Add still_clip(), frames_clip(), audio_concat() - #18
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Three call-by-call primitives for slide/scene assembly: - still_clip(): one image -> a video clip, static or animated by a deterministic Ken Burns pan/zoom (zoompan with eased zoom + anchor expressions, crop clamped to frame). Same encode settings as crossfade_concat() so outputs stay concat-compatible. - frames_clip(): a numbered frame sequence -> a video clip; the landing pad for programmatically drawn animations. - audio_concat(): join audio files through the concat filter with exact anullsrc silences between and after them, normalizing rate/layout; built for assembling a narration bed from per-segment TTS takes.
Since the frame-exact chain (#17), crossfade_concat probed videos[1] unconditionally, so the single-clip dry_run path errored on files that don't exist yet (test_crossfade.R line 6 has been failing since). Only probe when a join, window, or audio overlay actually needs the rate.
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Three call-by-call primitives, the compost half of the slide-explainer pipeline (cornductor's
rmd_to_otiod()) and the landing pad for programmatic frame-drawn animation.still_clip()— one image → a video clip, static or animated by a deterministic Ken Burns pan/zoom. Both cases run the same zoompan path (eased zoom + anchor expressions, crop clamped to frame) and the same encode settings ascrossfade_concat(), so outputs stay concat-compatible. Motion spec:zoom_from/zoom_to/from/to/ease(linear | smooth), tolerant of JSON-deserialized shapes.frames_clip()— a numbered frame sequence → a video clip (-framerate+ pattern input). This is what an OTIOImageSequenceReferencewill lower through in the follow-up renderer PR.audio_concat()— join audio files through the concat filter with exactanullsrcsilences between (gap) and after (tail), normalizing rate/layout per input; built for assembling a narration bed from per-slide TTS takes.Also fixes a latent main breakage: since #17,
crossfade_concat()probedvideos[1]fps unconditionally, so the single-clipdry_runpath (exercised bytest_crossfade.R:6with afile.createfake) errored. The probe is now lazy — only joins, windows, or an audio overlay need the rate.Internals are pure string builders (
.kenburns_filter,.ease_expr,.still_size,.audio_concat_filter) unit-tested without ffmpeg; at_home tests render real testsrc2/sine fixtures and assert frame counts, dimensions, durations, and that Ken Burns actually moves pixels. Full suite: 167/167 with at_home on.Follow-up PR teaches
render_timeline()to pre-render still and image-sequence clips through these, pluscornball.*effect lowering.