Make video providers report whether their file has audio tracks

Fixes errors when trying to automatically open audio from dummy video
and improves UX a little by disabling the Open Audio From Video menu
item when there are no audio tracks.

src/async_video_provider.h

@@ -111,6 +111,7 @@ public:
 	std::string GetWarning() const        { return source_provider->GetWarning(); }
 	std::string GetDecoderName() const    { return source_provider->GetDecoderName(); }
 	bool ShouldSetVideoProperties() const { return source_provider->ShouldSetVideoProperties(); }
+	bool HasAudio() const                 { return source_provider->HasAudio(); }
 
 	/// @brief Constructor
 	/// @param videoFileName File to open

src/command/audio.cpp

@@ -32,6 +32,7 @@
 #include "command.h"
 
 #include "../ass_dialogue.h"
+#include "../async_video_provider.h"
 #include "../audio_box.h"
 #include "../audio_controller.h"
 #include "../audio_karaoke.h"
@@ -118,7 +119,7 @@ struct audio_open_video final : public Command {
 	CMD_TYPE(COMMAND_VALIDATE)
 
 	bool Validate(const agi::Context *c) override {
-		return !c->project->VideoName().empty();
+		return c->project->VideoProvider() && c->project->VideoProvider()->HasAudio();
 	}
 
 	void operator()(agi::Context *c) override {

src/include/aegisub/video_provider.h

@@ -81,6 +81,9 @@ public:
 
 	/// Should the video properties in the script be set to this video's property if they already have values?
 	virtual bool ShouldSetVideoProperties() const { return true; }
+
+	/// Does the file which this provider is reading have an audio track?
+	virtual bool HasAudio() const { return false; }
 };
 
 DEFINE_BASE_EXCEPTION_NOINNER(VideoProviderError, agi::Exception)

src/project.cpp

@@ -295,8 +295,9 @@ bool Project::DoLoadVideo(agi::fs::path const& path) {
 }
 
 void Project::LoadVideo(agi::fs::path const& path) {
+	if (path.empty()) return;
 	if (!DoLoadVideo(path)) return;
-	if (OPT_GET("Video/Open Audio")->GetBool() && audio_file != video_file)
+	if (OPT_GET("Video/Open Audio")->GetBool() && audio_file != video_file && video_provider->HasAudio())
 		DoLoadAudio(video_file, true);
 }
 

src/video_provider_avs.cpp

@@ -27,11 +27,6 @@
 //
 // Aegisub Project http://www.aegisub.org/
 
-/// @file video_provider_avs.cpp
-/// @brief Avisynth-based video provider
-/// @ingroup video_input
-///
-
 #ifdef WITH_AVISYNTH
 #include "include/aegisub/video_provider.h"
 
@@ -66,6 +61,7 @@ class AvisynthVideoProvider: public VideoProvider {
 	std::string warning;
 	std::string colorspace;
 	std::string real_colorspace;
+	bool has_audio = false;
 
 	AVSValue source_clip;
 	PClip RGB32Video;
@@ -94,6 +90,7 @@ public:
 	std::string GetDecoderName() const override    { return decoder_name; }
 	std::string GetColorSpace() const override     { return colorspace; }
 	std::string GetRealColorSpace() const override { return real_colorspace; }
+	bool HasAudio() const override                 { return has_audio; }
 };
 
 AvisynthVideoProvider::AvisynthVideoProvider(agi::fs::path const& filename, std::string const& colormatrix) {
@@ -189,6 +186,7 @@ file_exit:
 void AvisynthVideoProvider::Init(std::string const& colormatrix) {
 	auto script = source_clip;
 	vi = script.AsClip()->GetVideoInfo();
+	has_audio = vi.HasAudio();
 	if (vi.IsRGB())
 		real_colorspace = colorspace = "None";
 	else {

src/video_provider_cache.cpp

@@ -74,6 +74,8 @@ public:
 	std::string GetDecoderName() const override    { return master->GetDecoderName(); }
 	std::string GetColorSpace() const override     { return master->GetColorSpace(); }
 	std::string GetRealColorSpace() const override { return master->GetRealColorSpace(); }
+	bool ShouldSetVideoProperties() const override { return master->ShouldSetVideoProperties(); }
+	bool HasAudio() const override                 { return master->HasAudio(); }
 };
 
 std::shared_ptr<VideoFrame> VideoProviderCache::GetFrame(int n) {

src/video_provider_ffmpegsource.cpp

@@ -63,6 +63,7 @@ class FFmpegSourceVideoProvider final : public VideoProvider, FFmpegSourceProvid
 
 	char FFMSErrMsg[1024];          ///< FFMS error message
 	FFMS_ErrorInfo ErrInfo;         ///< FFMS error codes/messages
+	bool has_audio = false;
 
 	void LoadVideo(agi::fs::path const& filename, std::string const& colormatrix);
 
@@ -94,6 +95,7 @@ public:
 	std::vector<int> GetKeyFrames() const override { return KeyFramesList; };
 	std::string GetDecoderName() const override    { return "FFmpegSource"; }
 	bool WantsCaching() const override             { return true; }
+	bool HasAudio() const override                 { return has_audio; }
 };
 
 std::string colormatrix_description(int cs, int cr) {
@@ -204,6 +206,9 @@ void FFmpegSourceVideoProvider::LoadVideo(agi::fs::path const& filename, std::st
 			throw VideoNotSupported(std::string("Couldn't find any video tracks: ") + ErrInfo.Buffer);
 	}
 
+	// Check if there's an audio track
+	has_audio = FFMS_GetFirstTrackOfType(Index, FFMS_TYPE_AUDIO, nullptr) != -1;
+
 	// set thread count
 	int Threads = OPT_GET("Provider/Video/FFmpegSource/Decoding Threads")->GetInt();
 	if (FFMS_GetVersion() < ((2 << 24) | (17 << 16) | (2 << 8) | 1) && FFMS_GetSourceType(Index) == FFMS_SOURCE_LAVF)