test render script can cut without desync

230101/setup.sh

+#!/bin/busybox ash
+set -euo pipefail
+
+for i in 1 2 3; do rm "C0$i.svg" || true; rm "C0$i.mp4" || true; done
+
+function write_svg() {
+	echo '<svg viewBox="0 0 1920 1080" width="1920" height="1080">'
+	echo '  <rect fill="'"$1"'" x="0" y="0" width="1920" height="1080"/>'
+	echo '</svg>'
+}
+
+write_svg blue  >C01.svg
+write_svg green >C02.svg
+write_svg red   >C03.svg
+
+function render_svg() {
+	ffmpeg -hide_banner -vaapi_device /dev/dri/renderD128 \
+		-loop 1 -i "$1" \
+		-filter_complex "[0]format=nv12,hwupload[v];aevalsrc=sin($3*2*PI*t):s=48000[a]" \
+		-map "[v]" -map "[a]" \
+		-c:v h264_vaapi -r 25 -t 4 -b:a 128000 "$2"
+}
+
+for i in 1 2 3; do render_svg "C0$i.svg" "C0$i.mp4" $(($i*40+400)); done

230101/test_render.sh

+#!/bin/busybox ash
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+lecture=test_render
+mkdir -p "$lecture"
+rm "$lecture"/* || true
+
+for file in *.mp4; do echo "file '$(realpath "$file")'" >>"$lecture/recording.txt"; done
+
+function write_svg() {
+	echo '<svg viewBox="0 0 1920 1080" width="1920" height="1080">'
+	echo '  <rect fill="black" x="0" y="0" width="1920" height="1080"/>'
+	echo '  <text x="960" y="540" fill="white" text-anchor="middle" dominant-baseline="hanging" font-family="Noto Sans">'
+	echo "    $1"
+	echo '  </text>'
+	echo '</svg>'
+}
+
+write_svg Intro >"$lecture/intro.svg"
+write_svg Outro >"$lecture/outro.svg"
+
+set -x
+
+ffmpeg \
+	-hide_banner \
+	-f concat \
+	-safe 0 \
+	-i "$lecture/recording.txt" \
+	-af "pan=stereo|c0=c0|c1=c0,aformat=sample_rates=48000" \
+	-c:v copy -b:a 128000 \
+	"$lecture/recording.mp4"
+
+ffmpeg \
+	-hide_banner \
+	-vaapi_device /dev/dri/renderD128 \
+	-loop 1 -i "$lecture/intro.svg" \
+	-filter_complex "[0]format=nv12,hwupload[v];aevalsrc=0:s=48000[a]" \
+	-map "[v]" -map "[a]" \
+	-c:v h264_vaapi -r 25 -t 3 -b:a 128000 \
+	"$lecture/intro.mp4"
+
+ffmpeg \
+	-hide_banner \
+	-vaapi_device /dev/dri/renderD128 \
+	-loop 1 -i "$lecture/outro.svg" \
+	-filter_complex "[0]format=nv12,hwupload[v];aevalsrc=0:s=48000[a]" \
+	-map "[v]" -map "[a]" \
+	-c:v h264_vaapi -r 25 -t 5 -b:a 128000 \
+	"$lecture/outro.mp4"
+
+ffmpeg \
+	-hide_banner \
+	-vaapi_device /dev/dri/renderD128 \
+	-i "$lecture/intro.mp4" \
+	-i "$lecture/recording.mp4" \
+	-i "$lecture/outro.mp4" \
+	-i "../assets/logo.svg" \
+	-i "../assets/fastforward.svg" \
+	-async 1 \
+	-filter_complex "
+			[1:v]trim=start=2:duration=8,setpts=PTS-STARTPTS[v_tmp0];
+			[1:a]atrim=start=2:duration=8,asetpts=PTS-STARTPTS[a_tmp0];
+			[0:v][0:a][v_tmp0][a_tmp0][2:v][2:a]concat=n=3:v=1:a=1[v_tmp1][a_tmp1];
+			[v_tmp1]format=nv12,hwupload[final_v];
+			[a_tmp1]anull[final_a]
+		" \
+	-map '[final_v]' -map '[final_a]' \
+	-c:v h264_vaapi -rc_mode CQP -global_quality 22 \
+	-c:a aac -b:a 128000 \
+	"$lecture/$lecture.mp4"