From 89f35981615c1b8147d642119e69b44cd98638a9 Mon Sep 17 00:00:00 2001
From: Tuomas Virtanen <katajakasa@gmail.com>
Date: Tue, 2 Aug 2022 20:19:35 +0300
Subject: [PATCH] Add option for letting ffmpeg decide thread count

---
 examples/example_complex.c   |  4 ++--
 include/kitchensink/kitlib.h |  4 ++--
 src/internal/kitdecoder.c    | 12 +++++++++---
 src/kitlib.c                 |  2 +-
 4 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/examples/example_complex.c b/examples/example_complex.c
index 8af8c3a..3a57695 100644
--- a/examples/example_complex.c
+++ b/examples/example_complex.c
@@ -108,8 +108,8 @@ int main(int argc, char *argv[]) {
         return 1;
     }
 
-    // Allow Kit to use more threads
-    Kit_SetHint(KIT_HINT_THREAD_COUNT, SDL_GetCPUCount() <= 4 ? SDL_GetCPUCount() : 4);
+    // Set to 0 to allow ffmpeg decide thread count.
+    Kit_SetHint(KIT_HINT_THREAD_COUNT, 0);
 
     // Lots of buffers for smooth playback (will eat up more memory, too).
     Kit_SetHint(KIT_HINT_VIDEO_BUFFER_FRAMES, 5);
diff --git a/include/kitchensink/kitlib.h b/include/kitchensink/kitlib.h
index a5fe913..f562c5a 100644
--- a/include/kitchensink/kitlib.h
+++ b/include/kitchensink/kitlib.h
@@ -42,7 +42,7 @@ typedef struct Kit_Version {
  */
 typedef enum Kit_HintType {
     KIT_HINT_FONT_HINTING, ///< Set font hinting mode (currently used for libass)
-    KIT_HINT_THREAD_COUNT, ///< Set thread count for ffmpeg (1 by default)
+    KIT_HINT_THREAD_COUNT, ///< Set thread count for ffmpeg (1 by default). Set to 0 for autodetect.
     KIT_HINT_VIDEO_BUFFER_FRAMES, ///< Video output buffer frames (3 by default)
     KIT_HINT_AUDIO_BUFFER_FRAMES, ///< Audio output buffers (64 by default)
     KIT_HINT_SUBTITLE_BUFFER_FRAMES ///< Subtitle output buffers (64 by default, used by image subtitles)
@@ -90,7 +90,7 @@ KIT_API int Kit_Init(unsigned int flags);
 KIT_API void Kit_Quit();
 
 /**
- * @brief Sets a librarywide hint
+ * @brief Sets a library-wide hint
  * 
  * This can be used to set hints on how the library should behave. See Kit_HintType
  * for all the options.
diff --git a/src/internal/kitdecoder.c b/src/internal/kitdecoder.c
index e8093b6..c20bd86 100644
--- a/src/internal/kitdecoder.c
+++ b/src/internal/kitdecoder.c
@@ -17,7 +17,7 @@ Kit_Decoder* Kit_CreateDecoder(const Kit_Source *src, int stream_index,
                                int thread_count) {
     assert(src != NULL);
     assert(out_b_size > 0);
-    assert(thread_count > 0);
+    assert(thread_count >= 0);
 
     AVCodecContext *codec_ctx = NULL;
     AVDictionary *codec_opts = NULL;
@@ -61,9 +61,15 @@ Kit_Decoder* Kit_CreateDecoder(const Kit_Source *src, int stream_index,
 
     codec_ctx->pkt_timebase = format_ctx->streams[stream_index]->time_base;
 
-    // Set thread count
+    // Set threading, if possible
     codec_ctx->thread_count = thread_count;
-    codec_ctx->thread_type = FF_THREAD_SLICE|FF_THREAD_FRAME;
+    if(codec->capabilities | AV_CODEC_CAP_FRAME_THREADS) {
+        codec_ctx->thread_type = FF_THREAD_FRAME;
+    } else if(codec->capabilities | AV_CODEC_CAP_SLICE_THREADS) {
+        codec_ctx->thread_type = FF_THREAD_SLICE;
+    } else {
+        codec_ctx->thread_count = 1;  // Disable threading
+    }
 
     // This is required for ass_process_chunk()
     av_dict_set(&codec_opts, "sub_text_format", "ass", 0);
diff --git a/src/kitlib.c b/src/kitlib.c
index fd4c2bd..4fa1298 100644
--- a/src/kitlib.c
+++ b/src/kitlib.c
@@ -89,7 +89,7 @@ void Kit_SetHint(Kit_HintType type, int value) {
     Kit_LibraryState *state = Kit_GetLibraryState();
     switch(type) {
         case KIT_HINT_THREAD_COUNT:
-            state->thread_count =  max(value, 1);
+            state->thread_count =  max(value, 0);
             break;
         case KIT_HINT_FONT_HINTING:
             state->font_hinting = max(min(value, KIT_FONT_HINTING_COUNT), 0);