80 lines
2.7 KiB
Markdown
80 lines
2.7 KiB
Markdown
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<!-- cursor Session 966aaa8a-d0b2-4ee4-ad61-ce50447f3408 (2025-11-19 10:02Z) -->
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# PowerShell command version discussion (2025-11-19 10:02Z)
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_**User (2025-11-19 09:43Z)**_
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@pwsh (5-29)
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---
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_**Agent (model default, mode Agent)**_
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<think><details><summary>Thought Process</summary>
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**Explaining ffmpeg scaling expression issue**</details></think>
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---
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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:
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```
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ffmpeg -i rainypet.gif -vf "scale='if(gt(iw,1024),1024,iw)':'if(gt(ih,1024),1024,ih)'" -fs 1M rainypet4.gif
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```
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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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---
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_**User (2025-11-19 09:43Z)**_
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needs transparency
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---
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_**Agent (model default, mode Agent)**_
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<think><details><summary>Thought Process</summary>
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**Considering GIF scaling with transparency**</details></think>
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---
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Use a two-pass palette workflow so ffmpeg keeps the alpha channel:
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```
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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
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```
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- `split` lets one branch create the palette while the other applies it.
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- `paletteuse` re-applies the palette with transparency preserved.
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- `-fs 1M` still enforces the 1 MB cap.
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Run that and the new GIF will stay ≤1024 px on each side and keep its transparent pixels.
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---
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_**User (2025-11-19 09:43Z)**_
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why did it speed it up?
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---
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_**Agent (model default, mode Agent)**_
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<think><details><summary>Thought Process</summary>
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**Explaining frame rate impact from scaling**</details></think>
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---
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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:
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```
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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
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```
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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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---
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