Yalantis/uCrop · error · CImgIOException

save_video(): File '%s', no video writer slots available. Yo

Error message

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

What it means

save_video() keeps a fixed-size pool of concurrent cv::VideoWriter slots. When a new filename is given but every slot is occupied by an unreleased video, this IO exception is thrown telling you to release previously opened videos.

Source

Thrown at ucrop/src/main/jni/CImg.h:68574

        if (filename) {
          if (last_used_index>=0 && !std::strcmp(filename,filenames[last_used_index])) {
            index = last_used_index;
          } else cimglist_for(filenames,l) if (filenames[l] && !std::strcmp(filename,filenames[l])) {
              index = l; break;
            }
        } else index = last_used_index;
        cimg::mutex(9,0);

        // Find empty slot for capturing video stream.
        if (index<0) {
          if (!filename)
            throw CImgArgumentException(_cimglist_instance
                                        "save_video(): No already open video writer 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
                                  "save_video(): File '%s', no video writer slots available. "
                                  "You have to release some of your previously opened videos.",
                                  cimglist_instance,filename);
          if (is_empty())
            throw CImgInstanceException(_cimglist_instance
                                        "save_video(): Instance list is empty.",
                                        cimglist_instance);
          const unsigned int W = _data?_data[0]._width:0, H = _data?_data[0]._height:0;
          if (!W || !H)
            throw CImgInstanceException(_cimglist_instance
                                        "save_video(): Frame [0] is an empty image.",
                                        cimglist_instance);
          const char
            *const _codec = codec && *codec?codec:"h264",
            codec0 = cimg::uppercase(_codec[0]),
            codec1 = _codec[0]?cimg::uppercase(_codec[1]):0,
            codec2 = _codec[1]?cimg::uppercase(_codec[2]):0,
            codec3 = _codec[2]?cimg::uppercase(_codec[3]):0;

View on GitHub (pinned to f788b534b4)

Solutions

1. Call close_save_video() (or pass filename and let slots free) for videos you no longer write
2. Reduce the number of simultaneously open video outputs
3. Reuse one output file instead of opening a new writer per segment
4. Audit code paths for missing close_save_video() on error exits

Example fix

// before
for (cam : cams) frames_of(cam).save_video(name(cam)); // slots exhausted
// after
for (cam : cams) { frames_of(cam).save_video(name(cam)); frames_of(cam).close_save_video(); }

// C++
if (openVideoCount() >= kMaxWriters) close_oldest_video();

try { frames.save_video(fname, fps, codec); }
catch (CImgIOException& e) { frames.close_save_video(); frames.save_video(fname, fps, codec); }

When it happens

Trigger: Calling save_video() with a filename when writers[] has no free slot: more videos simultaneously open via save_video() than the pool size allows, without intervening close_save_video() calls.

Common situations: Long-running capture loops opening a new output file per camera/recording without closing finished ones; leaks of cv::VideoWriter slots across threads sharing mutex 9.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• load_video(): File '%s', no video reader slots available. Yo
• load_video() : File '%s', arguments 'first_frame', 'last_fra
• load_video(): No already open video reader found. You must s
• load_video(): File '%s', unable to detect format of video fi
• load_video(): File '%s', unable to locate frame %u.

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/83fefbfc8e22171b. Report an issue: GitHub.