Merge branch 'master' of https://bitbucket.org/ausocean/av

cmd/revid-cli/main.go

@@ -6,8 +6,8 @@ DESCRIPTION
   See Readme.md
 
 AUTHORS
-	Saxon A. Nelson-Milton <saxon@ausocean.org>
+  Saxon A. Nelson-Milton <saxon@ausocean.org>
-	Jack Richardson <jack@ausocean.org>
+  Jack Richardson <jack@ausocean.org>
 
 LICENSE
   RevidCLI.go is Copyright (C) 2017-2018 the Australian Ocean Lab (AusOcean)
@@ -20,10 +20,10 @@ LICENSE
   It is distributed in the hope that it will be useful, but WITHOUT
   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
- for more details.
+  for more details.
 
   You should have received a copy of the GNU General Public License
-  along with revid in gpl.txt.  If not, see [GNU licenses](http://www.gnu.org/licenses).
+  along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
 */
 package main
 
@@ -224,7 +224,10 @@ func main() {
 		fmt.Println("Bad vertical flip option!")
 	}
 
-	config.FramesPerClip = *configFlags[framesPerClipPtr]
+	fpc, err := strconv.Atoi(*configFlags[framesPerClipPtr])
+	if err == nil && fpc > 0 {
+		config.FramesPerClip = fpc
+	}
 	config.RtmpUrl = *configFlags[rtmpUrlPtr]
 	config.Bitrate = *configFlags[bitratePtr]
 	config.OutputFileName = *configFlags[outputFileNamePtr]
@@ -241,7 +244,7 @@ func main() {
 	var vs int
 	if *useNetsender {
 		// initialize NetSender and use NetSender's logger
-		config.Logger = netsender.GetLogger()
+		config.Logger = netsender.Logger()
 
 		var err error
 		err = ns.Init(nil, nil, nil)
@@ -267,7 +270,7 @@ func main() {
 			continue
 		}
 
-		if vs != ns.GetVarSum() {
+		if vs != ns.VarSum() {
 			// vars changed
 			vars, err := ns.Vars()
 			if err != nil {
@@ -275,7 +278,7 @@ func main() {
 				time.Sleep(netSendRetryTime)
 				continue
 			}
-			vs = ns.GetVarSum()
+			vs = ns.VarSum()
 			if vars["mode"] == "Paused" {
 				if !paused {
 					config.Logger.Log(progName, "Info", "Pausing revid")
@@ -306,7 +309,7 @@ func sendTo(ns *netsender.Sender) error {
 	inputs := netsender.MakePins(ns.GetConfigParam("ip"), "X")
 	for i, pin := range inputs {
 		if pin.Name == "X23" {
-			inputs[i].Value = int(revidInst.GetBitrate())
+			inputs[i].Value = revidInst.Bitrate()
 		}
 	}
 
@@ -357,9 +360,9 @@ func updateRevid(vars map[string]string, stop bool) {
 	for key, value := range vars {
 		switch key {
 		case "FramesPerClip":
-			asInt, err := strconv.Atoi(value)
+			fpc, err := strconv.Atoi(value)
-			if asInt > 0 && err == nil {
+			if fpc > 0 && err == nil {
-				config.FramesPerClip = value
+				config.FramesPerClip = fpc
 			}
 		case "RtmpUrl":
 			config.RtmpUrl = value

generator/flv_generator.go

@@ -62,15 +62,15 @@ type flvGenerator struct {
 	isGenerating bool
 }
 
-// GetInputChan returns the input channel to the generator. This is where the
+// InputChan returns the input channel to the generator. This is where the
 // raw data frames are entered into the generator
-func (g *flvGenerator) GetInputChan() chan []byte {
+func (g *flvGenerator) InputChan() chan []byte {
 	return g.inputChan
 }
 
-// GetOutputChan retuns the output chan of the generator - this is where the
+// OutputChan retuns the output chan of the generator - this is where the
 // flv packets (more specifically tags) are outputted.
-func (g *flvGenerator) GetOutputChan() chan []byte {
+func (g *flvGenerator) OutputChan() <-chan []byte {
 	return g.outputChan
 }
 

generator/generator.go

@@ -28,8 +28,8 @@ LICENSE
 package generator
 
 type Generator interface {
-	GetInputChan() chan []byte
+	InputChan() chan []byte
-	GetOutputChan() chan []byte
+	OutputChan() <-chan []byte
 	Start()
 	Stop()
 }

generator/mpegts_generator.go

@@ -86,15 +86,15 @@ type tsGenerator struct {
 	isGenerating    bool
 }
 
-// getInputChan returns a handle to the nalInputChan (inputChan) so that nal units
+// InputChan returns a handle to the nalInputChan (inputChan) so that nal units
 // can be passed to the generator and processed
-func (g *tsGenerator) GetInputChan() chan []byte {
+func (g *tsGenerator) InputChan() chan []byte {
 	return g.nalInputChan
 }
 
-// GetOutputChan returns a handle to the generator output chan where the mpegts
+// OutputChan returns a handle to the generator output chan where the mpegts
 // packets will show up once ready to go
-func (g *tsGenerator) GetOutputChan() chan []byte {
+func (g *tsGenerator) OutputChan() <-chan []byte {
 	return g.outputChan
 }
 

parser/h264.go

@@ -37,9 +37,9 @@ const (
 	outputBufferSize = 10000
 )
 
-// h264Parser provides properties and methods to allow for the parsing of a
+// H264 provides properties and methods to allow for the parsing of a
 // h264 stream - i.e. to allow extraction of the individual access units
-type h264Parser struct {
+type H264 struct {
 	inputBuffer         []byte
 	isParsing           bool
 	parserOutputChanRef chan []byte
@@ -48,9 +48,9 @@ type h264Parser struct {
 	delay               uint
 }
 
-// NewH264Parser returns an instance of the h264Parser struct
+// NewH264Parser returns an instance of the H264 struct
-func NewH264Parser() (p *h264Parser) {
+func NewH264Parser() (p *H264) {
-	p = new(h264Parser)
+	p = new(H264)
 	p.isParsing = true
 	p.inputChan = make(chan byte, inputChanSize)
 	p.delay = 0
@@ -60,12 +60,12 @@ func NewH264Parser() (p *h264Parser) {
 // Stop simply sets the isParsing flag to false to indicate to the parser that
 // we don't want to interpret incoming data anymore - this will also make the
 // parser jump out of the parse func
-func (p *h264Parser) Stop() {
+func (p *H264) Stop() {
 	p.isParsing = false
 }
 
 // Start starts the parse func as a goroutine so that incoming data is interpreted
-func (p *h264Parser) Start() {
+func (p *H264) Start() {
 	p.isParsing = true
 	go p.parse()
 }
@@ -73,31 +73,31 @@ func (p *h264Parser) Start() {
 // SetDelay sets a delay inbetween each buffer output. Useful if we're parsing
 // a file but want to replicate the speed of incoming video frames from a
 // camera
-func (p *h264Parser) SetDelay(delay uint) {
+func (p *H264) SetDelay(delay uint) {
 	p.delay = delay
 }
 
-// GetInputChan returns a handle to the input channel of the parser
+// InputChan returns a handle to the input channel of the parser
-func (p *h264Parser) GetInputChan() chan byte {
+func (p *H264) InputChan() chan byte {
 	return p.inputChan
 }
 
-// GetOutputChan returns a handle to the output chan of the parser
+// OutputChan returns a handle to the output chan of the parser
-func (p *h264Parser) GetOutputChan() chan []byte {
+func (p *H264) OutputChan() <-chan []byte {
 	return p.userOutputChanRef
 }
 
 // SetOutputChan sets the parser output chan to the passed output chan. This is
 // useful if we want the parser output to go directly to a generator of some sort
 // for packetization.
-func (p *h264Parser) SetOutputChan(aChan chan []byte) {
+func (p *H264) SetOutputChan(o chan []byte) {
-	p.parserOutputChanRef = aChan
+	p.parserOutputChanRef = o
-	p.userOutputChanRef = aChan
+	p.userOutputChanRef = o
 }
 
 // parse interprets an incoming h264 stream and extracts individual frames
 // aka access units
-func (p *h264Parser) parse() {
+func (p *H264) parse() {
 	outputBuffer := make([]byte, 0, outputBufferSize)
 	searchingForEnd := false
 	for p.isParsing {

parser/mjpeg.go

@@ -29,7 +29,7 @@ package parser
 
 const frameStartCode = 0xD8
 
-type mjpegParser struct {
+type MJPEG struct {
 	inputBuffer         []byte
 	isParsing           bool
 	parserOutputChanRef chan []byte
@@ -38,39 +38,39 @@ type mjpegParser struct {
 	delay               uint
 }
 
-func NewMJPEGParser(inputChanLen int) (p *mjpegParser) {
+func NewMJPEGParser(inputChanLen int) (p *MJPEG) {
-	p = new(mjpegParser)
+	p = new(MJPEG)
 	p.isParsing = true
 	p.inputChan = make(chan byte, inputChanLen)
 	return
 }
 
-func (p *mjpegParser) Stop() {
+func (p *MJPEG) Stop() {
 	p.isParsing = false
 }
 
-func (p *mjpegParser) Start() {
+func (p *MJPEG) Start() {
 	go p.parse()
 }
 
-func (p *mjpegParser) SetDelay(delay uint) {
+func (p *MJPEG) SetDelay(delay uint) {
 	p.delay = delay
 }
 
-func (p *mjpegParser) GetInputChan() chan byte {
+func (p *MJPEG) InputChan() chan byte {
 	return p.inputChan
 }
 
-func (p *mjpegParser) GetOutputChan() chan []byte {
+func (p *MJPEG) OutputChan() <-chan []byte {
 	return p.userOutputChanRef
 }
 
-func (p *mjpegParser) SetOutputChan(aChan chan []byte) {
+func (p *MJPEG) SetOutputChan(o chan []byte) {
-	p.parserOutputChanRef = aChan
+	p.parserOutputChanRef = o
-	p.userOutputChanRef = aChan
+	p.userOutputChanRef = o
 }
 
-func (p *mjpegParser) parse() {
+func (p *MJPEG) parse() {
 	var outputBuffer []byte
 	for p.isParsing {
 		aByte := <-p.inputChan

parser/parser.go

@@ -43,8 +43,8 @@ var (
 type Parser interface {
 	Stop()
 	Start()
-	GetInputChan() chan byte
+	InputChan() chan byte
-	GetOutputChan() chan []byte
+	OutputChan() <-chan []byte
 	SetOutputChan(achan chan []byte)
 	SetDelay(delay uint)
 }

revid/config.go

@@ -46,7 +46,7 @@ type Config struct {
 	Verbosity          uint8
 	HorizontalFlip     uint8
 	VerticalFlip       uint8
-	FramesPerClip      string
+	FramesPerClip      int
 	RtmpUrl            string
 	Bitrate            string
 	OutputFileName     string
@@ -97,7 +97,7 @@ const (
 	defaultQuantization       = "40"
 	defaultBitrate            = "500000"
 	defaultQuantizationMode   = QuantizationOff
-	defaultFramesPerClip      = "1"
+	defaultFramesPerClip      = 1
 	defaultVerticalFlip       = No
 	defaultHorizontalFlip     = No
 )
@@ -171,7 +171,6 @@ func (c *Config) Validate(r *Revid) error {
 	}
 
 	switch c.Output {
-	case Http:
 	case File:
 	case NativeRtmp, FfmpegRtmp:
 		if c.RtmpUrl == "" {
@@ -180,10 +179,14 @@ func (c *Config) Validate(r *Revid) error {
 			break
 		}
 		r.Log(Info, "Defaulting frames per clip to 1 for rtmp output!")
-		c.FramesPerClip = "1"
+		c.FramesPerClip = 1
 	case NothingDefined:
 		r.Log(Warning, "No output defined, defaulting to httpOut!")
 		c.Output = defaultOutput
+		fallthrough
+	case Http:
+		r.Log(Info, "Defaulting frames per clip to 7 for http output!")
+		c.FramesPerClip = 7
 	default:
 		return errors.New("Bad output type defined in config!")
 	}
@@ -219,13 +222,9 @@ func (c *Config) Validate(r *Revid) error {
 		return errors.New("Bad vertical flip option defined in config!")
 	}
 
-	if c.FramesPerClip == "" {
+	if c.FramesPerClip < 1 {
 		r.Log(Warning, "No FramesPerClip defined defined, defaulting to 1!")
 		c.FramesPerClip = defaultFramesPerClip
-	} else {
-		if integer, err := strconv.Atoi(c.FramesPerClip); integer <= 0 || err != nil {
-			return errors.New("Bad width defined in config!")
-		}
 	}
 
 	if c.Width == "" {

revid/revid.go

@@ -83,23 +83,23 @@ const (
 // Revid provides methods to control a revid session; providing methods
 // to start, stop and change the state of an instance using the Config struct.
 type Revid struct {
-	ffmpegPath     string
+	ffmpegPath  string
-	tempDir        string
+	tempDir     string
-	ringBuffer     *ring.Buffer
+	ringBuffer  *ring.Buffer
-	config         Config
+	config      Config
-	isRunning      bool
+	isRunning   bool
-	inputFile      *os.File
+	inputFile   *os.File
-	generator      generator.Generator
+	generator   generator.Generator
-	parser         parser.Parser
+	parser      parser.Parser
-	cmd            *exec.Cmd
+	cmd         *exec.Cmd
-	inputReader    *bufio.Reader
+	inputReader *bufio.Reader
-	ffmpegStdin    io.WriteCloser
+	ffmpegStdin io.WriteCloser
-	outputChan     chan []byte
+	outputChan  chan []byte
-	setupInput     func() error
+	setupInput  func() error
-	getFrame       func() []byte
+	getFrame    func() []byte
-	destination    loadSender
+	destination loadSender
-	rtmpInst       rtmp.Session
+	rtmpInst    rtmp.Session
-	currentBitrate int64
+	bitrate     int
 }
 
 // NewRevid returns a pointer to a new Revid with the desired
@@ -116,14 +116,18 @@ func New(c Config) (*Revid, error) {
 	return &r, nil
 }
 
-// Returns the currently saved bitrate from the most recent bitrate check
+// Bitrate returns the result of the  most recent bitrate check.
-// check bitrate output delay in consts for this period
+func (r *Revid) Bitrate() int {
-func (r *Revid) GetBitrate() int64 {
+	return r.bitrate
-	return r.currentBitrate
 }
 
-// GetConfigRef returns a pointer to the revidInst's Config struct object
+// Config returns the Revid's config.
-func (r *Revid) GetConfigRef() *Config {
+func (r *Revid) Config() *Config {
+	// FIXME(kortschak): This is a massive footgun and should not exist.
+	// Since the config's fields are accessed in running goroutines, any
+	// mutation is a data race. With bad luck a data race is possible by
+	// reading the returned value since it is possible for the running
+	// Ravid to mutate the config it holds.
 	return &r.config
 }
 
@@ -163,7 +167,7 @@ func (r *Revid) reset(config Config) error {
 		}
 		r.destination = s
 	case Http:
-		r.destination = newHttpSender(config.RtmpUrl, httpTimeout, r.Log)
+		r.destination = newHttpSender(config.HttpAddress, httpTimeout, r.Log)
 	}
 
 	switch r.config.Input {
@@ -199,13 +203,13 @@ func (r *Revid) reset(config Config) error {
 	// We have packetization of some sort, so we want to send data to Generator
 	// to perform packetization
 	r.getFrame = r.getFramePacketization
-	r.parser.SetOutputChan(r.generator.GetInputChan())
+	r.parser.SetOutputChan(r.generator.InputChan())
 
 	return nil
 }
 
-// ChangeConfig changes the current configuration of the Revid instance.
+// SetConfig changes the current configuration of the receiver.
-func (r *Revid) ChangeConfig(c Config) error {
+func (r *Revid) SetConfig(c Config) error {
 	// FIXME(kortschak): This is reimplemented in cmd/revid-cli/main.go.
 	// The implementation in the command is used and this is not.
 	// Decide on one or the other.
@@ -233,7 +237,7 @@ func (r *Revid) Log(logType, m string) {
 	fmt.Println(logType + ": " + m)
 }
 
-// IsRunning returns true if the revid is currently running and false otherwise
+// IsRunning returns whether the receiver is running.
 func (r *Revid) IsRunning() bool {
 	return r.isRunning
 }
@@ -296,7 +300,7 @@ func (r *Revid) getFrameNoPacketization() []byte {
 // getFramePacketization gets a frame from the generators output chan - the
 // the generator being an mpegts or flv generator depending on the config
 func (r *Revid) getFramePacketization() []byte {
-	return <-r.generator.GetOutputChan()
+	return <-r.generator.OutputChan()
 }
 
 // packClips takes data segments; whether that be tsPackets or mjpeg frames and
@@ -308,7 +312,7 @@ func (r *Revid) packClips() {
 		select {
 		// TODO: This is temporary, need to work out how to make this work
 		// for cases when there is not packetisation.
-		case frame := <-r.generator.GetOutputChan():
+		case frame := <-r.generator.OutputChan():
 			lenOfFrame := len(frame)
 			if lenOfFrame > ringBufferElementSize {
 				r.Log(Warning, fmt.Sprintf("Frame was too big: %v bytes, getting another one!", lenOfFrame))
@@ -317,26 +321,22 @@ func (r *Revid) packClips() {
 			}
 			_, err := r.ringBuffer.Write(frame)
 			if err != nil {
-				r.Log(Error, err.Error())
 				if err == ring.ErrDropped {
 					r.Log(Warning, fmt.Sprintf("dropped %d byte frame", len(frame)))
+				} else {
+					r.Log(Error, err.Error())
 				}
 			}
 			packetCount++
 			clipSize += lenOfFrame
-			fpcAsInt, err := strconv.Atoi(r.config.FramesPerClip)
+			if packetCount >= r.config.FramesPerClip {
-			if err != nil {
-				r.Log(Error, "Frames per clip not quite right! Defaulting to 1!")
-				r.config.FramesPerClip = "1"
-			}
-			if packetCount >= fpcAsInt {
 				r.ringBuffer.Flush()
 				clipSize = 0
 				packetCount = 0
 				continue
 			}
 		default:
-			time.Sleep(time.Duration(5) * time.Millisecond)
+			time.Sleep(5 * time.Millisecond)
 		}
 	}
 }
@@ -417,8 +417,9 @@ func (r *Revid) outputClips() {
 		now = time.Now()
 		deltaTime := now.Sub(prevTime)
 		if deltaTime > bitrateTime {
-			r.currentBitrate = int64(float64(bytes*8) / float64(deltaTime/1e9))
+			// FIXME(kortschak): For subsecond deltaTime, this will give infinite bitrate.
-			r.Log(Debug, fmt.Sprintf("Bitrate: %v bits/s\n", r.currentBitrate))
+			r.bitrate = int(float64(bytes*8) / float64(deltaTime/time.Second))
+			r.Log(Debug, fmt.Sprintf("Bitrate: %v bits/s\n", r.bitrate))
 			r.Log(Debug, fmt.Sprintf("Ring buffer size: %v\n", r.ringBuffer.Len()))
 			prevTime = now
 			bytes = 0
@@ -513,7 +514,7 @@ func (r *Revid) readCamera() {
 			r.Log(Error, "No data from camera!")
 			time.Sleep(cameraRetryPeriod)
 		default:
-			r.parser.GetInputChan() <- data[0]
+			r.parser.InputChan() <- data[0]
 		}
 	}
 	r.Log(Info, "Not trying to read from camera anymore!")
@@ -542,7 +543,7 @@ func (r *Revid) readFile() error {
 		return err
 	}
 	for i := range data {
-		r.parser.GetInputChan() <- data[i]
+		r.parser.InputChan() <- data[i]
 	}
 	r.inputFile.Close()
 	return nil

revid/senders.go

@@ -29,8 +29,6 @@ LICENSE
 package revid
 
 import (
-	"bytes"
-	"fmt"
 	"io"
 	"os"
 	"os/exec"
@@ -107,8 +105,6 @@ type httpSender struct {
 
 	log func(lvl, msg string)
 
-	buf []byte
-
 	chunk *ring.Chunk
 }
 
@@ -123,32 +119,30 @@ func newHttpSender(_ string, _ time.Duration, log func(lvl, msg string)) *httpSe
 
 func (s *httpSender) load(c *ring.Chunk) error {
 	s.chunk = c
-	buf := bytes.NewBuffer(s.buf[:0])
-	_, err := s.chunk.WriteTo(buf)
-	s.buf = buf.Bytes()
-	if err != nil {
-		return fmt.Errorf("httpSender: %v", err)
-	}
 	return nil
 }
 
 func (s *httpSender) send() error {
+	if s.chunk == nil {
+		// Do not retry with httpSender,
+		// so just return without error
+		// if the chunk has been cleared.
+		return nil
+	}
 	pins := netsender.MakePins("V0", "")
-	pins[0].Value = len(s.buf)
+	pins[0].Value = s.chunk.Len()
-	pins[0].Data = s.buf
+	pins[0].Data = s.chunk.Bytes()
 	pins[0].MimeType = "video/mp2t"
 	_, _, err := s.client.Send(netsender.RequestPoll, pins)
-	if err != nil {
+	// We will not retry, so release
-		return err
+	// the chunk and clear it now.
-	}
-	return nil
-}
-
-func (s *httpSender) release() {
 	s.chunk.Close()
 	s.chunk = nil
+	return err
 }
 
+func (s *httpSender) release() {}
+
 func (s *httpSender) close() error { return nil }
 
 // ffmpegSender implements loadSender for an FFMPEG RTMP destination.
@@ -223,7 +217,7 @@ func newRtmpSender(url string, timeout uint, retries int, log func(lvl, msg stri
 	var err error
 	for n := 0; n < retries; n++ {
 		sess = rtmp.NewSession(url, timeout)
-		err = sess.StartSession()
+		err = sess.Open()
 		if err == nil {
 			break
 		}
@@ -269,7 +263,7 @@ func (s *rtmpSender) restart() error {
 	}
 	for n := 0; n < s.retries; n++ {
 		s.sess = rtmp.NewSession(s.url, s.timeout)
-		err = s.sess.StartSession()
+		err = s.sess.Open()
 		if err == nil {
 			break
 		}

rtmp/rtmp.c

@@ -34,30 +34,29 @@ LICENSE
 #include <rtmp.h>
 
 RTMP* start_session(RTMP* rtmp, char* url, uint connect_timeout) {
-	printf("RTMP url: %s\n", url);
 	rtmp = RTMP_Alloc();
 	RTMP_Init(rtmp);
 	rtmp->Link.timeout = connect_timeout;
 	if (!RTMP_SetupURL(rtmp, url)) {
-		printf("Can't setup url!\n");
 		RTMP_Close(rtmp);
 		RTMP_Free(rtmp);
+		errno = EINVAL;
 		return NULL;
 	}
 
 	RTMP_EnableWrite(rtmp);
 	RTMP_SetBufferMS(rtmp, 3600 * 1000);
 	if (!RTMP_Connect(rtmp, NULL)) {
-		printf("RTMP can't connect!\n");
 		RTMP_Close(rtmp);
 		RTMP_Free(rtmp);
+		errno = EIO;
 		return NULL;
 	}
 
 	if (!RTMP_ConnectStream(rtmp, 0)) {
-		printf("RTMP can't connect stream!\n");
 		RTMP_Close(rtmp);
 		RTMP_Free(rtmp);
+		errno = EIO;
 		return NULL;
 	}
 
@@ -66,13 +65,11 @@ RTMP* start_session(RTMP* rtmp, char* url, uint connect_timeout) {
 
 unsigned int write_frame(RTMP* rtmp, char* data, uint data_length) {
 	if (!RTMP_IsConnected(rtmp)) {
-		printf("RTMP is not connected!\n");
 		return 1;
 	}
 
 	if (!RTMP_Write(rtmp, (const char*)data, data_length)) {
-		printf("RTMP write error!\n");
+		return 2;
-		return 1;
 	}
 
 	return 0;
@@ -80,8 +77,7 @@ unsigned int write_frame(RTMP* rtmp, char* data, uint data_length) {
 
 unsigned int end_session(RTMP* rtmp) {
 	if (rtmp == NULL) {
-		printf("Tried to end RTMP session, but not allocated yet!\n");
+		return 3;
-		return 1;
 	}
 
 	RTMP_Close(rtmp);

rtmp/rtmp.go

@@ -43,12 +43,13 @@ import "C"
 
 import (
 	"errors"
+	"strconv"
 	"unsafe"
 )
 
 // Session provides an interface for sending flv tags over rtmp.
 type Session interface {
-	StartSession() error
+	Open() error
 	Write([]byte) (int, error)
 	Close() error
 }
@@ -71,15 +72,16 @@ func NewSession(url string, connectTimeout uint) Session {
 	}
 }
 
-// StartSession establishes an rtmp connection with the url passed into the
+// Open establishes an rtmp connection with the url passed into the
 // constructor
-func (s *session) StartSession() error {
+func (s *session) Open() error {
 	if s.rtmp != nil {
 		return errors.New("rtmp: attempt to start already running session")
 	}
-	s.rtmp = C.start_session(s.rtmp, C.CString(s.url), C.uint(s.timeout))
+	var err error
+	s.rtmp, err = C.start_session(s.rtmp, C.CString(s.url), C.uint(s.timeout))
 	if s.rtmp == nil {
-		return errors.New("RTMP start error! Check rtmp log for details!")
+		return err
 	}
 	return nil
 }
@@ -87,10 +89,11 @@ func (s *session) StartSession() error {
 // Write writes a frame (flv tag) to the rtmp connection
 func (s *session) Write(data []byte) (int, error) {
 	if s.rtmp == nil {
-		return 0, errors.New("rtmp: attempt to write to non-running session")
+		return 0, Err(3)
 	}
-	if C.write_frame(s.rtmp, (*C.char)(unsafe.Pointer(&data[0])), C.uint(len(data))) != 0 {
+	ret := C.write_frame(s.rtmp, (*C.char)(unsafe.Pointer(&data[0])), C.uint(len(data)))
-		return 0, errors.New("RTMP write error! Check rtmp log for details!")
+	if ret != 0 {
+		return 0, Err(ret)
 	}
 	return len(data), nil
 }
@@ -98,12 +101,30 @@ func (s *session) Write(data []byte) (int, error) {
 // Close terminates the rtmp connection
 func (s *session) Close() error {
 	if s.rtmp == nil {
-		return errors.New("Tried to stop rtmp session, but not running!")
+		return Err(3)
 	}
 	ret := C.end_session(s.rtmp)
 	s.rtmp = nil
 	if ret != 0 {
-		return errors.New("RTMP end session error! Check rtmp log for details!")
+		return Err(ret)
 	}
 	return nil
 }
+
+var rtmpErrs = [...]string{
+	1: "rtmp: not connected",
+	2: "rtmp: write error",
+	3: "rtmp: not started",
+}
+
+type Err uint
+
+func (e Err) Error() string {
+	if 0 <= int(e) && int(e) < len(rtmpErrs) {
+		s := rtmpErrs[e]
+		if s != "" {
+			return s
+		}
+	}
+	return "rtmp: " + strconv.Itoa(int(e))
+}