2020-08-13-rainynew/rainypet/.specstory/history/2025-11-19_10-02Z-powershell-command-version-discussion.md

PowerShell command version discussion (2025-11-19 10:02Z)

User (2025-11-19 09:43Z)

@pwsh (5-29)

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Agent (model default, mode Agent)

Thought Process

Explaining ffmpeg scaling expression issue

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min() only accepts two inputs, so nesting three values in one call makes the filter expression invalid. A cleaner way to cap the GIF at 1024 px on either axis while preserving aspect ratio is to compare the dimensions to 1024 explicitly:

ffmpeg -i rainypet.gif -vf "scale='if(gt(iw,1024),1024,iw)':'if(gt(ih,1024),1024,ih)'" -fs 1M rainypet4.gif

This tells ffmpeg to use 1024 whenever a dimension exceeds that limit, otherwise keep the original value, so you avoid the parse error and still constrain the size.

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User (2025-11-19 09:43Z)

needs transparency

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Agent (model default, mode Agent)

Thought Process

Considering GIF scaling with transparency

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Use a two-pass palette workflow so ffmpeg keeps the alpha channel:

ffmpeg -i rainypet.gif -vf "scale='if(gt(iw,1024),1024,iw)':'if(gt(ih,1024),1024,ih)',split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" -fs 1M rainypet4.gif

• split lets one branch create the palette while the other applies it.
• paletteuse re-applies the palette with transparency preserved.
• -fs 1M still enforces the 1 MB cap.

Run that and the new GIF will stay ≤1024 px on each side and keep its transparent pixels.

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User (2025-11-19 09:43Z)

why did it speed it up?

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Agent (model default, mode Agent)

Thought Process

Explaining frame rate impact from scaling

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GIF frame timing is stored as per-frame delays, not a global FPS. When ffmpeg filters the frames (scale + split + palettegen/paletteuse), it often rewrites the stream from scratch. If the sample delays in the source were unusual—e.g., some frames at 2 cs (50 fps) and others longer—ffmpeg may normalize them to the default 1 cs (100 fps) or simply round everything to 2 cs, making the animation feel faster. You can lock the intended timing by explicitly telling ffmpeg what delay you want:

ffmpeg -i rainypet.gif -filter_complex "scale='if(gt(iw,1024),1024,iw)':'if(gt(ih,1024),1024,ih)',split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse,setpts=N/50/TB" -fs 1M rainypet4.gif

Adjust the divisor in setpts=N/50/TB to match the real frame rate (50 here). If the original GIF used a different cadence, replace 50 with the actual fps or compute it from the original delays.

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