discard buffered frames for < 1fps (#470)

pkg/driver/camera/camera_linux.go

@@ -12,6 +12,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"sync"
+	"time"
 
 	"github.com/blackjack/webcam"
 	"github.com/pion/mediadevices/pkg/driver"
@@ -70,6 +71,7 @@ type camera struct {
 	started         bool
 	mutex           sync.Mutex
 	cancel          func()
+	prevFrameTime   time.Time
 }
 
 func init() {
@@ -158,8 +160,13 @@ func (c *camera) Open() error {
 		return err
 	}
 
-	// Late frames should be discarded. Buffering should be handled in higher level.
+	// Buffering should be handled in higher level.
-	cam.SetBufferCount(1)
+	err = cam.SetBufferCount(1)
+	if err != nil {
+		return err
+	}
+
+	c.prevFrameTime = time.Now()
 	c.cam = cam
 	return nil
 }
@@ -228,6 +235,13 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 				return nil, func() {}, io.EOF
 			}
 
+			if p.DiscardFramesOlderThan != 0 {
+				if time.Now().Sub(c.prevFrameTime) >= p.DiscardFramesOlderThan {
+					_ = cam.WaitForFrame(readTimeoutSec)
+					_, _ = cam.ReadFrame()
+				}
+			}
+
 			err := cam.WaitForFrame(readTimeoutSec)
 			switch err.(type) {
 			case nil:
@@ -244,6 +258,10 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 				return nil, func() {}, err
 			}
 
+			if p.DiscardFramesOlderThan != 0 {
+				c.prevFrameTime = time.Now()
+			}
+
 			// Frame is empty.
 			// Retry reading and return errEmptyFrame if it exceeds maxEmptyFrameCount.
 			if len(b) == 0 {

pkg/prop/prop.go

@@ -9,7 +9,7 @@ import (
 	"github.com/pion/mediadevices/pkg/frame"
 )
 
-// MediaConstraints represents set of media propaty constraints.
+// MediaConstraints represents set of media property constraints.
 // Each field constrains property by min/ideal/max range, exact match, or oneof match.
 type MediaConstraints struct {
 	DeviceID StringConstraint
@@ -229,16 +229,18 @@ func (c *comparisons) fitnessDistance() (float64, bool) {
 
 // VideoConstraints represents a video's constraints
 type VideoConstraints struct {
-	Width, Height IntConstraint
+	Width, Height          IntConstraint
-	FrameRate     FloatConstraint
+	FrameRate              FloatConstraint
-	FrameFormat   FrameFormatConstraint
+	FrameFormat            FrameFormatConstraint
+	DiscardFramesOlderThan time.Duration
 }
 
 // Video represents a video's constraints
 type Video struct {
-	Width, Height int
+	Width, Height          int
-	FrameRate     float32
+	FrameRate              float32
-	FrameFormat   frame.Format
+	FrameFormat            frame.Format
+	DiscardFramesOlderThan time.Duration
 }
 
 // AudioConstraints represents an audio's constraints