Editing Movies in AV Foundation.md

Editing Movies in AV Foundation

@ WWDC 15

AVAsset and Its Edting Subclasses

AVAsset > AVComposition > AVMutableComposition

AVAsset > AVMovie > AVMutableMovie

AVAssetTrack and Its Subclasses

AVAssetTrack > AVCompositionTrack > AVMutableCompositionTrack

AVMovieTrackc > AVMutableMovieTrack

New Movie Editing Classes

• AVMoviee, AVMutableMovie
• AVMovieTrack, AVMutableMovieTrack
• AVMediaDataStorage

QuickTime Movie Files

• A Sequence of boxes (<- box라는 표현을 사용해서 데이터들을 표현하더랑)

• File Type / Unused / Movie / Sample Data

Movie Box

그 중에서도 Movie Box는 global settings, metadata, track information을 가짐

Global Settings	Movie Metadata	Track Boxes
Track count, duration, creation date, preferred rate	Copyright statement, Author, titlle, custom metadata	Track type, sample data location, track metadata, track associations

Track Box

트랙 박스는 샘플 데이터를 참조해서 트랙으로 정리한다. (Sample references) 또, 외부 샘플 데이터를 가리킬 수도 있다.

Sample Reference Movie Files

• Provide a powerful workflow tool
• But sample reference movies are inherently fragile
• To help reduce that fragility, use relative URLs
• When it's time to deliver content, export it using AVAssetExportSession

AVMovie

• AVMovie provides inspection and header-writing methods

  • Get a list of tracks in th movie
  • Retrieve the movie header from an existing file
  • Write a movie header into a new file

• let movie = AVMovie(URL: inputURL, options: nil)

• let movie = AVMovie(data: inputData, options: nil)

• Create a sample reference movie file

  let movies = AVMovie(URL: inputURL, options: nil)
  let options = AVMovieWritingOptions.TruncateDestinationToMovieHeaderOnly
  
  try movie.writeMovieHeaderToURL(outputURL, fileType: AVFileTypeQuickTimeMovie, options: options)

AVMutableMovie

• AVMutableMovie adds editing methods:

  • Perform range-based track editing
  • Set track associations between tracks
  • Add or modify track metadata

• func removeTimeRange(timeRange: CMTimeRange)

• func insertEmptyTimeRange(timeRange: CMTimeRange)

• func scaleTimeRange(timeRange: CMTimeRange, toDuration: CMTime)

• func insertTimeRange(timeRange, CMTimeRange, ofTrack: AVAssetTrack, atTiime: CMTime, copySampleData: Bool) throws

• Setting the container for a track's new sample data

  track.mediaDataStorage = AVMediaDataStorage(URL: movURL, options: nil)

AVMutableMovieTrack

• func addTrackAssociationToTrack(movieTrack: AVMovieTrack, type: String)

• func removeTrackAssociatioinToTrack(movieTrack: AVMovieTrack, type: String)

• Use case: using relative URLs to reference data

  let url = NSURL(fileURLWithPath: "/Users/monroe/tristo_boston/movies")
  
  for track in movies.tracks {
    track.sampleReferenceBaseURL = url
  }

The Task: manage 1.5 terabytes of data

여기서 보여 줄 에제는 1.5 테라의 데이터를 어떻게 다룰 것인지!

• Step 1: Combine each sortie's MPEG-4 fiiles into one sampple reference movie file
• Step 2: Add indexing metadata as movie metadata
• Steep 3: Add GPS data as a timed metadata track

Do this all without modifying the original files and minimizing data copying

Step 1

Combine camera files into a sample reference movie file

let movie = AVMutableMovie(URL: url1, options: nil)
let asset = AVURLAsset(URL: url2, options: nil)

let range = CMTimeRangeMake(kCMTimeZero, asset.duration)

try movie.insertTimeRange(range, ofAsset: asset, atTime: movie.duration, copySampleData: false)

try movie.writeMovieHeaderToURL(dstURL, fileType: AVFileTypeQuickTimeMovie, options: AVMovieWritingOptions.AddMovieHeaderToDestination)

Step 2

Add custom metadata

var metadataArray = movie.metadata

var newItem = AVMutableMetadataItem()
newItem.identifier = "mdta/com.example.weather.wind"
newItm.locale = NSLocale.currentLocale()
newItem.value = averageWindSpedValue
newItem.extraAttributes = nil

metadataArray.append(newItem)
movie.metadata = metadataArray

Step 3

Create a movie file containing location timed metadata

• See "Harnessing Metadata in Audiovisual Media", WWDC 2014
• Sample code: AVCaptureLocation and AVTmedAnnotationWriter

Add a timed metadata track for l!)

let vidTrack = movie.tracksWithMediaTye(AVMediaTypeVideo).first
let type = AVTrackAssociationTypeMetadataReferent

newTrack.addTrackAssociationToTrack(vidTrack, type)

Summary

• New editing features pprovide accss to QuickTime movie file format
• Allows simplified editing workflows, especially when handling large amounts of data
• Sample code: AVMovieEditor