path: root/bin/decode+edit+encode

#!/bin/sh

# FIXME: Handle audio

set -e

INPUT=../src/omni/show0/earth.mp4
LOGO=../../content/icon_small.png
OUTPUT=../tmp/omni/show0/earth.webm

##
## generic functions
##
# shellcheck disable=SC2048,SC2059
echo_n() {
 printf -- "$*"
}

HEIGHT=360

SPEED_VP8=4

# * height steps and bitrates based on https://developer.apple.com/library/content/documentation/General/Reference/HLSAuthoringSpec/Requirements.html
# TODO: adjust height steps or bitrates for 4:3 aspect ratio
# TODO: resolve steps from source height using http://aarmstrong.org/tutorials/aspect-ratios-and-h264
if [ $HEIGHT -le 234 ]; then
 VBITRATE=145000
elif [ $HEIGHT -le 270 ]; then
 VBITRATE=365000
elif [ $HEIGHT -le 360 ]; then
 VBITRATE=730000
elif [ $HEIGHT -le 432 ]; then
 VBITRATE=1100000
elif [ $HEIGHT -le 540 ]; then
 VBITRATE=2000000
elif [ $HEIGHT -le 720 ]; then # 720p → 921600
 VBITRATE=3000000
fi

encode_vp8() { bitrate=$1; speed=$2;
 echo_n "-codec:v vp8 -quality realtime -deadline 1000000 -cpu-used $speed \
 -b:v $bitrate -minrate $bitrate -maxrate $bitrate \
 -undershoot-pct 95 -bufsize $((6000*bitrate/1000)) -rc_init_occupancy $((4000*bitrate/1000)) \
 -max-intra-rate 0 \
 -qmin 4 -qmax 56"
}

mkdir -p $(dirname "$OUTPUT")

# based on http://www.webmproject.org/docs/encoder-parameters/#real-time-cbr-encoding-and-streaming
# + scale+watermark trick based on http://stackoverflow.com/a/10937357
# + scale to square pixels as needed
# + Add 1s latency (deadline)
ffmpeg -hide_banner -threads auto -y -re \
 -i "$INPUT" \
 -i "$LOGO" \
 -filter_complex \
 "[0:v]format=pix_fmts=yuv420p,scale=iw*sar*$HEIGHT/ih:$HEIGHT,setsar=1[bg];
  [bg][1:v]overlay=main_w-overlay_w-20:main_h-overlay_h-20[v]" \
 -map '[v]' \
 $(encode_vp8 "$VBITRATE" "$SPEED_VP8") \
 -f webm "$OUTPUT"