refactor(core): combine ffprobe calls and simplify pixel format selection

Merge the two separate ffprobe invocations for codec and pixel format
into one, halving the per-file probe overhead on large batches. Both
error messages now include the filename for easier diagnosis in batch
runs.

Replace the three-way nested if/elif/else for pixel format selection
with two independent case statements — one for chroma subsampling, one
for bit depth — that compose the output format string from two parts.
This eliminates the repetition across the three subsampling branches
and makes adding a new bit depth or subsampling variant a single-line
change. Also add a verbose fallback warning for exotic formats that
don't match any known subsampling pattern.

1 files changed, 37 insertions, 43 deletions

diff --git a/transcode.sh b/transcode.sh
index 6b0bb22..436c89f 100755
--- a/transcode.sh
+++ b/transcode.sh
@@ -632,25 +632,31 @@ encode_one() {
     return $EXIT_RUNTIME_FAILURE
   }
 
-  local input_codec
-  input_codec=$(ffprobe -v error -select_streams v:0 -show_entries stream=codec_name -of default=nk=1:nw=1 "file:$file" 2>/dev/null)
+  # Probe codec and pixel format in a single ffprobe invocation to halve
+  # the startup overhead on large batches.
+  local probe_out
+  probe_out=$(ffprobe -v error -select_streams v:0 \
+    -show_entries stream=codec_name,pix_fmt \
+    -of default=nk=1:nw=1 "file:$file" 2>/dev/null)
+
+  local input_codec input_pixel_format
+  input_codec=$(printf '%s\n' "$probe_out" | sed -n '1p')
+  input_pixel_format=$(printf '%s\n' "$probe_out" | sed -n '2p')
+
   if [[ -z "$input_codec" ]]; then
-    error "Could not determine input video codec"
+    error "Could not determine input video codec:" "$file"
+    return $EXIT_RUNTIME_FAILURE
+  fi
+  if [[ -z "$input_pixel_format" ]]; then
+    error "Could not determine input pixel format:" "$file"
     return $EXIT_RUNTIME_FAILURE
   fi
 
   if [[ -v SKIP_CODECS["$input_codec"] ]]; then
-    msg "Skip because of input codec:" "$input_codec"
+    msg "Skipping (codec excluded):" "$input_codec"
     return $EXIT_OK
   fi
 
-  local input_pixel_format
-  input_pixel_format=$(ffprobe -v error -select_streams v:0 -show_entries stream=pix_fmt -of default=nk=1:nw=1 "file:$file" 2>/dev/null)
-  if [[ -z "$input_pixel_format" ]]; then
-    error "Could not determine input pixel format"
-    return $EXIT_RUNTIME_FAILURE
-  fi
-
   # Some files report "yuvj*" formats (full-range JPEG-style). For encoding
   # purposes we normalize to the equivalent "yuv*" formats.
   input_pixel_format="${input_pixel_format/yuvj/yuv}"
@@ -660,38 +666,26 @@ encode_one() {
   # to avoid unintended quality loss or incompatible output.
   # Known limitation: exotic formats not matching these patterns (e.g. gbrp,
   # yuva*, gray*) fall through to yuv420p. Extend the logic below if needed.
-  local output_pixel_format
-  if [[ "$input_pixel_format" == *"444"* ]]; then
-    if [[ "$input_pixel_format" == *"16"* ]]; then
-      output_pixel_format="yuv444p16le"
-    elif [[ "$input_pixel_format" == *"12"* ]]; then
-      output_pixel_format="yuv444p12le"
-    elif [[ "$input_pixel_format" == *"10"* ]]; then
-      output_pixel_format="yuv444p10le"
-    else
-      output_pixel_format="yuv444p"
-    fi
-  elif [[ "$input_pixel_format" == *"422"* ]]; then
-    if [[ "$input_pixel_format" == *"16"* ]]; then
-      output_pixel_format="yuv422p16le"
-    elif [[ "$input_pixel_format" == *"12"* ]]; then
-      output_pixel_format="yuv422p12le"
-    elif [[ "$input_pixel_format" == *"10"* ]]; then
-      output_pixel_format="yuv422p10le"
-    else
-      output_pixel_format="yuv422p"
-    fi
-  else
-    if [[ "$input_pixel_format" == *"16"* ]]; then
-      output_pixel_format="yuv420p16le"
-    elif [[ "$input_pixel_format" == *"12"* ]]; then
-      output_pixel_format="yuv420p12le"
-    elif [[ "$input_pixel_format" == *"10"* ]]; then
-      output_pixel_format="yuv420p10le"
-    else
-      output_pixel_format="yuv420p"
-    fi
-  fi
+  local subsampling depth output_pixel_format
+
+  case "$input_pixel_format" in
+  *444*) subsampling="444" ;;
+  *422*) subsampling="422" ;;
+  *)
+    subsampling="420"
+    [[ "$input_pixel_format" != *420* ]] &&
+      verbose "Unrecognised chroma subsampling in '$input_pixel_format', falling back to yuv420p"
+    ;;
+  esac
+
+  case "$input_pixel_format" in
+  *16*) depth="p16le" ;;
+  *12*) depth="p12le" ;;
+  *10*) depth="p10le" ;;
+  *) depth="p" ;;
+  esac
+
+  output_pixel_format="yuv${subsampling}${depth}"
   debug "Selected output pixel format:" "$output_pixel_format"
 
   # Load preset early so a missing/invalid preset fails before we create a