hardware accelerated ffmpeg hls mosaic

ffgrid.sh

#!/usr/bin/env nix-shell
#!nix-shell --pure -i bash -p ffmpeg-full -p bc -p findutils -p ripgrep

set -euxo pipefail

function join_by {
  local d=$1
  shift
  local f=$1
  shift
  printf %s "$f" "${@/#/$d}"
}

data_dir="$1"
filter="$(mktemp)"
files=($(find "$data_dir" -regextype sed -regex '.*/cam_[0-9]\+\.m3u8' | sort -n))

inputs=()
cams=()
for file in "${files[@]}"; do
  inputs+=(-hwaccel cuvid -hwaccel_output_format cuda -c:v h264_cuvid -i "$file")
  cam=$(rg -o --pcre2 '\d+(?=\.m3u8)' <<<"$file")
  cams+=($cam)
  printf "[$cam:v] scale_npp=1280:720, hwdownload, format=nv12, drawtext=text='$cam': x=0: y=0: fontcolor=white: fontsize=100: box=1: boxcolor=black@0.4: boxborderw=5 [a$cam];" >>"$filter"
done

printf "[a%d]" "${cams[@]}" >>"$filter"

num_inputs="${#files[@]}"
width=$(bc <<<"scale=0; sqrt($num_inputs) + 1")
height=$width

layout=()

for y in $(seq 0 $(((height - 1)))); do
  ys=($(seq 0 $(((y - 1)))))
  if [ "${#ys[@]}" -eq 0 ]; then
    right="0"
  else
    right=$(join_by "+" "${ys[@]/#/h}")
  fi
  for x in $(seq 0 $(((width - 1)))); do
    xs=($(seq 0 $(((x - 1)))))
    if [ "${#xs[@]}" -eq 0 ]; then
      left="0"
    else
      left=$(join_by "+" "${xs[@]/#/w}")
    fi
    layout+=("${left}_${right}")
  done
done

layout_s=$(join_by "|" "${layout[@]}")
printf "xstack=inputs=$num_inputs:layout=$layout_s[out]" >>"$filter"

ffmpeg ${inputs[@]} -c:v h264_nvenc -filter_complex_script "$filter" -map '[out]' -f matroska - | ffplay -i -