avcodec/mfenc: Dynamically load MFPlat.DLL

Allows non-UWP builds of FFmpeg with MediaFoundation to work on
N editions of Windows which are without MediaFoundation by default.

On UWP target, FFmpeg is linked directly against MediaFoundation since
LoadLibrary is not available.

This commit adresses https://trac.ffmpeg.org/ticket/9788

Signed-off-by: Martin Storsjö <martin@martin.st>

1 files changed, 84 insertions, 9 deletions

diff --git a/libavcodec/mfenc.c b/libavcodec/mfenc.c
index 280941cf2e..17d0ec60bd 100644
--- a/libavcodec/mfenc.c
+++ b/libavcodec/mfenc.c
@@ -32,6 +32,8 @@
 
 typedef struct MFContext {
     AVClass *av_class;
+    HMODULE library;
+    MFFunctions functions;
     AVFrame *frame;
     int is_video, is_audio;
     GUID main_subtype;
@@ -292,7 +294,8 @@ static IMFSample *mf_a_avframe_to_sample(AVCodecContext *avctx, const AVFrame *f
     bps = av_get_bytes_per_sample(avctx->sample_fmt) * avctx->ch_layout.nb_channels;
     len = frame->nb_samples * bps;
 
-    sample = ff_create_memory_sample(frame->data[0], len, c->in_info.cbAlignment);
+    sample = ff_create_memory_sample(&c->functions, frame->data[0], len,
+                                     c->in_info.cbAlignment);
     if (sample)
         IMFSample_SetSampleDuration(sample, mf_to_mf_time(avctx, frame->nb_samples));
     return sample;
@@ -312,7 +315,8 @@ static IMFSample *mf_v_avframe_to_sample(AVCodecContext *avctx, const AVFrame *f
     if (size < 0)
         return NULL;
 
-    sample = ff_create_memory_sample(NULL, size, c->in_info.cbAlignment);
+    sample = ff_create_memory_sample(&c->functions, NULL, size,
+                                     c->in_info.cbAlignment);
     if (!sample)
         return NULL;
 
@@ -422,7 +426,9 @@ static int mf_receive_sample(AVCodecContext *avctx, IMFSample **out_sample)
         }
 
         if (!c->out_stream_provides_samples) {
-            sample = ff_create_memory_sample(NULL, c->out_info.cbSize, c->out_info.cbAlignment);
+            sample = ff_create_memory_sample(&c->functions, NULL,
+                                             c->out_info.cbSize,
+                                             c->out_info.cbAlignment);
             if (!sample)
                 return AVERROR(ENOMEM);
         }
@@ -777,7 +783,7 @@ static int mf_choose_output_type(AVCodecContext *avctx)
     if (out_type) {
         av_log(avctx, AV_LOG_VERBOSE, "picking output type %d.\n", out_type_index);
     } else {
-        hr = MFCreateMediaType(&out_type);
+        hr = c->functions.MFCreateMediaType(&out_type);
         if (FAILED(hr)) {
             ret = AVERROR(ENOMEM);
             goto done;
@@ -1005,7 +1011,8 @@ err:
     return res;
 }
 
-static int mf_create(void *log, IMFTransform **mft, const AVCodec *codec, int use_hw)
+static int mf_create(void *log, MFFunctions *f, IMFTransform **mft,
+                     const AVCodec *codec, int use_hw)
 {
     int is_audio = codec->type == AVMEDIA_TYPE_AUDIO;
     const CLSID *subtype = ff_codec_to_mf_subtype(codec->id);
@@ -1028,13 +1035,13 @@ static int mf_create(void *log, IMFTransform **mft, const AVCodec *codec, int us
         category = MFT_CATEGORY_VIDEO_ENCODER;
     }
 
-    if ((ret = ff_instantiate_mf(log, category, NULL, &reg, use_hw, mft)) < 0)
+    if ((ret = ff_instantiate_mf(log, f, category, NULL, &reg, use_hw, mft)) < 0)
         return ret;
 
     return 0;
 }
 
-static int mf_init(AVCodecContext *avctx)
+static int mf_init_encoder(AVCodecContext *avctx)
 {
     MFContext *c = avctx->priv_data;
     HRESULT hr;
@@ -1058,7 +1065,7 @@ static int mf_init(AVCodecContext *avctx)
 
     c->main_subtype = *subtype;
 
-    if ((ret = mf_create(avctx, &c->mft, avctx->codec, use_hw)) < 0)
+    if ((ret = mf_create(avctx, &c->functions, &c->mft, avctx->codec, use_hw)) < 0)
         return ret;
 
     if ((ret = mf_unlock_async(avctx)) < 0)
@@ -1122,6 +1129,54 @@ static int mf_init(AVCodecContext *avctx)
     return 0;
 }
 
+#if !HAVE_UWP
+#define LOAD_MF_FUNCTION(context, func_name) \
+    context->functions.func_name = (void *)GetProcAddress(context->library, #func_name); \
+    if (!context->functions.func_name) { \
+        av_log(context, AV_LOG_ERROR, "DLL mfplat.dll failed to find function "\
+           #func_name "\n"); \
+        return AVERROR_UNKNOWN; \
+    }
+#else
+// In UWP (which lacks LoadLibrary), just link directly against
+// the functions - this requires building with new/complete enough
+// import libraries.
+#define LOAD_MF_FUNCTION(context, func_name) \
+    context->functions.func_name = func_name; \
+    if (!context->functions.func_name) { \
+        av_log(context, AV_LOG_ERROR, "Failed to find function " #func_name \
+               "\n"); \
+        return AVERROR_UNKNOWN; \
+    }
+#endif
+
+// Windows N editions does not provide MediaFoundation by default.
+// So to avoid DLL loading error, MediaFoundation is dynamically loaded except
+// on UWP build since LoadLibrary is not available on it.
+static int mf_load_library(AVCodecContext *avctx)
+{
+    MFContext *c = avctx->priv_data;
+
+#if !HAVE_UWP
+    c->library = LoadLibraryA("mfplat.dll");
+
+    if (!c->library) {
+        av_log(c, AV_LOG_ERROR, "DLL mfplat.dll failed to open\n");
+        return AVERROR_UNKNOWN;
+    }
+#endif
+
+    LOAD_MF_FUNCTION(c, MFStartup);
+    LOAD_MF_FUNCTION(c, MFShutdown);
+    LOAD_MF_FUNCTION(c, MFCreateAlignedMemoryBuffer);
+    LOAD_MF_FUNCTION(c, MFCreateSample);
+    LOAD_MF_FUNCTION(c, MFCreateMediaType);
+    // MFTEnumEx is missing in Windows Vista's mfplat.dll.
+    LOAD_MF_FUNCTION(c, MFTEnumEx);
+
+    return 0;
+}
+
 static int mf_close(AVCodecContext *avctx)
 {
     MFContext *c = avctx->priv_data;
@@ -1132,7 +1187,15 @@ static int mf_close(AVCodecContext *avctx)
     if (c->async_events)
         IMFMediaEventGenerator_Release(c->async_events);
 
-    ff_free_mf(&c->mft);
+#if !HAVE_UWP
+    if (c->library)
+        ff_free_mf(&c->functions, &c->mft);
+
+    FreeLibrary(c->library);
+    c->library = NULL;
+#else
+    ff_free_mf(&c->functions, &c->mft);
+#endif
 
     av_frame_free(&c->frame);
 
@@ -1142,6 +1205,18 @@ static int mf_close(AVCodecContext *avctx)
     return 0;
 }
 
+static int mf_init(AVCodecContext *avctx)
+{
+    int ret;
+    if ((ret = mf_load_library(avctx)) == 0) {
+           if ((ret = mf_init_encoder(avctx)) == 0) {
+                return 0;
+        }
+    }
+    mf_close(avctx);
+    return ret;
+}
+
 #define OFFSET(x) offsetof(MFContext, x)
 
 #define MF_ENCODER(MEDIATYPE, NAME, ID, OPTS, EXTRA) \