[video_player] FIX invalid videoComposition crash on iOS

[GiacomoPignoni]

I've added an additional check on the extracted frameDuration to be sure that it's also positive using CMTIME_IS_POSITIVE_INFINITY

Fix flutter/flutter#151031

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[gemini-code-assist]

Code Review

This pull request aims to fix a crash caused by a non-positive frameDuration when creating an AVMutableVideoComposition. The proposed change adds a check using CMTIME_IS_POSITIVE_INFINITY. While this prevents the crash for zero-duration values, it is logically incorrect. This check will fail for any valid, positive frame duration that is not positive infinity, causing the code to fall back to a default frame rate for nearly all videos. I've provided a suggestion to use CMTimeCompare to correctly check if the duration is positive, which fixes the crash while preserving the intended behavior.

[gemini-code-assist]

The use of CMTIME_IS_POSITIVE_INFINITY is incorrect for checking if a CMTime value is positive. This macro specifically checks if the time is positive infinity, not whether it's greater than zero. As a result, for any valid video with a finite frame duration (e.g., 1/30s), this condition will be false, and the code will incorrectly fall back to a default frame duration of 30fps.

The correct way to ensure the frameDuration is positive is to compare it with kCMTimeZero.

Suggested change

	if (CMTIME_IS_VALID(videoTrack.minFrameDuration) && CMTIME_IS_POSITIVE_INFINITY(videoTrack.minFrameDuration)) {
	if (CMTIME_IS_VALID(videoTrack.minFrameDuration) && CMTimeCompare(videoTrack.minFrameDuration, kCMTimeZero) > 0) {