tools/guest-diag: tag BGRA capture records as GZF2 fmt 33

sdl_cap.c wrote the same 32 in the GZF2 record format field for every
capture path, so gzf2_video.py's auto mode decoded ARGB8888/X-surface
frames (BGRA byte order on little-endian) as RGBA and swapped red and
blue. Make the field the documented pixel-order tag: 32 = RGBA8 from
the GL swap path (glReadPixels GL_RGBA), 33 = BGRA8 from
SDL_RenderReadPixels(ARGB8888) and X window surfaces; xgrab.c tags its
ZPixmap BGRA records 33 as well.

gzf2_video.py continues to accept both tags (and old all-32 captures
via --pix-fmt bgra), checks ffmpeg/ffprobe before indexing, and keeps
the final resampled endpoint so a 90-frame 60 fps capture encodes as
90 frames instead of 88.

1 files changed, 20 insertions, 5 deletions

diff --git a/tools/guest-diag/gzf2_video.py b/tools/guest-diag/gzf2_video.py
index aa88aa0..8635ca0 100644
--- a/tools/guest-diag/gzf2_video.py
+++ b/tools/guest-diag/gzf2_video.py
@@ -9,9 +9,11 @@
 #
 # Format: [0..8) = "GZCAPV01", zero pad to 4096; then records:
 #   4B "GZF2" | u32 w | u32 h | u32 stride | u32 fmt | u64 ts_ns | u64 seq |
-#   stride*h bytes, top-down.  fmt 32 = RGBA8 (GL swap path), 33 = BGRA8
-#   (SDL_RenderReadPixels ARGB8888 / X surface).  A trailing
-#   "GZF2" + u64 0xffffffffffffffff marks a clean stop.
+#   stride*h bytes, top-down.  fmt is a pixel-order tag: 32 = RGBA8 (GL swap
+#   path, glReadPixels GL_RGBA), 33 = BGRA8 (SDL_RenderReadPixels ARGB8888 /
+#   X surface).  A trailing "GZF2" + u64 0xffffffffffffffff marks a clean stop.
+#   Captures written before the 33 tag existed recorded BGRA paths as 32;
+#   decode those with --pix-fmt bgra.
 #
 # Usage:
 #   gzf2_video.py CAPTURE OUT.mp4 [--fps 60] [--skip 5] [--duration 20]
@@ -22,6 +24,7 @@ import bisect
 import hashlib
 import json
 import os
+import shutil
 import struct
 import subprocess
 import sys
@@ -89,7 +92,13 @@ def pick_frames(recs, fps, skip_s, duration_s):
     cand = [r for r in recs if r["ts"] >= t0] or recs
     ts = [r["ts"] for r in cand]
     span = (ts[-1] - ts[0]) / 1e9
-    n = int(duration_s * fps) if duration_s else max(1, int(span * fps))
+    if duration_s:
+        n = max(1, int(round(duration_s * fps)))
+    else:
+        # Nearest-frame sampling must include both endpoints: a capture that
+        # spans k frame periods yields k+1 output frames (int() alone drops
+        # the last frame and can lose one more to float formatting).
+        n = max(1, int(round(span * fps)) + 1)
     picks, held = [], 0
     for i in range(n):
         want = ts[0] + int(i * 1e9 / fps)
@@ -179,10 +188,16 @@ def main():
                     default="libx264")
     ap.add_argument("--crf", type=int, default=18)
     ap.add_argument("--pix-fmt", choices=["auto", "rgba", "bgra"],
-                    default="auto", help="auto uses record fmt (33=BGRA)")
+                    default="auto",
+                    help="auto uses the record tag (32=RGBA, 33=BGRA); "
+                         "old BGRA captures tagged 32 need bgra")
     ap.add_argument("--info-only", action="store_true")
     args = ap.parse_args()
 
+    for tool in ("ffmpeg", "ffprobe"):
+        if not shutil.which(tool):
+            die(f"{tool} not found in PATH")
+
     recs, clean, corrupt = index_capture(args.capture)
     uniq = len({r["md5"] for r in recs})
     span = (recs[-1]["ts"] - recs[0]["ts"]) / 1e9