Merge pull request #7 from liuxuan30/H264

Add a H264 video decoder

.codebeatignore

@@ -0,0 +1 @@
+TelloVideoDecoder/**

.codecov.yml

@@ -1,3 +1,4 @@
 ignore:
   - "TelloSwiftTests"
   - "Package.swift"
+  - "TelloVideoDecoder"

README.md

@@ -14,6 +14,7 @@ TelloSwift is built upon SwiftNIO purely in Swift, providing flexible protocols
 * Event-driven duplex command handlers based on SwiftNIO, powering sync and async command execution;
 * Many useful built-in control commands to design your own flight flow;
 * Full coverage for both Tello SDK and Tello 2.0 SDK (except for swarm)
+* Provide a default H264 video decoder, more details [here](https://github.com/liuxuan30/TelloSwift/tree/master/TelloVideoDecoder) 
 
 ## Requirement
 * Xcode 11 / Swift 5
@@ -95,4 +96,3 @@ It will directly forward the raw stream bytes to the delegate. To turn on the ca
 
 ## TODO list
 1. Swarm support
-2. Better video streaming solution

TelloSwift/Tello.swift

@@ -170,12 +170,21 @@ open class Tello {
             RunLoop.main.add(kaTimer!, forMode: .common)
         }
     }
-
+
+    /// Invalidate timer and set it to nil
+    ///
     /// Make sure you call this method on the same thread as keepAlive()
     public func invalidate() {
         kaTimer?.invalidate()
         kaTimer = nil
     }
+
+    /// lazy name for invalidate() to clear timer
+    ///
+    /// Make sure you call this method on the same thread as keepAlive()
+    public func clearTimer() {
+        invalidate()
+    }
 
     /// Only used in unit tests for now.
     func cleanup() {

TelloSwiftTests/MockTelloFlightTests.swift

@@ -47,7 +47,7 @@ class MockTelloFlightTests: XCTestCase {
             e.fulfill()
         }
         wait(for: [e], timeout: 5)
-        tello.invalidate()
+        tello.clearTimer()
         XCTAssertNil(tello.kaTimer)
     }
 

TelloVideoDecoder/.gitignore

@@ -0,0 +1,68 @@
+# Xcode
+#
+# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
+
+## Build generated
+build/
+DerivedData/
+
+## Various settings
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+xcuserdata/
+
+## Other
+*.moved-aside
+*.xccheckout
+*.xcscmblueprint
+
+## Obj-C/Swift specific
+*.hmap
+*.ipa
+*.dSYM.zip
+*.dSYM
+
+## Playgrounds
+timeline.xctimeline
+playground.xcworkspace
+
+# Swift Package Manager
+#
+# Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
+Packages/
+Package.pins
+Package.resolved
+.build/
+
+# CocoaPods
+#
+# We recommend against adding the Pods directory to your .gitignore. However
+# you should judge for yourself, the pros and cons are mentioned at:
+# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
+#
+# Pods/
+
+# Carthage
+#
+# Add this line if you want to avoid checking in source code from Carthage dependencies.
+# Carthage/Checkouts
+
+Carthage/Build
+
+# fastlane
+#
+# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
+# screenshots whenever they are needed.
+# For more information about the recommended setup visit:
+# https://docs.fastlane.tools/best-practices/source-control/#source-control
+
+fastlane/report.xml
+fastlane/Preview.html
+fastlane/screenshots/**/*.png
+fastlane/test_output

TelloVideoDecoder/README.md

@@ -0,0 +1,61 @@
+# TelloVideoH264Decoder
+This contains a demo macOS app to illustrate how to use the `TelloVideoH264Decoder`
+
+The `TelloVideoH264Decoder` serves like a demo decoder that can meet common requirement
+
+I'm no expert on video decoding and I merely assemble code from different places and make it work. It could be a little buggy, and not world-class flexible for some configurations (e.g. `decodeFlags`) 
+
+Therefore I will be grateful that if you can send me pull requests to make it better. 
+
+## Get a valid NAL Unit
+You need to first generate valid NALU either by yourself or by `getNalUnits()`/ `readNalUnits()`.
+
+>getNalUnits(streamBuffer: Array<UInt8>) -> NALUnit?
+
+will get all valid NALU and abandon incomplete NALU (data before next start code)
+
+>readNalUnits(streamBuffer:inout Array<UInt8>) -> NALUnit?
+
+will consume `streamBuffer`. To stop reading, call `stopProcessing()`
+
+## Get CMSampleBuffer from NALU
+Get a CMSampleBuffer by `getCMSampleBuffer(from nalu: NALUnit)`
+
+## Get CVImageBuffer from CMSampleBuffer
+Get a `CVImageBuffer` by calling `decompress()`
+
+>decompress(sampleBuffer: CMSampleBuffer, outputHandler: @escaping VTDecompressionOutputHandler) -> OSStatus
+
+This is a wrapper of `VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:infoFlagsOut:outputHandler:)`
+
+note that
+>outputHandler cannot be called with a session created with a VTDecompressionOutputCallbackRecord.
+
+### what if I want to use VTDecompressionOutputCallbackRecord?
+Grab the source code and modify `createVTDecompressionSession()` by commenting back 
+```swift
+var outputCallback = VTDecompressionOutputCallbackRecord()
+outputCallback.decompressionOutputCallback = decodeFrameCallback
+outputCallback.decompressionOutputRefCon = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())
+```
+and pass to `outputCallback: ` in `VTDecompressionSessionCreate()`
+
+## About CMSampleTimingInfo
+I don't quite understand what each parameter means while creating the CMSampleTimingInfo. Even if I don't set it, the video streaming seems working well. Welcome any improvement and knowledge sharing.
+
+## About renderVideoStream()
+>renderVideoStream(streamBuffer: inout Array<UInt8>, to videoLayer: AVSampleBufferDisplayLayer)
+
+This is a lazy method for people just want to display the video stream from Tello with  `AVSampleBufferDisplayLayer`
+
+It simply keeps consuming `streamBuffer`, so you would want to put it into a `DispatchQueue` as it will block current thread, and be careful not causing write/read corruption. This also applies to `readNalUnits()`. 
+
+## TelloVideoDecoderMac
+This mac app contains similar code used in `TelloVideoH264Decoder`, just to demonstrate how to use it in different ways.
+
+`startHandling()` behaves like `renderVideoStream()`. You only need one of them in `viewDidAppear()`.
+
+Remember "get a valid NALU" is the first step, so `getNALUnit()` is similar to `getNalUnits()`/ `readNalUnits()`.
+
+## One more thing
+For more information, refer WWDC 2014 Session 513 "Direct Access to Video Encoding and Decoding"