FFmpeg : improvements to ffmpeg::list() functions (davisking#2773)

* added a couple more audio examples * statically initialize all list_() functions where possible. --------- Co-authored-by: pf <pf@me>
PowerLay · Apr 15, 2023 · 5f7026a · 5f7026a
1 parent b1fe026
commit 5f7026a
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Showing 4 changed files with 269 additions and 188 deletions.
diff --git a/dlib/media/ffmpeg_abstract.h b/dlib/media/ffmpeg_abstract.h
@@ -296,55 +296,73 @@ namespace dlib
         {
             /*!
                 WHAT THIS OBJECT REPRESENTS
-                    This object informs on available devices provided by the installation of ffmpeg dlib is linked against.
+                    This object informs on available device types provided by the installation of ffmpeg dlib is linked against.
             !*/
 
-            struct instance
-            {
-                std::string name;
-                std::string description;
-            };
-
             std::string device_type;
-            std::vector<instance> devices;
+            bool        is_audio_type{false};
+            bool        is_video_type{false};
         };
 
-        std::vector<std::string> list_protocols();
+        struct device_instance
+        {
+            /*!
+                WHAT THIS OBJECT REPRESENTS
+                    This object informs on the currently available device instances readable by ffmpeg.
+            !*/
+
+            std::string name;
+            std::string description;
+        };
+
+        const std::vector<std::string>& list_protocols();
         /*!
             ensures
-                - returns a list of all registered ffmpeg protocols
+                - returns a list of all available ffmpeg protocols
         !*/
 
-        std::vector<std::string> list_demuxers();
+        const std::vector<std::string>& list_demuxers();
         /*!
             ensures
-                - returns a list of all registered ffmpeg demuxers
+                - returns a list of all available ffmpeg demuxers
         !*/
 
-        std::vector<muxer_details> list_muxers();
+        const std::vector<muxer_details>& list_muxers();
         /*!
             ensures
-                - returns a list of all registered ffmpeg muxers
+                - returns a list of all available ffmpeg muxers
         !*/
 
-        std::vector<codec_details> list_codecs();
+        const std::vector<codec_details>& list_codecs();
         /*!
             ensures
-                - returns a list of all registered ffmpeg codecs with information on whether decoding and/or encoding is supported.
+                - returns a list of all available ffmpeg codecs with information on whether decoding and/or encoding is supported.
                   Note that not all codecs support encoding, unless your installation of ffmpeg is built with third party library
                   dependencies like libx264, libx265, etc.
         !*/
 
-        std::vector<device_details> list_input_devices();
+        const std::vector<device_details>& list_input_device_types();
+        /*!
+            ensures
+                - returns a list of all available ffmpeg input device types (e.g. alsa, v4l2, etc)
+        !*/
+
+        const std::vector<device_details>& list_output_device_types();
+        /*!
+            ensures
+                - returns a list of all available ffmpeg output device types (e.g. alsa, v4l2, etc)
+        !*/
+
+        std::vector<device_instance> list_input_device_instances(const std::string& device_type);
         /*!
             ensures
-                - returns a list of all registered ffmpeg input devices and available instances of those devices
+                - returns a list of all available ffmpeg input device instances for device type *device_type (e.g. hw:0,0, /dev/video0, etc)
         !*/
 
-        std::vector<device_details> list_output_devices();
+        std::vector<device_instance> list_output_device_instances(const std::string& device_type);
         /*!
             ensures
-                - returns a list of all registered ffmpeg output devices and available instances of those devices
+                - returns a list of all available ffmpeg output device instances for device type *device_type (e.g. hw:0,0, /dev/video0, etc)
         !*/
 
 // ---------------------------------------------------------------------------------------------------

diff --git a/dlib/media/ffmpeg_muxer.h b/dlib/media/ffmpeg_muxer.h
@@ -662,8 +662,6 @@ namespace dlib
             if (!st.args_.enable_audio && !st.args_.enable_image)
                 return fail(*st.log, "You need to set at least one of `enable_audio` or `enable_image`");
 
-            static const auto all_codecs = list_codecs();
-
             {
                 st.connecting_time = system_clock::now();
                 st.connected_time  = system_clock::time_point::max();
@@ -723,7 +721,7 @@ namespace dlib
                 };
 
                 // Before we create the encoder, check the codec is supported by this muxer
-                const auto supported_codecs = list_codecs_for_muxer(st.pFormatCtx->oformat, all_codecs);
+                const auto supported_codecs = list_codecs_for_muxer(st.pFormatCtx->oformat);
 
                 if (std::find_if(begin(supported_codecs), end(supported_codecs), [&](const auto& supported) {
                     return args.args_codec.codec != AV_CODEC_ID_NONE ?