Yalantis/uCrop · error · CImgIOException

load_video(): File '%s', no video reader slots available. Yo

Error message

load_video(): File '%s', no video reader slots available. You have to release some of your previously opened videos.

What it means

CImg keeps a fixed-size pool of OpenCV cv::VideoCapture slots (internal captures[]/filenames[] arrays) for load_video(). This CImgIOException is thrown under mutex 9 when every slot is occupied and a new filename must be opened, i.e. no empty slot exists to host a new video reader.

Source

Thrown at ucrop/src/main/jni/CImg.h:67370

                       "load_video() : File '%s', no opened video stream associated with filename found.",
                       cimglist_instance,filename);
          else
            cimg::warn(_cimglist_instance
                       "load_video() : No opened video stream found.",
                       cimglist_instance,filename);
        if (!step_frame) return *this;
      }

      // Find empty slot for capturing video stream.
      if (index<0) {
        if (!filename)
          throw CImgArgumentException(_cimglist_instance
                                      "load_video(): No already open video reader found. You must specify a "
                                      "non-(null) filename argument for the first call.",
                                      cimglist_instance);
        else { cimg::mutex(9); cimglist_for(filenames,l) if (!filenames[l]) { index = l; break; } cimg::mutex(9,0); }
        if (index<0)
          throw CImgIOException(_cimglist_instance
                                "load_video(): File '%s', no video reader slots available. "
                                "You have to release some of your previously opened videos.",
                                cimglist_instance,filename);
        cimg::mutex(9);
        captures[index] = new cv::VideoCapture(filename);
        positions[index] = 0;
        if (!captures[index]->isOpened()) {
          delete captures[index];
          captures[index] = 0;
          cimg::mutex(9,0);
          cimg::fclose(cimg::fopen(filename,"rb")); // Check file availability
          throw CImgIOException(_cimglist_instance
                                "load_video(): File '%s', unable to detect format of video file.",
                                cimglist_instance,filename);
        }
        CImg<charT>::string(filename).move_to(filenames[index]);
        cimg::mutex(9,0);
      }

View on GitHub (pinned to f788b534b4)

Solutions

Release previously opened videos: assign an empty list (list.assign()) or destroy the CImgList instances holding open captures so their slots free up.
Process videos sequentially, closing/destroying each CImgList before opening the next file.
Raise the pool limit by increasing the internal cimg list of capture slots (recompile with a larger captures array) if many concurrent videos are truly required.

Example fix

// before
for (const char* f : files) {
  list.load_video(f); // slots exhaust after N videos -> throws
}

// after
for (const char* f : files) {
  CImgList<unsigned char> list; // fresh instance per file
  list.load_video(f);
  // ... process ...
} // destructor releases the capture slot

Defensive patterns

Strategy: try-catch

Validate before calling

// track open videos yourself and release before opening new ones
if (openVideoCount >= maxSlots) {
  releaseOldestVideo(); // assign() empty list / destroy instance
}

Try / catch

try {
  list.load_video(filename);
} catch (CImgIOException&) {
  list.assign(); // release slots
  list.load_video(filename); // retry
}

Prevention

Destroy or assign() empty every CImgList used for video loading before opening the next file.
Scope each video load in its own block so destructors free capture slots.
Never accumulate long-lived CImgLists of videos in a loop.

When it happens

Trigger: Calling load_video() with a new filename while all internal video-reader slots are already taken by previously opened videos that were never released.

Common situations: Batch-processing many video files by repeatedly calling load_video() with different filenames on the same CImgList instance without closing/releasing readers; long-running apps (like an Android image-crop pipeline) leaking capture slots.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/d2ed14cd532809ba. Report an issue: GitHub.