otio: write importable OTIO/FCPXML (DaVinci Resolve rejects both)

- available_range declared a zero duration for every clip (the media
  was 'unusable', so Resolve invalidated all of them): it now covers
  the whole media - video clips in the probed frame rate, audio clips
  in the probed sample rate (no more hardcoded 48000/0).
- Gap ranges mixed time bases (a 24 fps block start, a 1.0 trailing
  duration): gaps now stay in the sequence's time base, the trailing
  pad in whole frames.
- Empty sequences (no clips) are skipped, so a lone edited sequence
  exports as a bare Timeline root instead of a SerializableCollection
  Resolve cannot read.
- FCPXML: an asset used on both video and audio tracks now declares
  hasVideo AND hasAudio (the first registration's track kind used to
  hide the other stream); asset durations recover with available_range.

crates/oak-otio/src/fcpxml.rs

@@ -953,6 +953,15 @@ impl ResourceSet {
 				};
 				let src = external.target_url();
 				if self.asset_ids.contains_key(src) {
+					// Already registered from another track: union the
+					// stream flags so a file used on both a video and an
+					// audio track declares hasVideo AND hasAudio (the
+					// first registration's track kind must not hide the
+					// other stream from the importer).
+					if let Some(existing) = self.assets.iter_mut().find(|a| a.src == src) {
+						existing.has_video |= is_video;
+						existing.has_audio |= is_audio;
+					}
 					continue;
 				}
 				let (asset_format_id, asset_duration) = match external.available_range() {

crates/oak-task/src/nodeops.rs

@@ -472,6 +472,19 @@ pub fn footage_video_params(
 	f.video_params(index).map(common_from_node_video)
 }
 
+/// The footage's first audio stream's sample rate (`oaknode_footage_get_
+/// audio_params`), `None` when unprobed or the file has no audio stream.
+pub fn footage_audio_sample_rate(project: &ProjectRef, footage: NodeId) -> Option<i32> {
+	let guard = lock_project(project);
+	let f = guard
+		.graph
+		.get(footage)?
+		.behavior
+		.as_any()?
+		.downcast_ref::<FootageBehavior>()?;
+	f.audio_params(0).map(|a| a.sample_rate)
+}
+
 /// Overwrite (or create) the footage's `index`th video stream parameters
 /// (`oaknode_footage_set_video_params`).
 pub fn footage_set_video_params(

crates/oak-task/src/project/saveotio.rs

@@ -188,30 +188,42 @@ impl SaveOTIOTask {
 
 					let media = nodeops::node_find_input_footage(project, block);
 					if let Some(media) = media {
+						// The available range covers the WHOLE media: start
+						// 0, duration = the media length in the reference's
+						// own time base (the video rate for video clips, the
+						// sample rate for audio clips — OTIO's External-
+						// Reference convention). A zero duration declares
+						// the media unusable and DaVinci Resolve rejects
+						// every clip whose source range falls outside it.
+						let duration_seconds = nodeops::node_length(project, media).to_f64();
 						let available_range = if track_type == TrackType::Video {
-							// OTIO ExternalReference uses the source clips
-							// frame rate (or sample rate) as opposed to the
-							// sequences rate.
-							let (source_frame_rate, duration) =
-								nodeops::footage_video_params(project, media, 0)
-									.map(|vp| {
-										let (num, den) = vp.frame_rate();
-										let rate = if den != 0 {
-											num as f64 / den as f64
-										} else {
-											0.0
-										};
-										(rate, vp.duration() as f64)
-									})
-									.unwrap_or((0.0, 0.0));
+							let source_frame_rate = nodeops::footage_video_params(project, media, 0)
+								.map(|vp| {
+									let (num, den) = vp.frame_rate();
+									if den != 0 {
+										num as f64 / den as f64
+									} else {
+										0.0
+									}
+								})
+								.filter(|rate| *rate > 0.0)
+								.unwrap_or(sequence_rate);
 							TimeRange::new(
 								RationalTime::new(0.0, source_frame_rate),
-								RationalTime::new(duration, source_frame_rate),
+								RationalTime::new(
+									(duration_seconds * source_frame_rate).round(),
+									source_frame_rate,
+								),
 							)
 						} else {
+							let sample_rate = nodeops::footage_audio_sample_rate(project, media)
+								.unwrap_or(48000) as f64;
 							TimeRange::new(
-								RationalTime::new(0.0, 48000.0),
-								RationalTime::new(0.0, 48000.0),
+								RationalTime::new(0.0, sample_rate),
+								RationalTime::new(
+									(duration_seconds * sample_rate).round(),
+									sample_rate,
+								),
 							)
 						};
 
@@ -226,9 +238,12 @@ impl SaveOTIOTask {
 					Some(Composable::Clip(otio_clip))
 				}
 				nodeops::BlockKind::Gap => Some(Composable::Gap(Gap::new(
+					// Gaps live in timeline time: the SEQUENCE rate, for both
+					// fields — a TimeRange mixing bases (a 24 fps start with
+					// a 1.0 duration) is unreadable to strict importers.
 					TimeRange::new(
-						RationalTime::from_rational(block_in_of(project, block), 24.0),
-						RationalTime::from_rational(block_length_of(project, block), 24.0),
+						RationalTime::from_rational(block_in_of(project, block), sequence_rate),
+						RationalTime::from_rational(block_length_of(project, block), sequence_rate),
 					),
 					nodeops::node_label(project, block),
 				))),
@@ -256,14 +271,18 @@ impl SaveOTIOTask {
 		}
 
 		// All OTIO tracks must have the same duration so we add a Gap to
-		// fill the remaining time.
+		// fill the remaining time. Like the gap blocks above, the range
+		// stays in the sequence's time base (duration in whole frames).
 		let duration = track_duration(&otio_track);
 		let duration_seconds = duration.clone().to_seconds();
 		if duration_seconds < max_track_length.to_f64() {
 			let time_left = max_track_length.to_f64() - duration_seconds;
 
 			let gap = Gap::new(
-				TimeRange::new(duration, RationalTime::new(time_left, 1.0)),
+				TimeRange::new(
+					RationalTime::new(0.0, sequence_rate),
+					RationalTime::new((time_left * sequence_rate).round(), sequence_rate),
+				),
 				"",
 			);
 			otio_track.append_child(Composable::Gap(gap));
@@ -353,6 +372,25 @@ impl TaskBehavior for SaveOTIOTask {
 			}
 		}
 
+		// Drop timelines with no clips at all (an empty sequence the user
+		// never touched): DaVinci Resolve's OTIO import expects a single
+		// Timeline root and chokes on a SerializableCollection — skipping
+		// the empty ones lets a lone edited sequence export as a bare
+		// Timeline. FCPXML benefits the same way (no empty <project>s).
+		serialized.retain(|timeline| {
+			timeline.tracks().children().iter().any(|child| {
+				child
+					.as_track()
+					.is_some_and(|track| track.children().iter().any(|b| b.as_clip().is_some()))
+			})
+		});
+		if serialized.is_empty() {
+			task.set_error("Project contains no edited sequences to export.");
+			return Err(Error::Failed(
+				"Project contains no edited sequences to export.".to_string(),
+			));
+		}
+
 		// Write the serialized timelines, dispatching on the format: OTIO
 		// JSON writes a `Timeline` root for one sequence or a
 		// `SerializableCollection` for several; FCPXML writes all timelines

crates/oak-task/tests/saveotio_test.rs

@@ -0,0 +1,305 @@
+// Oak Video Editor - Non-Linear Video Editor
+// Copyright (C) 2026 Oak Team
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Interchange-export correctness (the "DaVinci Resolve imports nothing"
+//! report): the OTIO JSON must declare a usable `available_range` for
+//! every clip (a zero duration rejects the whole file), gap ranges must
+//! stay in the sequence's time base, an edited lone sequence exports as
+//! a bare `Timeline` root (empty sequences are skipped), and the FCPXML
+//! assets of a file used on both video and audio tracks declare both
+//! stream flags.
+
+use std::sync::{Arc, Mutex};
+
+use oak_core::{Rational, TimeRange};
+use oak_node::block::ClipBlockBehavior;
+use oak_node::footage::FootageBehavior;
+use oak_node::id::NodeId;
+use oak_node::node::NodeCore;
+use oak_node::project::Project;
+use oak_node::sequence::SequenceBehavior;
+use oak_node::track::{TrackBehavior, TrackListBehavior, TrackType};
+use oak_otio::{MediaReference, Serializable};
+
+/// The sequence's frame rate (the `set_default_parameters` NTSC
+/// default) every timeline-range must share.
+fn sequence_rate() -> f64 {
+	30000.0 / 1001.0
+}
+
+fn clip_path(tag: &str, ext: &str) -> std::path::PathBuf {
+	std::env::temp_dir().join(format!("oaktask_otio_{tag}_{}.{ext}", std::process::id()))
+}
+
+/// Add a track of `kind` carrying one clip of `footage` covering
+/// `[in, out)` (media seconds) to `list` — the graph plumbing shared by
+/// the two sequences built below.
+fn add_track_with_clip(
+	p: &mut Project,
+	footage: NodeId,
+	kind: TrackType,
+	in_: Rational,
+	out: Rational,
+) -> NodeId {
+	let (tcore, tbehavior) = TrackBehavior::create();
+	let track = p.graph.add_node(tcore, tbehavior);
+	p.graph
+		.get_mut(track)
+		.unwrap()
+		.behavior
+		.as_any_mut()
+		.unwrap()
+		.downcast_mut::<TrackBehavior>()
+		.unwrap()
+		.kind = kind;
+
+	let (ccore, cbehavior) = oak_node::block::clip_create();
+	let clip = p.graph.add_node(ccore, cbehavior);
+	p.graph
+		.connect(footage, clip, oak_node::block::clip_input::TEXTURE_INPUT, -1)
+		.expect("connect footage to clip");
+	p.graph
+		.get_mut(clip)
+		.unwrap()
+		.behavior
+		.as_any_mut()
+		.unwrap()
+		.downcast_mut::<ClipBlockBehavior>()
+		.expect("clip block")
+		.core
+		.range = TimeRange::new(in_, out);
+	p.graph
+		.get_mut(track)
+		.unwrap()
+		.behavior
+		.as_any_mut()
+		.unwrap()
+		.downcast_mut::<TrackBehavior>()
+		.unwrap()
+		.append_block(clip);
+	track
+}
+
+/// A project with two sequences: "Edited" (a 1s video clip on one video
+/// track, a 0.5s video clip on a second — leaving a trailing gap — and
+/// the same media on an audio track) and "Empty" (no tracks). Both sit
+/// in the root folder, like the app's project bin.
+fn build_project(media: &str) -> Arc<Mutex<Project>> {
+	let project = Project::new();
+	{
+		let mut p = project.lock().unwrap();
+		p.initialize().expect("root folder");
+
+		let footage = {
+			let mut f = FootageBehavior::new(media);
+			f.probe().expect("probe the generated clip");
+			p.graph.add_node(NodeCore::new(), Box::new(f))
+		};
+
+		// "Edited": video list (two tracks) + audio list (one track).
+		let (score, sbehavior) = SequenceBehavior::create();
+		let edited = p.graph.add_node(score, sbehavior);
+		{
+			let video_track_a = add_track_with_clip(
+				&mut p,
+				footage,
+				TrackType::Video,
+				Rational::new(0, 1),
+				Rational::new(1, 1),
+			);
+			let video_track_b = add_track_with_clip(
+				&mut p,
+				footage,
+				TrackType::Video,
+				Rational::new(0, 1),
+				Rational::new(1, 2),
+			);
+			let audio_track = add_track_with_clip(
+				&mut p,
+				footage,
+				TrackType::Audio,
+				Rational::new(0, 1),
+				Rational::new(1, 1),
+			);
+			for (kind, tracks) in [
+				(TrackType::Video, vec![video_track_a, video_track_b]),
+				(TrackType::Audio, vec![audio_track]),
+			] {
+				let (lcore, lbehavior) = TrackListBehavior::create();
+				let list = p.graph.add_node(lcore, lbehavior);
+				{
+					let list_b = p
+						.graph
+						.get_mut(list)
+						.unwrap()
+						.behavior
+						.as_any_mut()
+						.unwrap()
+						.downcast_mut::<TrackListBehavior>()
+						.unwrap();
+					list_b.kind = kind;
+					list_b.tracks = tracks;
+				}
+				p.graph
+					.get_mut(edited)
+					.unwrap()
+					.behavior
+					.as_any_mut()
+					.unwrap()
+					.downcast_mut::<SequenceBehavior>()
+					.unwrap()
+					.track_lists
+					.push(list);
+			}
+			p.graph
+				.get_mut(edited)
+				.unwrap()
+				.core
+				.label = "Edited".to_string();
+		}
+
+		// "Empty": a sequence with no track lists at all.
+		let (ecore, ebehavior) = SequenceBehavior::create();
+		let empty = p.graph.add_node(ecore, ebehavior);
+		p.graph.get_mut(empty).unwrap().core.label = "Empty".to_string();
+
+		// Both live in the root folder (the save task enumerates it).
+		let root = p.root;
+		p.graph
+			.get_mut(root)
+			.unwrap()
+			.behavior
+			.as_any_mut()
+			.unwrap()
+			.downcast_mut::<oak_node::folder::FolderBehavior>()
+			.expect("root folder")
+			.children
+			.extend([edited, empty]);
+	}
+	project
+}
+
+/// Run the save task for `project` to `filename`.
+fn save(project: &Arc<Mutex<Project>>, filename: String) {
+	let mut driver = oak_task::task::Task::new("Saving project...", None);
+	driver.set_behavior(Box::new(oak_task::project::saveotio::SaveOTIOTask {
+		base: oak_task::task::Task::new("Saving project...", None),
+		project: project.clone(),
+		filename: filename.clone(),
+	}));
+	if let Err(e) = driver.start() {
+		panic!(
+			"save to {filename} failed: {e:?} / {}",
+			driver.error().unwrap_or("unknown error")
+		);
+	}
+}
+
+/// OTIO JSON: a lone edited sequence exports as a bare `Timeline` root;
+/// every clip declares a usable available range; every gap range is in
+/// the sequence's time base.
+#[test]
+fn otio_export_is_importable() {
+	let media = clip_path("src_otio", "mp4");
+	oak_codec::testmedia::write_test_clip(&media, 64, 64, 10, 10).expect("clip generation");
+	let project = build_project(&media.to_string_lossy());
+	let out = clip_path("out", "otio");
+	let _ = std::fs::remove_file(&out);
+	save(&project, out.to_string_lossy().into_owned());
+
+	let doc = oak_otio::from_json_file(&out).expect("the export parses as OTIO");
+	let Serializable::Timeline(timeline) = doc else {
+		panic!("one edited sequence must export as a bare Timeline root, not a collection");
+	};
+	assert_eq!(timeline.name(), "Edited");
+
+	let mut clips = 0;
+	let mut gaps = 0;
+	for child in timeline.tracks().children() {
+		let track = child.as_track().expect("track");
+		for block in track.children() {
+			if let Some(clip) = block.as_clip() {
+				clips += 1;
+				let range = clip
+					.media_reference()
+					.and_then(MediaReference::as_external_reference)
+					.expect("external reference")
+					.available_range()
+					.expect("available_range");
+				assert!(
+					range.duration().value() > 0.0,
+					"a zero available range rejects the file everywhere"
+				);
+				assert!(range.duration().rate() > 0.0);
+				if track.kind() == "Audio" {
+					assert_eq!(
+						range.duration().rate(),
+						48000.0,
+						"an audio clip's available range is in the media's sample rate"
+					);
+				}
+			}
+			if let Some(gap) = block.as_gap() {
+				gaps += 1;
+				let range = gap.source_range().expect("gap range");
+				assert!(
+					(range.duration().rate() - sequence_rate()).abs() < 1e-6,
+					"gap duration rate {} is not the sequence rate",
+					range.duration().rate()
+				);
+				assert!(
+					(range.start_time().rate() - sequence_rate()).abs() < 1e-6,
+					"gap start rate {} is not the sequence rate",
+					range.start_time().rate()
+				);
+			}
+		}
+	}
+	assert_eq!(clips, 3, "two video clips + one audio clip");
+	assert!(gaps >= 1, "the half-length video track gains a trailing gap");
+
+	let _ = std::fs::remove_file(&media);
+	let _ = std::fs::remove_file(&out);
+}
+
+/// FCPXML: the shared media's single asset declares hasVideo AND
+/// hasAudio, and no asset carries a zero duration.
+#[test]
+fn fcpxml_export_declares_both_streams_and_real_durations() {
+	let media = clip_path("src_fcpxml", "mp4");
+	oak_codec::testmedia::write_test_clip(&media, 64, 64, 10, 10).expect("clip generation");
+	let project = build_project(&media.to_string_lossy());
+	let out = clip_path("out", "fcpxml");
+	let _ = std::fs::remove_file(&out);
+	save(&project, out.to_string_lossy().into_owned());
+
+	let xml = std::fs::read_to_string(&out).expect("read the fcpxml export");
+	assert!(
+		xml.contains("hasVideo=\"1\""),
+		"the shared media's asset declares video: {xml}"
+	);
+	assert!(
+		xml.contains("hasAudio=\"1\""),
+		"the shared media's asset declares audio: {xml}"
+	);
+	assert!(
+		!xml.contains("duration=\"0/1s\""),
+		"no asset carries a zero duration: {xml}"
+	);
+
+	let _ = std::fs::remove_file(&media);
+	let _ = std::fs::remove_file(&out);
+}