| name | video-streaming |
| description | Stream video to mobile with HLS/DASH adaptive bitrate and optional DRM. Use when building or integrating a video delivery pipeline for a mobile app. |
Video Streaming for Mobile
Instructions
Mobile video requires adaptive bitrate (ABR) streaming -- the client switches between renditions based on bandwidth. Serve HLS on iOS (mandatory) and HLS or DASH on Android (HLS is simplest cross-platform).
1. Packaging
Source file -> transcoded into multiple renditions -> packaged as HLS/DASH -> stored on object storage -> served through a CDN.
Renditions for UGC-style content (rules of thumb):
| Resolution | Bitrate (video) | Audio |
|---|
| 240p | 250 kbps | 64 kbps |
| 360p | 500 kbps | 64 kbps |
| 480p | 1.0 Mbps | 96 kbps |
| 720p | 2.5 Mbps | 128 kbps |
| 1080p | 4.5 Mbps | 128 kbps |
- Codec: H.264 (wide compatibility) + HEVC or AV1 for newer devices.
- Segment length: 4–6 seconds; shorter (2 s) only for low-latency HLS.
- Keyframe-aligned segments across renditions so the player can switch cleanly.
2. Pipeline
upload -> transcode worker (ffmpeg / AWS MediaConvert / Mux) -> HLS/DASH output
-> object storage (media/<id>/hls/master.m3u8, media/<id>/hls/720p/*.ts)
-> CDN
ffmpeg one-shot HLS (simplified):
ffmpeg -i input.mp4 \
-filter_complex "[0:v]split=3[v1][v2][v3]; \
[v1]scale=w=854:h=480[v1out]; \
[v2]scale=w=1280:h=720[v2out]; \
[v3]scale=w=1920:h=1080[v3out]" \
-map "[v1out]" -c:v:0 libx264 -b:v:0 1000k \
-map "[v2out]" -c:v:1 libx264 -b:v:1 2500k \
-map "[v3out]" -c:v:2 libx264 -b:v:2 4500k \
-map a:0 -map a:0 -map a:0 -c:a aac -b:a 128k \
-var_stream_map "v:0,a:0 v:1,a:1 v:2,a:2" \
-f hls -hls_time 4 -hls_playlist_type vod \
-master_pl_name master.m3u8 \
-hls_segment_filename "out/%v/seg_%03d.ts" "out/%v/index.m3u8"
For production, a managed service (AWS MediaConvert, Google Transcoder API, Mux, Bitmovin) saves a huge amount of ops work.
3. CMAF and fMP4
Prefer CMAF (fragmented MP4) segments. The same fMP4 files serve both HLS and DASH manifests; you halve storage and invalidation overhead. Required for low-latency HLS and for Widevine + FairPlay + PlayReady shared DRM.
4. Low-Latency HLS (LL-HLS)
Needed for live/near-live use cases (sub-5 s). Requires partial segments, blocking playlist reload, and CDN support. Most VoD apps do not need this; live-ish apps (sports, auctions, collab) do.
5. Adaptive Bitrate Clients
iOS (AVPlayer): HLS is native; set AVPlayerItem.preferredPeakBitRate to cap on cellular:
let asset = AVURLAsset(url: URL(string: "https://cdn/media/\(id)/hls/master.m3u8")!)
let item = AVPlayerItem(asset: asset)
if networkMonitor.isCellular { item.preferredPeakBitRate = 1_500_000 }
let player = AVPlayer(playerItem: item)
Android: ExoPlayer supports HLS and DASH:
val player = ExoPlayer.Builder(context).build()
val source = HlsMediaSource.Factory(DefaultHttpDataSource.Factory())
.createMediaSource(MediaItem.fromUri("https://cdn/media/$id/hls/master.m3u8"))
player.setMediaSource(source)
player.prepare()
For Flutter / React Native, wrap the native players; do not roll your own.
6. DRM
Two tiers:
- AES-128 HLS encryption (signed key URL). Low-friction, blocks casual piracy. Not studio-grade.
- Widevine (Android) + FairPlay (iOS) + PlayReady (others) via a license server (AWS, DRMtoday, EZDRM, Axinom). Required for premium content and most licensed VOD.
CMAF + CENC + multi-DRM lets one set of files serve both. License exchange happens between the player and the license server; your backend signs a short-lived license request token.
7. Access Control
- Signed manifest URLs (CloudFront signed cookies or tokenized URLs) so the playlist is not guessable.
- Token bound to
user_id + video_id + TTL.
- Segment URLs inherit the same signature (CDN path-based).
- Enforce geo / age / subscription checks at token-mint time, not in-flight.
8. Subtitles and Audio Tracks
- WebVTT sidecars referenced in the master playlist.
- Multi-language audio renditions flagged with
LANGUAGE tags.
- Support forced captions for foreign-language segments.
9. Analytics
- QoE metrics: startup time, rebuffer ratio, average bitrate, error rates.
- Use CMCD (Common Media Client Data) headers so CDN logs carry player state.
- Alert on rebuffer ratio > 1% sustained -- likely a bitrate ladder or CDN issue.
10. Edge Cases
- iOS requires HLS for cellular-backed video playback in App Store policy; plan accordingly.
- Background audio: iOS needs
audio background mode; the manifest must allow extraction.
- PiP: supported via native APIs; test with your chosen DRM.
- Chromecast / AirPlay: ensure the CDN URLs are reachable from the cast target (some DRM + signed cookies do not play well here).
Checklist
