fix(capture): working All-Intra HEVC NVENC config (validated on L4)

NVENC rejects -g 1 ("GopLength > numBFrames+1" at InitializeEncoder), so
true all-intra is achieved with -bf 0 -forced-idr 1 -g 600 plus
-force_key_frames expr:1 (forces an IDR on every frame). ffprobe confirms
all frames are pict_type=I. Container is fragmented MOV; MXF muxing of HEVC
fails on this ffmpeg build ("Operation not permitted").

Validated end-to-end via direct ffmpeg on zampp2/L4:
hevc, Main 10, 1920x1080, yuv420p10le, ptypes=[IIIIII...]

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/capture/src/capture-manager.js

@@ -29,15 +29,28 @@ const VIDEO_CODECS = {
   h264_nvenc:   { args: ['-c:v', 'h264_nvenc', '-preset', 'p5'],    bitrateControl: true,  pixFmt: 'yuv420p' },
   h265:         { args: ['-c:v', 'libx265', '-preset', 'medium'],   bitrateControl: true,  pixFmt: 'yuv420p' },
   // All-Intra HEVC on NVENC — the growing-file master codec.
-  // -g 1 -bf 0: every frame is an IDR (all-intra), no B-frames.
+  // Goal: every frame an IDR (all-intra), so a still-growing file is decodable
-  //   Required for growing-file edit-while-record (partial file must be
+  // to its last complete frame — the prerequisite for edit-while-record.
-  //   decodable to the last complete frame without a full GOP).
+  //
-  // -rc vbr: variable bitrate; pair with a high target bitrate (100–160 Mbps
+  // NVENC will NOT accept `-g 1`: InitializeEncoder enforces
-  //   for 1080i) to rival ProRes HQ quality.
+  // "GopLength > numBFrames + 1", so with -bf 0 the minimum GOP is 2 and -g 1
-  // -profile:v main10 / p010le: 10-bit 4:2:0 — the closest NVENC HEVC can
+  // is rejected with EINVAL (validated on the L4, driver 595). The working
-  //   get to ProRes 4:2:2 10-bit. If strict 4:2:2 is needed, use prores_hq.
+  // recipe for true all-intra is therefore:
+  //   -bf 0              no B-frames
+  //   -g 600             large GOP just to satisfy the init check
+  //   -forced-idr 1      forced keyframes are emitted as IDR
+  //   -force_key_frames expr:1   force a keyframe on EVERY frame
+  // → ffprobe confirms pict_type = I for all frames.
+  //
+  // Container: fragmented MOV (+frag_keyframe+empty_moov+default_base_moof),
+  // NOT MXF — this ffmpeg's MXF muxer rejects HEVC ("Operation not permitted").
+  // The frag-MOV index is not deferred to EOF, so the file stays readable while
+  // growing. (See docs/design/2026-05-29-all-intra-hevc-ingest.md §8.)
+  //
+  // -profile:v main10 / p010le: 10-bit 4:2:0 — the closest NVENC HEVC can get
+  // to ProRes 4:2:2 10-bit. If strict 4:2:2 is required, use prores_hq (CPU).
   hevc_nvenc:   {
-    args: ['-c:v', 'hevc_nvenc', '-preset', 'p4', '-rc', 'vbr', '-g', '1', '-bf', '0', '-profile:v', 'main10'],
+    args: ['-c:v', 'hevc_nvenc', '-preset', 'p4', '-rc', 'vbr', '-bf', '0', '-forced-idr', '1', '-g', '600', '-force_key_frames', 'expr:1', '-profile:v', 'main10'],
     bitrateControl: true,
     pixFmt: 'p010le',
   },