Cap transcode-hevc to 8 ffmpeg threads by default

Concurrent transcodes on the 56-core mediaserver were running hot.
Limits each ffmpeg invocation to 8 threads via -threads and x265's
pools= param (libx265 ignores -threads alone). Overridable with
TRANSCODE_THREADS env var.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/transcode-hevc.sh

@@ -20,6 +20,7 @@ DONE_LOG="/var/lib/transcode-hevc/completed.log"
 LOG_FILE="/var/log/transcode-hevc.log"
 CRF="${TRANSCODE_CRF:-24}"
 PRESET="${TRANSCODE_PRESET:-medium}"
+THREADS="${TRANSCODE_THREADS:-8}"
 DRY_RUN="${DRY_RUN:-0}"
 QB_URL="${QB_URL:-http://localhost:8080}"
 
@@ -243,9 +244,11 @@ while IFS= read -r -d '' file; do
     rm -f "$tmp_file"
 
     if "$FFMPEG" -nostdin -y \
+        -threads "$THREADS" \
         -i "$file" \
         -map 0:v:0 -map 0:a -map 0:s? \
         -c:v libx265 -crf "$CRF" -preset "$PRESET" \
+        -x265-params "pools=$THREADS" \
         -c:a copy \
         -c:s copy \
         "$tmp_file" \