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PHPicker Automatic Transcoding Behavior

Overview

When using PHPickerViewController to select videos from the Photos library, iOS automatically transcodes HEVC (H.265) videos to H.264 format by default. This document explains why this happens and how to control it.

Default Behavior

When preferredAssetRepresentationMode is not explicitly set:

• iOS defaults to .automatic mode
• The system assumes maximum compatibility is needed
• HEVC videos are automatically transcoded to H.264
• File sizes reduce significantly (e.g., 11GB HEVC → 4.7GB H.264)
• Transcoding happens during the loadFileRepresentation(forTypeIdentifier:) call

Why Apple Does This

1. Compatibility: Not all apps/systems support HEVC
2. Privacy: The picker runs in a separate process and provides a “safe” version
3. User Experience: Prevents app crashes from unsupported formats

PHPickerConfigurationAssetRepresentationMode Options

.automatic (Default)

• System chooses the most appropriate representation
• Typically transcodes HEVC → H.264 for compatibility
• Results in smaller file sizes but takes time to transcode

.current

• Uses current representation and avoids transcoding, if possible
• Preserves original HEVC format and quality
• Larger file sizes (original format)
• Faster export (no transcoding overhead)

.compatible

• Uses the most compatible representation
• Forces transcoding to ensure compatibility
• Similar behavior to .automatic but more explicit

Implementation in This App

// Current implementation (PickerBridges.swift, line 13-15)
var config = PHPickerConfiguration()
config.filter = .videos
config.selectionLimit = 1
// preferredAssetRepresentationMode NOT set = defaults to .automatic
// Result: HEVC videos are transcoded to H.264

To preserve original HEVC format:

var config = PHPickerConfiguration()
config.filter = .videos
config.selectionLimit = 1
config.preferredAssetRepresentationMode = .current  // Preserve HEVC

Trade-offs

Using Default (.automatic) - Current Approach

Pros:

• Smaller file sizes (~60% reduction)
• Better compatibility (H.264 works everywhere)
• More likely to fit within upload size limits

Cons:

• Transcoding takes time during file copy
• Quality loss from re-encoding
• User sees “Preparing…” progress indicator

Using .current

Pros:

• Preserves original quality
• Faster export (no transcoding)
• Original codec maintained

Cons:

• Much larger file sizes (may exceed 6GB limit)
• HEVC may not be compatible with all systems
• Requires more storage space

Apple Documentation Sources

1. PHPickerConfiguration API Reference
   • https://developer.apple.com/documentation/photokit/phpickerconfiguration
2. PHPickerConfigurationAssetRepresentationMode Enum
   • https://developer.apple.com/documentation/photokit/phpickerconfigurationassetrepresentationmode
3. WWDC 2020 Session 10652: “Meet the new Photos picker”
   • https://developer.apple.com/videos/play/wwdc2020/10652/
4. Apple Developer Forums - Key Quote from Apple Engineer:

   “Unless .current is specified, transcoding can happen if your app doesn’t support the original file format. For example, if your app can only support JPEG but the original image is stored as HEIF, the system will transcode the image to JPEG for you.”

   • https://developer.apple.com/forums/thread/736545

Observed Behavior in This App

• Original video: 24 minutes, HEVC, 11GB (as shown in Photos app)
• After PHPicker export: H.264, 4.7GB, .mov container
• Codec details (from ffprobe):
  • Video: h264 (High), 3840x2160, 24,956 kb/s, 30 fps
  • Audio: aac (LC), 44100 Hz, stereo, 184 kb/s
  • Container: QuickTime (.mov)

Recommendation

Keep current default behavior (automatic transcoding) because:

1. Smaller file sizes make uploads more feasible
2. H.264 has universal compatibility
3. Files are more likely to stay under the 6GB upload limit
4. Chrome and other browsers handle H.264 better

If users need original quality, they should use the Files app picker instead of Photos picker, or we could add a settings toggle to enable .current mode.

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Change Default Video Encoding on iPhone (H.264 vs HEVC)

Yes — it is possible to set your iPhone to record videos using H.264 (Most Compatible) instead of HEVC (High Efficiency). Here’s how to do it:

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🎥 Steps to Change the Default Encoding

1. Open ⚙️ Settings
2. Scroll down and tap Camera
3. Tap Formats
4. Under Camera Capture, choose:
   • ✅ Most Compatible → uses H.264 for videos and JPEG for photos
   • High Efficiency → uses HEVC (H.265) for videos and HEIF for photos

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⚙️ What Happens When You Choose “Most Compatible”

• New videos you record will use H.264 (.MOV) encoding.
• File sizes will be larger, but compatibility improves with:
  • Older Macs and PCs
  • Web browsers
  • Video editing software that doesn’t support HEVC natively

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⚠️ Notes

• HEVC (High Efficiency) is on by default on newer iPhones (like iPhone 15, 15 Pro, and upcoming M4 models).
• H.264 takes more storage space — expect roughly 2× larger files.
• The setting affects new captures only — existing HEVC videos remain in that format.

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📦 Optional: Converting Existing HEVC Videos to H.264

If you want to convert older HEVC videos to H.264 for compatibility:

On macOS (using QuickTime Player)

1. Open the video in QuickTime.
2. Choose File → Export As → [resolution].
3. Pick “Greater Compatibility (H.264)” when prompted.

On the Command Line (using ffmpeg)

ffmpeg -i input.mov -c:v libx264 -c:a aac output_h264.mov

This command re-encodes the video using H.264 and AAC for audio.