@remotion/renderer: Improved render time estimates

[Copilot]

The renderEstimatedTime calculation in render-media.ts was inaccurate because it used all frame timings to calculate the average render time, causing the first few slow frames to skew the estimation for the entire render.

Problem

The current algorithm:

1. Accumulates time for ALL frames rendered so far in totalTimeSpentOnFrames
2. Calculates average as totalTimeSpentOnFrames / renderedFrames
3. Uses this average to estimate remaining time

This approach is problematic because:

• Initial frames are often slower due to cold start, initialization, etc.
• These slow frames continue to impact the average throughout the entire render
• Time estimates remain pessimistic even as rendering speed stabilizes

Solution

Modified the algorithm to track only the most recent 50 frame timings:

// Track recent frame timings (at most 50)
recentFrameTimings.push(timeToRenderInMilliseconds);
if (recentFrameTimings.length > MAX_RECENT_FRAME_TIMINGS) {
    recentFrameTimings.shift();
}

// Calculate average using only recent timings for better estimation
const recentTimingsSum = recentFrameTimings.reduce((sum, time) => sum + time, 0);
const newAverage = recentTimingsSum / recentFrameTimings.length;

Benefits

• More accurate time estimates that adapt to current rendering performance
• Eliminates bias from slow initial frames
• Provides better user experience with realistic progress indicators
• Maintains backward compatibility (existing totalTimeSpentOnFrames preserved)

Changes

• Added MAX_RECENT_FRAME_TIMINGS = 50 constant
• Added recentFrameTimings: number[] array to track recent frame render times
• Updated estimation calculation to use rolling average of recent timings
• All existing tests pass

Fixes #5462.

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