncoder struct {
+	Width  int
+	Height int
+	FPS    int
+
+	codecCtx         *C.AVCodecContext
+	frame            *C.AVFrame
+	pkt              *C.AVPacket
+	samplesBuffer    []byte
+	samplesBufferPTS int64
+}
+
+// initialize initializes a opusEncoder.
+func (d *opusEncoder) initialize() error {
+	codec := C.avcodec_find_encoder(C.AV_CODEC_ID_OPUS)
+	if codec == nil {
+		return fmt.Errorf("avcodec_find_encoder() failed")
+	}
+
+	d.codecCtx = C.avcodec_alloc_context3(codec)
+	if d.codecCtx == nil {
+		return fmt.Errorf("avcodec_alloc_context3() failed")
+	}
+
+	d.codecCtx.bit_rate = 64000
+	d.codecCtx.sample_fmt = C.AV_SAMPLE_FMT_S16
+	d.codecCtx.sample_rate = 48000
+	d.codecCtx.channel_layout = C.AV_CH_LAYOUT_MONO
+	d.codecCtx.channels = C.av_get_channel_layout_nb_channels(d.codecCtx.channel_layout)
+
+	res := C.avcodec_open2(d.codecCtx, codec, nil)
+	if res < 0 {
+		C.avcodec_close(d.codecCtx)
+		return fmt.Errorf("avcodec_open2() failed")
+	}
+
+	d.frame = C.av_frame_alloc()
+	if d.frame == nil {
+		C.avcodec_close(d.codecCtx)
+		return fmt.Errorf("av_frame_alloc() failed")
+	}
+
+	d.frame.nb_samples = d.codecCtx.frame_size
+	d.frame.format = (C.int)(d.codecCtx.sample_fmt)
+	d.frame.channel_layout = d.codecCtx.channel_layout
+
+	res = C.av_frame_get_buffer(d.frame, 0)
+	if res < 0 {
+		C.av_frame_free(&d.frame)
+		C.avcodec_close(d.codecCtx)
+		return fmt.Errorf("av_frame_get_buffer() failed")
+	}
+
+	d.pkt = C.av_packet_alloc()
+	if d.pkt == nil {
+		C.av_frame_free(&d.frame)
+		C.avcodec_close(d.codecCtx)
+		return fmt.Errorf("av_packet_alloc() failed")
+	}
+
+	return nil
+}
+
+// close closes the decoder.
+func (d *opusEncoder) close() {
+	C.av_packet_free(&d.pkt)
+	C.av_frame_free(&d.frame)
+	C.avcodec_close(d.codecCtx)
+}
+
+// encode encodes LPCM samples into Opus packets.
+func (d *opusEncoder) encode(samples []byte) ([][]byte, int64, error) {
+	// convert from big-endian to little-endian
+	samples = switchEndianness16(samples)
+
+	// put samples into an internal buffer
+	d.samplesBuffer = append(d.samplesBuffer, samples...)
+
+	// split buffer into AVFrames
+	requiredSampleSize := (int)(d.codecCtx.frame_size) * 2
+	frameCount := len(d.samplesBuffer) / requiredSampleSize
+	if frameCount == 0 {
+		return nil, 0, fmt.Errorf("sample buffer is not filled enough")
+	}
+
+	ret := make([][]byte, frameCount)
+	var pts int64
+
+	for i := 0; i < frameCount; i++ {
+		samples = d.samplesBuffer[:requiredSampleSize]
+		d.samplesBuffer = d.samplesBuffer[requiredSampleSize:]
+
+		samplePTS := d.samplesBufferPTS
+		d.samplesBufferPTS += int64(len(samples) / 2)
+
+		// pass samples pointer to frame
+		d.frame.data[0] = (*C.uint8_t)(&samples[0])
+
+		// send frame to the encoder
+		d.frame.pts = (C.int64_t)(samplePTS)
+		res := C.avcodec_send_frame(d.codecCtx, d.frame)
+		if res < 0 {
+			return nil, 0, fmt.Errorf("avcodec_send_frame() failed")
+		}
+
+		// wait for result
+		res = C.avcodec_receive_packet(d.codecCtx, d.pkt)
+		if res < 0 {
+			return nil, 0, fmt.Errorf("avcodec_receive_packet() failed")
+		}
+
+		// perform a deep copy of the data before unreferencing the packet
+		data := C.GoBytes(unsafe.Pointer(d.pkt.data), d.pkt.size)
+
+		if i == 0 {
+			pts = (int64)(d.pkt.pts)
+		}
+
+		C.av_packet_unref(d.pkt)
+
+		ret[i] = data
+	}
+
+	return ret, pts, nil
+}