iter4 Phase 6: 4 commits landed (Z+A+B+C), ffmpeg-vaapi VP9 decode PASS
Fork at marfrit/libva-multiplanar tip beaa914: - Z (7f8fa93) device-path auto-detect via media controller topology; walk /dev/media*, MEDIA_IOC_DEVICE_INFO match, MEDIA_IOC_G_TOPOLOGY -> MEDIA_INTF_T_V4L_VIDEO -> resolve via /sys/dev/char. LIBVA_V4L2_REQUEST_NO_AUTODETECT=1 escape hatch. - A (16b3973) src/config.c VP9 enumeration + dispatch + entrypoints. - B (406d08e) NEW src/vp9.c (~750 LOC: VPX rac + inv_map_table + uncompressed-header partial parser + compressed-header parser + vp9_set_controls) + src/vp9.h + meson.build + context.h (persistent vp9_lf state for Phase 5 C2) + surface.h (params.vp9 union extension). - C (beaa914) src/picture.c VP9 dispatcher + 2 buffer-type cases. NO Commit D — buffer.c allow-list already permissive for VP9's 3 buffer types (Picture, Slice, SliceData; all in iter3 baseline). Phase 5 amendments all in code: C1 no-XOR direct, C2 persistent vp9_lf with VP9 spec defaults, C3 out_reference_mode parameter, C4 NO_AUTODETECT escape, S4 uv_mode memcpy omitted. Plan amendment to Commit Z section in phase4_iter4_plan.md documents the canonical media-topology approach (replacing the original /dev/video* walk). Verification empirically on fresnel: - Criterion 1: vainfo enumerates VAProfileVP9Profile0 alongside H.264 + HEVC under auto-detect rkvdec. - Criterion 2 (implicit via successful ffmpeg run). - Criterion 3: ffmpeg-vaapi VP9 5-frame decode exit 0 at 0.307x speed, no ioctl errors. - Criterion 4: deferred to Phase 7 verification. - Criterion 5: rkvdec codecs work without env override; hantro (MPEG-2/VP8) still need env override per iter4-B1 backlog. Open iter4 backlog: B1 (multi-decoder dispatch refactor), B2 (mpv-vaapi Could-not-create-device — ffmpeg-vaapi works fine through same backend, mpv does not), Q6 (per-segment ALT_Q mapping for non-BBB), COLOR_RANGE (VAAPI gap). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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@@ -391,70 +391,59 @@ vp9_parse_uncompressed_header_lf_quant(
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iter4 implements as 5 commits (mitigation B + iter3-style ABCD):
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### Commit Z — `src/request.c`: device-path enumeration (mitigation B)
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### Commit Z — `src/request.c`: device-path auto-detect via media-controller topology (mitigation B, canonical form)
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Replace hardcoded `/dev/video0` + `/dev/media0` defaults with walk-and-pick-first-known-decoder:
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**Approach correction (post-implementation user redirect)**: the original plan walked `/dev/video0..15` + matched by `VIDIOC_QUERYCAP` driver name, then paired media node via a separate scan. This is brittle: dependence on enumeration order + assumption that video↔media pairing follows /dev/* numbering. The canonical v4l2-request discovery path drives discovery from the media controller graph instead (which is what FFmpeg's v4l2-request does):
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```c
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static int find_codec_device(char video_path[32], char media_path[32])
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{
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static const char * const known_drivers[] = {
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"rkvdec", "hantro-vpu", "cedrus", "sun4i_csi", NULL
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};
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char path[32];
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struct v4l2_capability caps;
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int fd, i;
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const char * const *kd;
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/* Algorithm:
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* 1. Walk /dev/media0..15. MEDIA_IOC_DEVICE_INFO names the driver.
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* Match against {rkvdec, hantro-vpu, cedrus, sun4i_csi}.
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* 2. MEDIA_IOC_G_TOPOLOGY enumerates the entity/interface graph.
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* The MEDIA_INTF_T_V4L_VIDEO interface carries major:minor of
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* the V4L2 video node owned by THIS media controller — paired
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* by the kernel, NOT by /dev/* enumeration order.
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* 3. Resolve major:minor to /dev/videoN via /sys/dev/char/<M>:<N>
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* (the kernel's char-device sysfs symlink whose basename is
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* the device node name).
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*/
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static int find_codec_device(char *video_out, size_t video_out_sz,
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char *media_out, size_t media_out_sz);
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static int find_video_node_via_topology(int media_fd, char *video_out, size_t out_sz);
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static int resolve_dev_node(uint32_t major, uint32_t minor, char *out, size_t out_sz);
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```
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/* Walk /dev/video0..15 */
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for (i = 0; i < 16; i++) {
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snprintf(path, sizeof path, "/dev/video%d", i);
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fd = open(path, O_RDWR | O_NONBLOCK);
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if (fd < 0) continue;
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if (ioctl(fd, VIDIOC_QUERYCAP, &caps) == 0) {
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for (kd = known_drivers; *kd; kd++) {
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if (strcmp((char *)caps.driver, *kd) == 0) {
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strncpy(video_path, path, 32);
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/* Match media device by driver name */
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find_media_for_driver((char *)caps.driver, media_path);
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close(fd);
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return 0;
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}
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}
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}
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close(fd);
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}
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return -1;
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}
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In `RequestInit`:
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/* In RequestInit (Phase 5 C4 amendment — escape hatch for legacy callers): */
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```c
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if (getenv("LIBVA_V4L2_REQUEST_NO_AUTODETECT")) {
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/* Skip walk; old hardcoded behavior. Lets test automation that
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* relied on /dev/video0 opt out of the new auto-detect logic. */
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video_path = "/dev/video0";
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video_path = "/dev/video0"; /* legacy escape hatch */
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media_path = "/dev/media0";
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} else {
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video_path = getenv("LIBVA_V4L2_REQUEST_VIDEO_PATH");
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if (video_path == NULL) {
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static char auto_video[32], auto_media[32];
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if (find_codec_device(auto_video, auto_media) == 0) {
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if (find_codec_device(auto_video, sizeof auto_video,
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auto_media, sizeof auto_media) == 0) {
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video_path = auto_video;
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if (getenv("LIBVA_V4L2_REQUEST_MEDIA_PATH") == NULL)
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media_path = auto_media;
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auto_media_set = true;
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request_log("auto-selected codec device: %s + %s\n",
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video_path, media_path);
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auto_video, auto_media);
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} else {
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video_path = "/dev/video0"; /* fall back to legacy default */
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video_path = "/dev/video0";
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}
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}
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}
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```
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`find_media_for_driver` walks `/dev/media0..15`, opens each, calls `MEDIA_IOC_DEVICE_INFO`, returns the path whose `driver` field matches. Phase 3 baseline confirmed `media0 ↔ rkvdec` and `media1 ↔ hantro-vpu` on 7.0.
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Predicted +152 LOC, 1 file modified. Build target after Commit Z: `vainfo` (no env) lists the auto-selected decoder's profiles, paired correctly via topology graph. Independent of VP9 — can be tested + merged before Commit A.
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Predicted +35 LOC, 1 file modified. Build target after Commit Z: `vainfo` (no env override) lists the auto-selected decoder's profiles. Independent of VP9 work — can be tested + merged before Commit A.
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**End-user UX gap (documented, NOT fixed in iter4)**: backend opens ONE codec device at init. If user wants the OTHER decoder (default selects rkvdec; user wants hantro for MPEG-2/VP8), they still need env override. Aggregating BOTH decoders simultaneously requires multi-fd dispatch refactor; out of iter4 scope, cross-cutting backlog item iter4-B1.
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**End-user UX gap (documented, NOT fixed in iter4)**: backend opens ONE codec device at init. If user wants the OTHER decoder (e.g., default selects rkvdec but user wants hantro for MPEG-2/VP8), they still need env override. Aggregating BOTH decoders simultaneously requires a deeper refactor (multi-fd dispatch); out of iter4 scope, cross-cutting backlog item iter4-B1.
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**Verified on fresnel `7.0.0-fresnel-fourier` post-Phase-6**:
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- `vainfo` (no env) → `auto-selected codec device: /dev/video1 + /dev/media0`, enumerates H.264×5 + HEVCMain (rkvdec) — pair came from topology graph, not from /dev/* numbering.
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- `vainfo NO_AUTODETECT=1` → empty list (legacy /dev/video0 = rga).
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- `vainfo` with explicit `/dev/video3` + `/dev/media1` → MPEG-2×2 + VP8.
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### Commit A — `src/config.c`: VP9 enumeration + dispatch + entrypoints
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@@ -0,0 +1,97 @@
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# Iteration 4 — Phase 6 (implementation)
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Commits Z + A + B + C landed against fork tip `e1aca9c` (iter3 close). All built clean on fresnel `linux-fresnel-fourier 7.0-1` (libva 1.23, ninja-1.13.2, gcc 15.2.1). No fix-forward Commit D needed — buffer.c allow-list was already permissive for the 3 VAAPI buffer types VP9 uses.
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## Commits
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| SHA | Files | LOC | Summary |
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|---|---|---|---|
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| `7f8fa93` | `src/request.c` | +152 / -4 | Commit Z — device-path auto-detect via media controller topology. Walk `/dev/media*`, `MEDIA_IOC_DEVICE_INFO` → driver match, `MEDIA_IOC_G_TOPOLOGY` → `MEDIA_INTF_T_V4L_VIDEO` interface → resolve major:minor via `/sys/dev/char/<M>:<N>` symlink. Canonical v4l2-request discovery; not enumeration-order dependent. `LIBVA_V4L2_REQUEST_NO_AUTODETECT=1` escape hatch for legacy callers. |
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| `16b3973` | `src/config.c` | +15 | Commit A — VP9 enumeration + dispatch + entrypoints (3 sites). |
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| `406d08e` | `src/vp9.c` (new), `src/vp9.h` (new), `src/meson.build`, `src/context.h`, `src/surface.h` | +810 / -2 | Commit B — VP9 backend: 12 contract clauses, VPX range coder, inv_map_table, uncompressed-header partial parser, compressed-header parser, persistent `vp9_lf` state in object_context. Phase 5 C1+C2+C3 amendments + S4 baked in. Compile-time `_Static_assert` on struct sizes 168/2040. |
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| `beaa914` | `src/picture.c` | +19 | Commit C — VP9 dispatcher + 2 buffer-type cases (Picture, Slice). No `RequestBeginPicture` reset (VP9 has no iqmatrix_set-style flag). |
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**Total**: 4 commits, 996 LOC delta, 7 files (2 new + 5 modified). No Commit D.
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## Verification on fresnel
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### Substrate
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```
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Linux fresnel 7.0.0-fresnel-fourier #1 SMP PREEMPT
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/usr/lib/dri/v4l2_request_drv_video.so SHA256
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f2ff65982a777b64f3392fa6be13b934d969068a1309d24364d99708462c04ee
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```
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### Criterion 1 — vainfo enumerates VAProfileVP9Profile0
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```
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$ LIBVA_DRIVER_NAME=v4l2_request vainfo
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v4l2-request: auto-selected codec device: /dev/video1 + /dev/media0
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vainfo: VA-API version: 1.23 (libva 2.22.0)
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vainfo: Driver version: v4l2-request
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vainfo: Supported profile and entrypoints
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VAProfileH264Main : VAEntrypointVLD
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VAProfileH264High : VAEntrypointVLD
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VAProfileH264ConstrainedBaseline: VAEntrypointVLD
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VAProfileH264MultiviewHigh : VAEntrypointVLD
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VAProfileH264StereoHigh : VAEntrypointVLD
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VAProfileHEVCMain : VAEntrypointVLD
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VAProfileVP9Profile0 : VAEntrypointVLD ← NEW
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```
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Auto-detect (no env override) successfully picked rkvdec via media topology graph. **PASS**.
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### Criterion 2 — vaCreateConfig SUCCESS
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Implicit in successful ffmpeg-vaapi run below. **PASS**.
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### Criterion 3 — ffmpeg-vaapi VP9 decode exit 0
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```
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$ LIBVA_DRIVER_NAME=v4l2_request ffmpeg -hwaccel vaapi -hwaccel_device /dev/dri/renderD128 \
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-i ~/fourier-test/bbb_720p10s_vp9.webm -frames:v 5 -f null -
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v4l2-request: cap_pool_init: 24 slots ready (v4l2_index=0..23, 1 plane(s) per slot)
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[...]
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frame= 5 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.20 bitrate=N/A speed=0.307x
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```
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5 frames decoded at 0.307x speed. Zero kernel ioctl errors. cap_pool_init successful. **PASS**.
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### Criterion 4 — HW=SW byte-identical (deferred to Phase 7)
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Phase 7 will run mpv VP9 capture vs the Phase 3 SW reference PNGs and compare hashes. mpv's vaapi-init path needs investigation (iter4-B2 — does not currently engage HW even with `LIBVA_DRIVER_NAME` set, while ffmpeg-vaapi does). Workaround for criterion 4: use ffmpeg-vaapi-hwdownload path to PNG instead of mpv-vaapi-copy, OR use the iter3-style transitive proof (kernel-direct == backend-payload).
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### Criterion 5 — 4-codec regression block
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H.264 + HEVC (rkvdec via auto-detect): Commit Z restored device-path baseline. Profiles enumerate cleanly without env override.
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MPEG-2 + VP8 (hantro): require `LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video3 LIBVA_V4L2_REQUEST_MEDIA_PATH=/dev/media1` env override (Phase 5 C4 known scope limitation; iter4-B1 backlog).
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Engagement-status verification deferred to Phase 7.
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## Phase 5 amendments status (post-Phase 6)
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| ID | Amendment | Implementation status |
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|---|---|---|
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| C1 | `frame.interpolation_filter = picture->mcomp_filter_type` (no XOR) | `vp9.c::vp9_set_controls` line near "Phase 5 C1: NO XOR" comment |
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| C2 | Persistent `vp9_lf` state in `object_context`, init `{1,0,-1,-1,0,0}` on key/intra/error_res, parse-and-update only on `lf_delta.update=1`, always copy | `context.h` struct `vp9_lf`; `vp9.c::vp9_set_controls` Clause 6 block |
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| C3 | `vp9_fill_compressed_hdr` takes `uint8_t *out_reference_mode`; `allowcompinter` derived from sign biases | `vp9.c::vp9_fill_compressed_hdr` signature + caller derivation |
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| C4 | `LIBVA_V4L2_REQUEST_NO_AUTODETECT=1` escape hatch | `request.c::VA_DRIVER_INIT_FUNC` |
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| S4 | uv_mode memcpy omitted (rkvdec reads from kernel persistent table) | `vp9.c::vp9_fill_compressed_hdr` ends without memcpy |
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## Cross-cutting backlog updates
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- **iter4-B1** (open) Walk-and-pick-first selects rkvdec on RK3399 (its media controller enumerates first); hantro codecs still need explicit env override. Multi-decoder dispatch refactor required.
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- **iter4-B2** (open) mpv-vaapi `Could not create device` failure — appears to be in mpv's libva-DRM device-init path, not in our backend. ffmpeg-vaapi works fine through the same backend; mpv does not. Investigate in Phase 7 if criterion 4 verification needs a mpv path.
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- **iter4-Q6** (open) Per-segment `seg_param[s].luma_ac_quant_scale` → kernel `feature_data[s][ALT_Q]` mapping is fundamentally lossy for non-BBB segmentation-enabled streams. BBB has segmentation disabled so dead code there.
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- **iter4-COLOR_RANGE** (open) VAAPI doesn't expose `color_range`; backend leaves `V4L2_VP9_FRAME_FLAG_COLOR_RANGE_FULL_SWING` clear (BT.709 limited). Wrong for full-range JPEG-encoded VP9.
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## Substrate state at Phase 6 close
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- Fork at iter4 Commit C tip `beaa914` on noether + fresnel `~/src/libva-v4l2-request-fourier/` + `/usr/lib/dri/v4l2_request_drv_video.so`.
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- `vainfo` (auto-detect rkvdec) lists VAProfileVP9Profile0.
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- ffmpeg-vaapi VP9 decode: criterion 3 PASS empirically.
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- mpv-vaapi VP9 still SW-fallback (iter4-B2; not blocking criterion 3).
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- Kernel: `linux-fresnel-fourier 7.0-1`. Same as Phase 3.
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- Fork ready for Phase 7 verification (HW=SW + regression).
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