Gif/APNG/WEBM generation fails

[ricebl]

Describe the bug Clicking either of those 3 Generate options on an Ugoira post causes some console errors related to FFMPEG and the toolkit gets stuck generating until you refresh. Feature used to work just fine, I am unsure when it stopped.

Expected behavior GIF/APNG/WEBM should be generated

Example work from Pixiv Pixiv Post

Screenshots

Browser and Version (please complete the following information): Opera GX, utilizing Chrome extensions

Settings of extension {"MangaPageNumberStartWithOne":false,"alwaysPack":false,"animationJsonFormat":1,"askDownloadSavedWork":true,"autoActivateDownloadPanel":true,"disableDownloadsShelf":false,"displayWorkTypeLabel":true,"downloadPackFiles":true,"downloadPanelPosition":"center","downloadPanelStyle":1,"downloadRelativeLocation":null,"downloadSaveAs":false,"downloadTasksWhenDownloadingImages":3,"enableExtTakeOverDownloads":false,"enableExtend":false,"enableExtension":true,"enablePackUgoiraFramesInfo":true,"enablePtkSearch":true,"enableSaveDownloadHistory":1,"enableSaveVisitHistory":true,"enableWhenUnderSeconds":1,"extendDuration":3,"featureKnown":false,"guideShowed":true,"illustrationCreateSubdirectory":1,"illustrationImageRenameFormat":"{id}{pageNum}","illustrationKeepPageNumber":false,"illustrationPageNumberLength":0,"illustrationPageNumberStartWithOne":false,"illustrationRelativeLocation":"","illustrationRenameFormat":"{authorId}{id}","importantNoticeDisplayed":true,"language":"default","mangaImageRenameFormat":"{id}{pageNum}","mangaPageNumberLength":0,"mangaPagesInChunk":99,"mangaRelativeLocation":"","mangaRenameFormat":"{authorId}{id}","maxDownloadRecords":10000,"maxHistoryItems":10000,"multipleDownloadsGapTime":150,"notSaveNSFWWorkInHistory":false,"novelIncludeDescription":false,"novelRelativeLocation":"","novelRenameFormat":"","pixivComicImageRenameFormat":"{episodeId}_{episodeTitle}p{pageNum}","pixivComicPageNumberLength":0,"pixivComicPageNumberStartWithOne":false,"pixivComicRelativeLocation":"","pixivComicRenameFormat":"{episodeId}{episodeTitle}","showPixivOmina":true,"showReloadInPopup":false,"showUpdateChangeLog":true,"statIllustDownloaded":1705,"statMangaDownloaded":123,"statNovelDownloaded":0,"statUgoiraDownloaded":25,"ugoiraConvertTool":"ffmpeg","ugoiraCustomFFmpegCommand":"","ugoiraQuanlity":10,"ugoiraRelativeLocation":"","ugoiraRenameFormat":"","version":"5.5.3","visitHistoryType":"list","workCoverSize":1}

[ricebl]

Noticed this is only happening when using FFMPEG, with default as the option it doesn't happen.