We specialize in developing video publication for mobile apps. A typical problem: a user records 4K/60fps video—400 MB for 60 seconds. Sending such a file to the server without processing makes upload last minutes, and the feed player will lag. Savings on traffic when transcoding can reach $500 monthly per 1000 posts. The solution—transcoding, trimming, and resumable upload. Below is how to do it on iOS and Android with best practices. Our experience: over 5 years in mobile development, over 20 projects with video content. If you need such a feature, contact us for a consultation.
Video Picking and Trimming
PHPickerViewController with filter: .videos on iOS. For social posts we typically limit length to 60–90 seconds. We check duration via PHAsset.duration in the picker, before loading data.
Trimming—AVPlayerViewController with built-in trim editor (iOS 14+, AVPlayerViewController.allowedPictureInPictureMediaTypes), or a custom trimmer via AVPlayer + AVPlayerLayer with drag-handles for CMTimeRange. A custom trimmer gives full UI control but requires ~2–3 days of separate development.
On Android—VideoTrimmingView using MediaPlayer + MediaMetadataRetriever for timeline generation. Or we use isoviewer / mp4parser for trimming without full decoding.
Technical details for media picking
On iOS we use `PHPhotoLibrary.requestAuthorization(for: .readWrite)` to access the gallery. On Android—`ActivityResultContracts.GetContent()` with MIME type `video/*`. On both platforms we check size and duration before loading.Mandatory Transcoding
Video from a modern smartphone camera at 4K/60fps—400 MB per minute. For a 60-second post that's 400 MB. We transcode before upload.
Target parameters for posts: 1080p, H.264, 4–6 Mbps, AAC 128 kbps. This yields ~35–45 MB for a 60-second clip—a reasonable compromise between quality and size. Device transcoding takes 20–30 seconds, which is 2–3 times faster than uploading the original to a server and processing it back.
On iOS—AVAssetExportSession with AVAssetExportPreset1920x1080:
let export = AVAssetExportSession(asset: asset, presetName: AVAssetExportPreset1920x1080)! export.outputURL = tempOutputURL export.outputFileType = .mp4 export.exportAsynchronously { // completion } Transcoding progress via export.progress polled with a timer—AVAssetExportSession has no progress delegate, only polling. On iPhone SE 2nd gen, transcoding a 60-second video takes 20–30 seconds. A clear progress indicator is required, otherwise the user might think the app is frozen.
The transcoding process:
- Get the source
AVAsset. - Set output parameters (preset, codec, container).
- Start asynchronous export.
- Track progress via polling.
- Handle errors or use the finished file on completion.
On Android—FFmpegKit for flexible transcoding or MediaTranscoder (Natario1)—a more modern library using MediaCodec without FFmpeg. MediaTranscoder weighs ~500 KB vs ~15 MB for FFmpegKit—a 30x difference, important for APK size.
How to Implement Resumable Upload?
Video for a post is a large file; upload must support resumption. We use S3 Multipart Upload: the file is split into 5–10 MB parts, each uploaded in parallel (2–3 parallel requests speed up upload without overloading the network).
- Split the file into fixed-size parts.
- Parallel upload of parts with error handling.
- Assemble the file on the server.
On iOS—URLSession with BackgroundConfiguration to continue upload on app backgrounding. Completion handler via application(_:handleEventsForBackgroundURLSession:) in AppDelegate.
On Android—WorkManager with UploadWorker and setConstraints(Constraints.Builder().setRequiredNetworkType(CONNECTED).build()). WorkManager guarantees execution even after device restart—if the user left the app mid-upload, on next launch the upload continues.
How to Optimize Preview and Feed Player?
Preview frame is generated before upload—from the original video using AVAssetImageGenerator (iOS) or MediaMetadataRetriever (Android), a frame at the 1st second. Preview is uploaded separately, fast—the user sees the post in the feed with a preview while the video is still processing.
Feed player—autoplay on appearance in viewport. Don't use AVPlayer for each cell—a single shared AVPlayer reassigned on scroll (AVQueuePlayer for preloading next). On Android—ExoPlayer with ExoPlayer.Builder().setLoadControl(DefaultLoadControl()) and PlayerView in RecyclerView. Preload next video on scroll via MediaSource in ConcatenatingMediaSource.
Mute by default—standard for feed autoplay. Sound toggled on tap.
Comparison of Approaches on iOS and Android
| Component | iOS | Android |
|---|---|---|
| Video Picking | PHPickerViewController | ActivityResultContracts.GetContent() |
| Transcoding | AVAssetExportSession | MediaTranscoder (500 KB) vs FFmpegKit (15 MB) |
| Resumable Upload | URLSession BackgroundConfiguration | WorkManager |
| Feed Player | AVQueuePlayer | ExoPlayer |
| Preview Generation | AVAssetImageGenerator | MediaMetadataRetriever |
Timeline and Scope of Work
| Stage | Duration | Notes |
|---|---|---|
| Picking + trimming + transcoding + upload + preview + player | 3–5 days | With existing backend and API |
| Additional: custom trimmer, background upload, optimistic UI | +2–3 days |
Note: what's included: requirements analysis, architecture design, implementation with code review, build and deployment documentation, user instructions, one month post-release support. Development cost for such functionality typically ranges from $6,000 to $12,000 depending on platforms and complexity. Request development and see the quality of our approach.
If you need to implement video posts in your app, write to us—we'll help. Get a consultation on integrating video posts into your app.