[FFmpeg] added save_frame() and improved picking of codecs when not specified (#2800)

* WIP

* - pick best codec
- added save_frame()
- fixed example

* Add missing variable declaration

* added extensions
fixed tests

* attempt to set quality as high as possible. lower expected PSNR

* arrufat suggestion

* refactoring

---------

Co-authored-by: Your name <you@example.com>
Co-authored-by: pf <pf@me>
Co-authored-by: Adrià Arrufat <1671644+arrufat@users.noreply.github.com>

dlib/media/ffmpeg_demuxer.h

@@ -1627,7 +1627,7 @@ namespace dlib
         inline void load_frame(image_type& image, const std::string& file_name)
         {
             if (!demuxer({file_name, video_enabled, audio_disabled}).read(image))
-                throw error("ffmpeg::load_frame: error while loading " + file_name);
+                throw error(EIMAGE_LOAD, "ffmpeg::load_frame: error while loading " + file_name);
         }
 
 // ---------------------------------------------------------------------------------------------------

dlib/media/ffmpeg_details.h

@@ -480,6 +480,47 @@ namespace dlib { namespace ffmpeg { namespace details
         }
     }    
 
+// ---------------------------------------------------------------------------------------------------
+
+    inline AVCodecID pick_codec_from_filename(const std::string& filename)
+    {
+        const auto ext_pos = filename.find_last_of(".");
+
+        if (ext_pos != std::string::npos)
+        {
+            const std::string ext = filename.substr(ext_pos + 1);
+
+            if (ext == "png" || ext == "PNG")
+                return AV_CODEC_ID_PNG;
+            else if (ext == "jpeg" || ext == "jpg" || ext == "JPEG")
+                return AV_CODEC_ID_MJPEG;
+            else if (ext == "tiff")
+                return AV_CODEC_ID_TIFF;
+            else if (ext == "webp")
+                return AV_CODEC_ID_WEBP;
+            else if (ext == "bmp")
+                return AV_CODEC_ID_BMP;
+            else if (ext == "h264")
+                return AV_CODEC_ID_H264;
+            else if (ext == "h265" || ext == "hevc")
+                return AV_CODEC_ID_H265;
+            else if (ext == "aac")
+                return AV_CODEC_ID_AAC;
+            else if (ext == "ac3")
+                return AV_CODEC_ID_AC3;
+            else if (ext == "jls")
+                return AV_CODEC_ID_JPEGLS;
+            else if (ext == "jp2")
+                return AV_CODEC_ID_JPEG2000;
+#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(59, 37, 100)
+            else if (ext == "jxl")
+                return AV_CODEC_ID_JPEGXL;
+#endif
+        }
+
+        return AV_CODEC_ID_NONE;
+    }
+
 // ---------------------------------------------------------------------------------------------------
 
 }}}

dlib/media/ffmpeg_muxer.h

@@ -634,6 +634,24 @@ namespace dlib
             } st;
         };
 
+// ---------------------------------------------------------------------------------------------------
+
+        template <
+          class image_type,
+          is_image_check<image_type> = true
+        >
+        void save_frame(
+            const image_type& image,
+            const std::string& file_name,
+            const std::unordered_map<std::string, std::string>& codec_options = {}
+        );
+        /*!
+            requires
+                - image_type must be a type conforming to the generic image interface.
+            ensures
+                - encodes the image into the file pointed by file_name using options described in codec_options.
+        !*/
+
 // ---------------------------------------------------------------------------------------------------
 
     }
@@ -822,10 +840,64 @@ namespace dlib
                 }
 #endif
             }
+
+// ---------------------------------------------------------------------------------------------------
+
+            inline bool check_codecs (
+                const bool              is_video,
+                const std::string&      filename,
+                const AVOutputFormat*   oformat,
+                encoder::args&          args
+            )
+            {
+                // Check the codec is supported by this muxer
+                const auto supported_codecs = list_codecs_for_muxer(oformat);
+
+                const auto codec_supported = [&](AVCodecID id, const std::string& name)
+                {
+                    return std::find_if(begin(supported_codecs), end(supported_codecs), [&](const auto& supported) {
+                        return id != AV_CODEC_ID_NONE ? id == supported.codec_id : name == supported.codec_name;
+                    }) != end(supported_codecs);
+                };
+
+                if (codec_supported(args.args_codec.codec, args.args_codec.codec_name))
+                    return true;
+
+                logger_dlib_wrapper() << LWARN
+                    << "Codec " << avcodec_get_name(args.args_codec.codec) << " or " << args.args_codec.codec_name
+                    << " cannot be stored in this file";
+
+                // Pick codec based on file extension
+                args.args_codec.codec = pick_codec_from_filename(filename);
+
+                if (codec_supported(args.args_codec.codec, ""))
+                {
+                    logger_dlib_wrapper() << LWARN  << "Picking codec " << avcodec_get_name(args.args_codec.codec);
+                    return true;
+                }
+                    
+                // Pick the default codec as suggested by FFmpeg
+                args.args_codec.codec = is_video ? oformat->video_codec : oformat->audio_codec;
+
+                if (args.args_codec.codec != AV_CODEC_ID_NONE)
+                {
+                    logger_dlib_wrapper() << LWARN  << "Picking default codec " << avcodec_get_name(args.args_codec.codec);
+                    return true;
+                }
+                    
+                logger_dlib_wrapper() << LWARN 
+                    << "List of supported codecs for muxer " << oformat->name << " in this installation of ffmpeg:";
+
+                for (const auto& supported : supported_codecs)
+                    logger_dlib_wrapper() << LWARN << "    " << supported.codec_name;
+                        
+                return false;
             }
 
 // ---------------------------------------------------------------------------------------------------
 
+        }
+
         inline encoder::encoder(
             const args& a
         ) : args_(a)
@@ -1188,37 +1260,8 @@ namespace dlib
                 if (st.pFormatCtx->oformat->flags & AVFMT_GLOBALHEADER)
                     args.args_codec.flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
 
-                // Before we create the encoder, check the codec is supported by this muxer
+                if (!check_codecs(is_video, st.args_.filepath, st.pFormatCtx->oformat, args))
-                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 ? 
-                                supported.codec_id   == args.args_codec.codec :
-                                supported.codec_name == args.args_codec.codec_name;
-                }) == end(supported_codecs))
-                {
-                    logger_dlib_wrapper() << LWARN
-                        << "Codec " << avcodec_get_name(args.args_codec.codec) << " or " << args.args_codec.codec_name
-                        << " cannot be stored in this file";
-                    
-                    args.args_codec.codec = is_video ? st.pFormatCtx->oformat->video_codec : 
-                                                       st.pFormatCtx->oformat->audio_codec;
-                    
-                    if (args.args_codec.codec != AV_CODEC_ID_NONE)
-                    {
-                        logger_dlib_wrapper() << LWARN 
-                            << "Picking default codec " << avcodec_get_name(args.args_codec.codec);
-                    }
-                    else
-                    {
-                        logger_dlib_wrapper() << LWARN 
-                            << "List of supported codecs for muxer " << st.pFormatCtx->oformat->name << " in this installation of ffmpeg:";
-                        for (const auto& supported : supported_codecs)
-                            logger_dlib_wrapper() << LWARN << "    " << supported.codec_name;
-                        
                     return false;
-                    }    
-                }
 
                 // Codec is supported by muxer, so create encoder
                 enc = encoder(args);
@@ -1381,6 +1424,36 @@ namespace dlib
         inline AVCodecID        muxer::get_audio_codec_id()     const noexcept { return st.encoder_audio.get_codec_id(); }
         inline std::string      muxer::get_audio_codec_name()   const noexcept { return st.encoder_audio.get_codec_name(); }
 
+// ---------------------------------------------------------------------------------------------------
+
+        template <
+          class image_type,
+          is_image_check<image_type>
+        >
+        inline void save_frame(
+            const image_type& image,
+            const std::string& file_name,
+            const std::unordered_map<std::string, std::string>& codec_options
+        )
+        {
+            muxer writer([&] {
+                muxer::args args;
+                args.filepath               = file_name;
+                args.enable_image           = true;
+                args.enable_audio           = false;
+                args.args_image.h           = num_rows(image);
+                args.args_image.w           = num_columns(image);
+                args.args_image.framerate   = 1;
+                args.args_image.fmt         = pix_traits<pixel_type_t<image_type>>::fmt;
+                args.args_image.codec_options = codec_options;
+                args.format_options["update"] = "1";
+                return args;
+            }());
+
+            if (!writer.push(image))
+                throw error(EIMAGE_SAVE, "ffmpeg::save_frame: error while saving " + file_name);
+        }
+
 // ---------------------------------------------------------------------------------------------------
 
     }

dlib/test/ffmpeg.cpp

@@ -146,6 +146,21 @@ namespace
         DLIB_TEST_MSG(similarity > 25.0, "psnr " << similarity);
     }
 
+    template<class pixel_type>
+    void test_load_save_frame(const std::string& filename)
+    {
+        matrix<pixel_type> img1, img2;
+        img1 = get_random_image<pixel_type>();
+
+        save_frame(img1, filename, {{"qmin", "1"}, {"qmax", "1"}});
+        load_frame(img2, filename);
+
+        DLIB_TEST(img1.nr() == img2.nr());
+        DLIB_TEST(img1.nc() == img2.nc());
+        const double similarity = psnr(img1, img2);
+        DLIB_TEST_MSG(similarity > 20.0, "psnr " << similarity);
+    }
+
 //////////////////////////////////////////////////////////////////////////////////////////////////////
 //////////////////////////////////////////////////////////////////////////////////////////////////////
 // DECODER
@@ -784,6 +799,13 @@ namespace
         DLIB_TEST(samples <= (nsamples + rate));
     }
 
+    const auto codec_supported = [](const AVCodecID id)
+    {
+        return std::find_if(begin(list_codecs()), end(list_codecs()), [=](const auto& supported) {
+            return supported.codec_id == id && supported.supports_encoding;
+        }) != end(list_codecs());
+    };
+
     class video_tester : public tester
     {
     public:
@@ -802,6 +824,30 @@ namespace
                 test_frame<bgr_pixel>();
                 test_frame<rgb_alpha_pixel>();
                 test_frame<bgr_alpha_pixel>();
+
+                if (codec_supported(AV_CODEC_ID_PNG))
+                {
+                    test_load_save_frame<rgb_pixel>("dummy.png");
+                    test_load_save_frame<bgr_pixel>("dummy.png");
+                }
+
+                if (codec_supported(AV_CODEC_ID_MJPEG))
+                {
+                    test_load_save_frame<rgb_pixel>("dummy.jpg");
+                    test_load_save_frame<bgr_pixel>("dummy.jpg");
+                }
+
+                if (codec_supported(AV_CODEC_ID_BMP))
+                {
+                    test_load_save_frame<rgb_pixel>("dummy.bmp");
+                    test_load_save_frame<bgr_pixel>("dummy.bmp");
+                }
+
+                if (codec_supported(AV_CODEC_ID_TIFF))
+                {
+                    test_load_save_frame<rgb_pixel>("dummy.tiff");
+                    test_load_save_frame<bgr_pixel>("dummy.tiff");
+                }
             }
 
             dlib::file f(DLIB_FFMPEG_DATA);

examples/ffmpeg_file_to_speaker_ex.cpp

@@ -40,7 +40,7 @@ try
     
     const std::string filename  = get_option(parser, "i",       "");
     const std::string device    = get_option(parser, "o",       "hw:0,0");
-    const std::string codec     = get_option(parser, "codec",   "pcm_s16le");
+    const std::string codec     = get_option(parser, "codec",   "");
 
     if (device.empty())
     {
@@ -65,7 +65,7 @@ try
         args.enable_image               = false;
         args.args_audio.codec_name      = codec;
         args.args_audio.sample_rate     = 44100;
-        args.args_audio.channel_layout  = cap.channel_layout();
+        args.args_audio.channel_layout  = AV_CH_LAYOUT_STEREO;
         args.args_audio.fmt             = cap.sample_fmt();
         return args;
     }());