fix: enforce bitrate as a real maximum on Android and iOS/macOS#173
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- Added `getVideoBitrate` method in `MediaInfoExtractor` to probe video bitrate. - Updated integration tests to verify bitrate cap enforcement for compliant and over-cap sources. - Introduced `BitrateCapPolicy` to determine when to force re-encoding based on requested bitrate cap. - Created `BitrateCappedExporter` to handle video rendering with enforced bitrate limits. - Enhanced documentation to clarify bitrate cap behavior and verification steps. - Updated version to 2.4.0 to reflect new features and improvements.
hm21
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…arity and functionality
…e across platforms
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Description
VideoQualityConfig.bitratewas documented as a quality setting but was silently ignored on a no-edit export: Android transmuxed the source untouched (an ~18 Mbit/s camera clip stayed ~18 Mbit/s despite an 8 Mbit/s request), and iOS/macOS mapped the value to the nearestAVAssetExportSessionpreset, which chooses its own bitrate (10–16 Mbit/s at 1080p). This makesbitratea guaranteed maximum on all three platforms.cap × 1.2(tolerance) and nothing else forces a re-encode, keep the lossless transmux fast path; otherwise force the Media3 video track throughResilientVideoEncoderFactoryso the bitrate is actually applied. The decision is factored into a unit-testedBitrateCapPolicyand evaluated against the final (post pre-transcode/reverse/transition) clip paths.AVAssetExportSessionrender with anAVAssetReader→AVAssetWriterpipeline that setsAVVideoAverageBitRateKey(reusing theStopMotionGeneratorpattern), preserving the video composition (filters/blur/layers/transitions), audio mix, global trim, frame-rate cap, progress and cancellation. A compliant no-edit source is remuxed losslessly viaAVAssetExportPresetPassthrough.bitrate == null: behavior unchanged.shouldOptimizeForNetworkUse(moov-at-front) works on both the fast and re-encode paths.Note: an over-cap source that used to export losslessly is now re-encoded down to the cap.
Verification
moov-at-front honored on both paths.bitrate_cap_test.dartpasses on macOS and a Galaxy S942B (Android 16); the fullvideo_render_test.dartregression suite passes on both (macOS 78, Android 71 + 8 platform-skipped).BitrateCapPolicytests; iOS builds clean;flutter analyze+ 251 Dart unit tests pass.example/docs/bitrate_cap_verification.md.Related Issue: Closes #
Type of Change