Add multithreading to the OCR

CMakeLists.txt

@@ -54,7 +54,7 @@ include(CheckCXXSourceCompiles)
 include(CheckCXXSourceRuns)
 
 set(CMAKE_C_FLAGS "-std=gnu99")
-set(CMAKE_CXX_FLAGS "-ansi -pedantic -Wall -Wextra -Wno-long-long")
+set(CMAKE_CXX_FLAGS "-DUSE_STD_NAMESPACE -std=gnu++11 -pedantic -Wall -Wextra -Wno-long-long")
 
 set(CMAKE_CXX_FLAGS_RELEASE "-O3 -mtune=native -march=native -DNDEBUG -fomit-frame-pointer -ffast-math") # TODO -Ofast GCC 4.6
 set(CMAKE_C_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})

CMakeModules/FindTesseract.cmake

@@ -50,10 +50,8 @@ check_cxx_source_compiles(
    int main() {
    }"
   TESSERACT_NAMESPACE)
-if(TESSERACT_NAMESPACE)
-  add_definitions("-DCONFIG_TESSERACT_NAMESPACE")
-else()
-  message(WARNING "You are using an old Tesseract version. Support for Tesseract 2 is deprecated and will be removed in the future!")
+if(NOT TESSERACT_NAMESPACE)
+  message(FATAL_ERROR "You are using an old Tesseract version. Support for Tesseract 2 has been removed when implementing multithreading.")
 endif()
 list(REMOVE_ITEM CMAKE_REQUIRED_INCLUDES ${Tesseract_INCLUDE_DIR})
 

doc/completion.sh

@@ -44,7 +44,7 @@ _vobsub2srt() {
 
     case $cur in
         -*)
-            COMPREPLY=( $( compgen -W '--dump-images --verbose --ifo --lang --langlist --tesseract-lang --tesseract-data --blacklist --y-threshold --min-width --min-height' -- "$cur" ) )
+            COMPREPLY=( $( compgen -W '--dump-images --verbose --ifo --lang --langlist --tesseract-lang --tesseract-data --blacklist --y-threshold --min-width --min-height --max-threads' -- "$cur" ) )
             ;;
         *)
             _filedir '(idx|IDX|sub|SUB)'

doc/vobsub2srt.1

@@ -46,6 +46,9 @@ Minimum width in pixels to consider a subpicture for OCR (Default: 9).
 .TP
 \fB\-\-min-height\fR \fIheight\fR
 Minimum height in pixels to consider a subpicture for OCR (Default: 1).
+.TP
+\fB\-\-max\-threads\fR \fInb\fR
+Maximum number of threads to use to do the OCR, use 0 to autodetect the number of cores (Default: 0).
 .SH EXAMPLES
 .nf
   $ \fBvobsub2srt \-\-lang en foobar\fR

src/vobsub2srt.c++

@@ -26,10 +26,15 @@
 // Tesseract OCR
 #include "tesseract/baseapi.h"
 
+#include <unistd.h>
 #include <iostream>
 #include <string>
 #include <cstdio>
 #include <vector>
+#include <atomic>
+#include <algorithm>
+#include <thread>
+#include <mutex>
 using namespace std;
 
 #include "langcodes.h++"
@@ -40,10 +45,10 @@ typedef void* spu_t;
 
 // helper struct for caching and fixing end_pts in some cases
 struct sub_text_t {
-  sub_text_t(unsigned start_pts, unsigned end_pts, char const *text)
-    : start_pts(start_pts), end_pts(end_pts), text(text)
+  sub_text_t(unsigned counter, unsigned start_pts, unsigned end_pts, char const *text)
+    : counter(counter), start_pts(start_pts), end_pts(end_pts), text(text)
   { }
-  unsigned start_pts, end_pts;
+  unsigned counter, start_pts, end_pts;
   char const *text;
 };
 
@@ -83,15 +88,69 @@ void dump_pgm(std::string const &filename, unsigned counter, unsigned width, uns
   }
 }
 
-#ifdef CONFIG_TESSERACT_NAMESPACE
 using namespace tesseract;
-#endif
 
 #define TESSERACT_DEFAULT_PATH "<builtin default>"
 #ifndef TESSERACT_DATA_PATH
 #define TESSERACT_DATA_PATH TESSERACT_DEFAULT_PATH
 #endif
 
+TessBaseAPI* init_tesseract(std::string tesseract_data_path, char const *tess_lang, std::string blacklist) {
+  char const *tess_path = NULL;
+  if (tesseract_data_path != TESSERACT_DEFAULT_PATH)
+    tess_path = tesseract_data_path.c_str();
+
+  TessBaseAPI *tess_base_api = new TessBaseAPI();
+  if(tess_base_api->Init(tess_path, tess_lang) == -1) {
+    delete tess_base_api;
+    cerr << "Failed to initialize tesseract (OCR).\n";
+    return NULL;
+  }
+  if(not blacklist.empty()) {
+    tess_base_api->SetVariable("tessedit_char_blacklist", blacklist.c_str());
+  }
+  return tess_base_api;
+}
+
+void do_ocr(TessBaseAPI *tess_base_api, atomic<bool> *done, vector<sub_text_t> *conv_subs, mutex *mut,
+            unsigned counter, unsigned width, unsigned height, unsigned stride,
+            unsigned char *image_cpy, unsigned start_pts, unsigned end_pts, bool verb) {
+
+  char *text = tess_base_api->TesseractRect(image_cpy, 1, stride, 0, 0, width, height);
+  free(image_cpy);
+
+  if(not text) {
+    cerr << "ERROR: OCR failed for " << counter << '\n';
+    char const errormsg[] = "VobSub2SRT ERROR: OCR failure!";
+    // using raw memory is evil but that's the way Tesseract works
+    // If we switch to C++11 we can use unique_ptr.
+    text = new char[sizeof(errormsg)];
+    memcpy(text, errormsg, sizeof(errormsg));
+  }
+  else {
+    size_t size = strlen(text);
+    while (size > 0 and isspace(text[--size])) {
+      text[size] = '\0';
+    }
+  }
+  if(verb) {
+    cout << counter << " Text: " << text << endl;
+  }
+  mut->lock();
+  conv_subs->push_back(sub_text_t(counter, start_pts, end_pts, text));
+  mut->unlock();
+  done->store(true);
+}
+
+struct ocr_thread_t {
+  ocr_thread_t(TessBaseAPI *tess_base_api)
+    : tess_base_api(tess_base_api)
+  { }
+  thread *t = NULL;
+  atomic<bool> done{false};
+  TessBaseAPI *tess_base_api = NULL;
+};
+
 int main(int argc, char **argv) {
   bool dump_images = false;
   bool verb = false;
@@ -106,6 +165,7 @@ int main(int argc, char **argv) {
   int y_threshold = 0;
   int min_width = 9;
   int min_height = 1;
+  int max_threads = 0;
 
   {
     /************************************************************************************
@@ -125,6 +185,7 @@ int main(int argc, char **argv) {
       add_option("y-threshold", y_threshold, "Y (luminance) threshold below which colors treated as black (Default: 0)").
       add_option("min-width", min_width, "Minimum width in pixels to consider a subpicture for OCR (Default: 9)").
       add_option("min-height", min_height, "Minimum height in pixels to consider a subpicture for OCR (Default: 1)").
+      add_option("max-threads", max_threads, "Maximum number of threads to use to do the OCR, use 0 to autodetect the number of cores (Default: 0)").
       add_unnamed(subname, "subname", "name of the subtitle files WITHOUT .idx/.sub ending! (REQUIRED)");
     if(not opts.parse_cmd(argc, argv) or subname.empty()) {
       return 1;
@@ -200,27 +261,6 @@ int main(int argc, char **argv) {
     }
   }
 
-  // Init Tesseract
-  char const *tess_path = NULL;
-  if (tesseract_data_path != TESSERACT_DEFAULT_PATH)
-    tess_path = tesseract_data_path.c_str();
-
-#ifdef CONFIG_TESSERACT_NAMESPACE
-  TessBaseAPI tess_base_api;
-  if(tess_base_api.Init(tess_path, tess_lang) == -1) {
-    cerr << "Failed to initialize tesseract (OCR).\n";
-    return 1;
-  }
-  if(not blacklist.empty()) {
-    tess_base_api.SetVariable("tessedit_char_blacklist", blacklist.c_str());
-  }
-#else
-  TessBaseAPI::SimpleInit(tess_path, tess_lang, false); // TODO params
-  if(not blacklist.empty()) {
-    TessBaseAPI::SetVariable("tessedit_char_blacklist", blacklist.c_str());
-  }
-#endif
-
   // Open srt output file
   string const srt_filename = subname + ".srt";
   FILE *srtout = fopen(srt_filename.c_str(), "w");
@@ -229,14 +269,22 @@ int main(int argc, char **argv) {
     return 1;
   }
 
+  if (max_threads <= 0)
+    max_threads = thread::hardware_concurrency();
+
+  vector<ocr_thread_t*> threads;
+
   // Read subtitles and convert
   void *packet;
   int timestamp; // pts100
   int len;
   unsigned last_start_pts = 0;
   unsigned sub_counter = 1;
+
   vector<sub_text_t> conv_subs;
   conv_subs.reserve(200); // TODO better estimate
+  mutex mut;
+
   while( (len = vobsub_get_next_packet(vob, &packet, &timestamp)) > 0) {
     if(timestamp >= 0) {
       spudec_assemble(spu, reinterpret_cast<unsigned char*>(packet), len, timestamp);
@@ -269,50 +317,73 @@ int main(int argc, char **argv) {
         dump_pgm(subname, sub_counter, width, height, stride, image, image_size);
       }
 
-#ifdef CONFIG_TESSERACT_NAMESPACE
-      char *text = tess_base_api.TesseractRect(image, 1, stride, 0, 0, width, height);
-#else
-      char *text = TessBaseAPI::TesseractRect(image, 1, stride, 0, 0, width, height);
-#endif
-      if(not text) {
-        cerr << "ERROR: OCR failed for " << sub_counter << '\n';
-        char const errormsg[] = "VobSub2SRT ERROR: OCR failure!";
-        // using raw memory is evil but that's the way Tesseract works
-        // If we switch to C++11 we can use unique_ptr.
-        text = new char[sizeof(errormsg)];
-        memcpy(text, errormsg, sizeof(errormsg));
-      }
-      else {
-          size_t size = strlen(text);
-          while (size > 0 and isspace(text[--size])) {
-              text[size] = '\0';
+      ocr_thread_t *ocr_thread = NULL;
+      if (threads.size() < static_cast<unsigned>(max_threads)) {
+        TessBaseAPI *tess_base_api = init_tesseract(tesseract_data_path, tess_lang, blacklist);
+        if (tess_base_api == NULL)
+          return -1;
+        ocr_thread = new ocr_thread_t(tess_base_api);
+        threads.push_back(ocr_thread);
+      } else if (max_threads == 1) {
+        ocr_thread = threads[0];
+      } else {
+        while (ocr_thread == NULL) {
+          for (unsigned i=0; i < threads.size(); i++) {
+            if (threads[i]->done) {
+              threads[i]->t->join();
+              delete threads[i]->t;
+              ocr_thread = threads[i];
+              break;
+            }
           }
+          if (ocr_thread == NULL)
+            usleep(50);
+        }
       }
-      if(verb) {
-        cout << sub_counter << " Text: " << text << endl;
+
+      unsigned char *image_cpy = (unsigned char *)malloc(image_size);
+      memcpy(image_cpy, image, image_size);
+
+      if (max_threads == 1)
+        do_ocr(ocr_thread->tess_base_api, &ocr_thread->done, &conv_subs, &mut, sub_counter, width, height, stride, image_cpy, start_pts, end_pts, verb);
+      else {
+        ocr_thread->done = false;
+        ocr_thread->t = new thread(do_ocr, ocr_thread->tess_base_api, &ocr_thread->done, &conv_subs, &mut, sub_counter, width, height, stride, image_cpy, start_pts, end_pts, verb);
       }
-      conv_subs.push_back(sub_text_t(start_pts, end_pts, text));
+
       ++sub_counter;
     }
   }
 
+  for(unsigned i = 0; i < threads.size(); ++i) {
+    if (threads[i]->t != NULL) {
+      threads[i]->t->join();
+      delete threads[i]->t;
+    }
+    threads[i]->tess_base_api->End();
+    delete threads[i]->tess_base_api;
+    delete threads[i];
+  }
+
+  struct {
+      bool operator()(sub_text_t a, sub_text_t b) const {
+          return a.counter < b.counter;
+      }
+  } sort_fct;
+  sort(conv_subs.begin(), conv_subs.end(), sort_fct);
+
   // write the file, fixing end_pts when needed
   for(unsigned i = 0; i < conv_subs.size(); ++i) {
     if(conv_subs[i].end_pts == UINT_MAX && i+1 < conv_subs.size())
       conv_subs[i].end_pts = conv_subs[i+1].start_pts;
 
-    fprintf(srtout, "%u\n%s --> %s\n%s\n\n", i+1, pts2srt(conv_subs[i].start_pts).c_str(),
+    fprintf(srtout, "%u\n%s --> %s\n%s\n\n", conv_subs[i].counter, pts2srt(conv_subs[i].start_pts).c_str(),
             pts2srt(conv_subs[i].end_pts).c_str(), conv_subs[i].text);
 
     delete[]conv_subs[i].text;
     conv_subs[i].text = 0x0;
   }
 
-#ifdef CONFIG_TESSERACT_NAMESPACE
-  tess_base_api.End();
-#else
-  TessBaseAPI::End();
-#endif
   fclose(srtout);
   cout << "Wrote Subtitles to '" << srt_filename << "'\n";
   vobsub_close(vob);