{"record":{"id":"fcab1ac2873a066f","repo":"Yalantis/uCrop","slug":"save-video-file-s-unable-to-initialize-vide","errorCode":null,"errorMessage":"save_video(): File '%s', unable to initialize video writer with codec '%c%c%c%c'.","messagePattern":"save_video\\(\\): File '(.+?)', unable to initialize video writer with codec '%c%c%c%c'\\.","errorType":"exception","errorClass":"CImgIOException","httpStatus":null,"severity":"error","filePath":"ucrop/src/main/jni/CImg.h","lineNumber":68599,"sourceCode":"                                        cimglist_instance);\n          const unsigned int W = _data?_data[0]._width:0, H = _data?_data[0]._height:0;\n          if (!W || !H)\n            throw CImgInstanceException(_cimglist_instance\n                                        \"save_video(): Frame [0] is an empty image.\",\n                                        cimglist_instance);\n          const char\n            *const _codec = codec && *codec?codec:\"h264\",\n            codec0 = cimg::uppercase(_codec[0]),\n            codec1 = _codec[0]?cimg::uppercase(_codec[1]):0,\n            codec2 = _codec[1]?cimg::uppercase(_codec[2]):0,\n            codec3 = _codec[2]?cimg::uppercase(_codec[3]):0;\n          cimg::mutex(9);\n          writers[index] = new cv::VideoWriter(filename,_cimg_fourcc(codec0,codec1,codec2,codec3),fps,cv::Size(W,H));\n          if (!writers[index]->isOpened()) {\n            delete writers[index];\n            writers[index] = 0;\n            cimg::mutex(9,0);\n            throw CImgIOException(_cimglist_instance\n                                  \"save_video(): File '%s', unable to initialize video writer with codec '%c%c%c%c'.\",\n                                  cimglist_instance,filename,\n                                  codec0,codec1,codec2,codec3);\n          }\n          CImg<charT>::string(filename).move_to(filenames[index]);\n          sizes(index,0) = W;\n          sizes(index,1) = H;\n          cimg::mutex(9,0);\n        }\n\n        if (!is_empty()) {\n          const unsigned int W = sizes(index,0), H = sizes(index,1);\n          cimg::mutex(9);\n          cimglist_for(*this,l) {\n            CImg<T> &src = _data[l];\n            if (src.is_empty())\n              cimg::warn(_cimglist_instance\n                         \"save_video(): Skip empty frame %d for file '%s'.\",","sourceCodeStart":68581,"sourceCodeEnd":68617,"githubUrl":"https://github.com/Yalantis/uCrop/blob/f788b534b48c144edf786c8cddbf0e029e637804/ucrop/src/main/jni/CImg.h#L68581-L68617","documentation":"After constructing cv::VideoWriter with the requested codec fourcc, fps and frame size, save_video() checks isOpened(). OpenCV failing to open the writer causes this IO exception listing the filename and codec characters.","triggerScenarios":"cv::VideoWriter cannot open: unsupported codec fourcc for the extension (e.g. 'h264' without OpenH264/ffmpeg backend), invalid fps, unsupported resolution, unwritable/invalid output path, or missing OpenCV video backend.","commonSituations":"Using 'h264' codec with a stock OpenCV build lacking H264 encoder support; mismatched extension/codec (e.g. .avi with mp4v unavailable); fps of 0; target directory missing.","solutions":["Use a codec the OpenCV backend supports (e.g. 'mp4v' with .mp4, 'MJPG' with .avi) or install OpenH264/ffmpeg for h264","Verify the output directory exists and is writable","Check fps>0 and that WxH match the actual frame size","Test writing a tiny video with cv::VideoWriter directly to isolate backend issues"],"exampleFix":"// before\nframes.save_video(\"out.mp4\", 25, \"h264\"); // fails without H264 encoder\n// after\nframes.save_video(\"out.mp4\", 25, \"mp4v\"); // widely supported fourcc","handlingStrategy":"fallback","validationCode":"// C++\nstd::string ext = extension_of(fname);\nbool okPair = (codec == \"mp4v\" && ext == \".mp4\") || (codec == \"MJPG\" && ext == \".avi\");\nif (!okPair) codec = defaultCodecFor(ext);","typeGuard":null,"tryCatchPattern":"try { frames.save_video(fname, fps, \"h264\"); }\ncatch (CImgIOException& e) { frames.save_video(fname, fps, \"mp4v\"); }","preventionTips":["Use fourcc/extension combos known to work (MJPG+.avi, mp4v+.mp4)","Ensure the OpenCV build has a video backend and H264 support if needed","Pass fps>0 and correct WxH","Test writer initialization once at app startup"],"tags":["video","opencv","codec","unsupported-codec"],"backgroundTag":"unsupported-operation","analyzedSha":"f788b534b48c144edf786c8cddbf0e029e637804","analyzedAt":"2026-09-08T08:36:04.887Z","contentChangedAt":"2026-09-08T08:36:04.887Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}