proxy: isolate proxies from export renders and improve proxy workflow

- FootageJob::should_use_proxy() centralizes the proxy decision; worker
  pre-decode now honors the render mode so exports always decode the
  original media (previously every frame was pre-decoded from proxies)
- global Tools > Use Proxy Media toggle with footage invalidation
- ffmpeg -progress parsing for real percentage feedback while generating
- divider mode (1/2, 1/4, 1/8 of source resolution) with UI, proxy
  filename tags and per-footage persistence (pdivider)
- Media Offline warning slat rendered for missing footage
- regression tests: export isolation, relink invalidation, offline slat,
  progress parsing, divider arguments

app/render/job/footagejob.h

@@ -22,7 +22,10 @@
 #ifndef OAK_FOOTAGEJOB_H
 #define OAK_FOOTAGEJOB_H
 
+#include <QFileInfo>
+
 #include "node/project/footage/footage.h"
+#include "render/rendermodes.h"
 
 namespace olive
 {
@@ -85,6 +88,20 @@ public:
 		has_proxy_ = !filename.isEmpty();
 	}
 
+	/**
+	 * @brief Whether decoding for the given render mode should use the proxy
+	 *
+	 * Proxies are a preview accelerator only: offline (realtime preview)
+	 * renders may decode from them, online (export/master) renders must
+	 * always decode the original media. The proxy file must also still
+	 * exist on disk, otherwise decoding falls back to the original.
+	 */
+	bool should_use_proxy(RenderMode::Mode mode) const
+	{
+		return mode == RenderMode::k_offline && has_proxy() &&
+			QFileInfo::exists(proxy_filename_);
+	}
+
 	Track::Type type() const
 	{
 		return type_;

app/render/renderprocessor.cpp

@@ -530,10 +530,8 @@ void RenderProcessor::process_video_footage(TexturePtr destination,
 		return;
 	}
 
-	const bool use_proxy =
-		static_cast<RenderMode::Mode>(ticket_->property("mode").toInt()) ==
-			RenderMode::k_offline &&
-		stream->has_proxy() && QFileInfo::exists(stream->proxy_filename());
+	const bool use_proxy = stream->should_use_proxy(
+		static_cast<RenderMode::Mode>(ticket_->property("mode").toInt()));
 	const QString decode_filename = use_proxy ? stream->proxy_filename() :
 												stream->filename();
 	const QString decoder_id = use_proxy ? stream->proxy_decoder() :
@@ -613,10 +611,8 @@ void RenderProcessor::process_audio_footage(SampleBuffer &destination,
 
 	// Mirror the video path: use the proxy (when enabled, ready, and containing
 	// audio) for offline renders only, never for export
-	const bool use_proxy =
-		static_cast<RenderMode::Mode>(ticket_->property("mode").toInt()) ==
-			RenderMode::k_offline &&
-		stream->has_proxy() && QFileInfo::exists(stream->proxy_filename());
+	const bool use_proxy = stream->should_use_proxy(
+		static_cast<RenderMode::Mode>(ticket_->property("mode").toInt()));
 	const QString decode_filename = use_proxy ? stream->proxy_filename() :
 												stream->filename();
 	const QString decoder_id = use_proxy ? stream->proxy_decoder() :

app/render/renderworkerpool.cpp

@@ -137,16 +137,18 @@ DecoderPtr resolve_decoder_from_cache(DecoderCache *decoder_cache,
 }
 
 FramePtr decode_input_frame(DecoderCache *decoder_cache,
-						  const FootageInput &input, CancelAtom *cancel)
+						  const FootageInput &input, CancelAtom *cancel,
+						  RenderMode::Mode mode)
 {
 	VideoParams stream_data = input.job.video_params();
 	QString filename = input.job.filename();
 	QString decoder_id = input.job.decoder();
 	int stream_index = stream_data.stream_index();
 
-	// Use generated proxy if one is attached to the job. The Footage node only
-	// attaches a proxy when it is enabled, ready, and matches this stream.
-	if (input.job.has_proxy()) {
+	// Use the generated proxy when this render is allowed to (preview only,
+	// never export). The Footage node only attaches a proxy when it is
+	// enabled, ready, and matches this stream.
+	if (input.job.should_use_proxy(mode)) {
 		filename = input.job.proxy_filename();
 		decoder_id = input.job.proxy_decoder();
 		stream_index = input.job.proxy_stream_index();
@@ -219,7 +221,8 @@ bool decode_input_frames(DecoderCache *decoder_cache,
 			return false;
 		}
 
-		FramePtr frame = decode_input_frame(decoder_cache, input, cancel);
+		FramePtr frame =
+			decode_input_frame(decoder_cache, input, cancel, params.mode);
 		if (!frame || !frame->is_allocated()) {
 			frames->clear();
 			return false;