Fix busy-wait that stalled video writing under CI load - #11
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The requestMediaDataWhenReady block had two problems that could leave the build hanging until the test timeout: 1. It wrapped the append loop in an outer while-loop over the remaining assets, so when the input's buffer filled (isReadyForMoreMediaData became false) it busy-spun on the media queue, starving the encoder. 2. Finalization (markAsFinished/finishWriting) happened only inside the 'is ready' loop. If appending the final frame filled the input's buffer, the loop exited before finalizing and the writer waited on a readiness callback that never needed to come — an intermittent stall that timed out the multi-frame test. Follow AVFoundation's documented pattern: append while the input is ready, return when it is not so the block is re-invoked, and finalize once the queue is empty regardless of readiness (markAsFinished does not require a ready input). State that must survive re-invocation lives outside the block.
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The first AVAssetWriter/H.264 use on the CI simulator pays a large, variable cold-start cost (30s+ observed), which landed inside the first video test's timed expectation and could trip its timeout. Pay that cost once in setUp, outside any XCTest expectation, so each test only measures steady-state latency.
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This fixes a race condition that stalled CI and could have caused on-device delays, too. When the writer input's buffer filled (
isReadyForMoreMediaDatareturns), the block kept spinning on the media queue instead of returning, which then starved the encoder threads. The updated code better conforms to the pattern that Apple recommends.