#!/usr/bin/env php
<?php

// Squishes given video input into sub-4000kb .mp4
// Crops to 16:9
// Strips audio
// HDR to SDR tonemapping
// Picks bitrate to match
// Picks resolution based on bitrate target
// 2-pass encoding with libx264 veryslow

$args = $_SERVER['argv'];
$self = array_shift( $args );

if ( count ( $args ) < 2 ) {
    die( "Usage: $self <srcfile.mp4> <destfile.mp4>\n" );
}
[ $src, $dest ] = $args;
convert( $src, $dest );
exit(0);

//

function run( $cmd, $args ) {
    $commandLine = implode( ' ',
        array_merge(
            [ escapeshellcmd( $cmd ) ],
            array_map( 'escapeshellarg', $args )
        )
    );

    echo "$commandLine\n";
    $output = shell_exec( $commandLine );
    if ( $output === false ) {
        throw new Error( "Failed to run $cmd" );
    }

    return $output;
}

function ffprobe( $path ) {
    $output = run( 'ffprobe', [
        '-hide_banner',
        '-show_format',
        '-show_streams',
        '-print_format',
        'json',
        '--',
        $path
    ] );

    $data = json_decode( $output );
    if ( $data === null ) {
        throw new Error( "Failed to read JSON from ffprobe: $output" );
    }

    return $data;
}

function evenize( $n ) {
    $n = ceil( $n );
    if ( $n & 1 ) {
        $n++;
    }
    return $n;
}

function convert( $src, $dest ) {
    $maxBits = 4000 * 1000 * 8; // fit in 4Mb
    $maxBits = $maxBits * 7 / 8; // leave some headroom

    $probe = ffprobe( $src );

    $videoTracks = array_filter( $probe->streams, function ( $stream ) {
        return $stream->codec_type === 'video';
    } );
    $track = $videoTracks[0];

    $duration = floatval( $track->duration );
    $width = $track->width;
    $height = $track->height;
    $hdr = $track->color_primaries === 'bt2020'; 
    $keyframeInt = ceil( $duration * 60 );

    $bitrate = floor( $maxBits / $duration );

    $mbits = 1000 * 1000;
    if ( $bitrate < 2 * $mbits ) {
        $cropWidth = 854;
        $scaleHeight = 480;
    } else if ( $bitrate <= 4 * $mbits ) {
        $cropWidth = 1280;
        $scaleHeight = 720;
    } else {
        $cropWidth = 1920;
        $scaleHeight = 1080;
    }
    $scaleWidth = evenize( $width * $scaleHeight / $height );

    $filters = [ "scale=w=$scaleWidth:h=$scaleHeight" ];
    if ( $hdr ) {
        $filters[] = "zscale=t=linear:p=bt709";
        $filters[] = "tonemap=hable";
        $filters[] = "zscale=t=bt709:m=bt709:r=full";
    }
    $filters[] = "format=yuv420p";
    $filters[] = "crop=w=$cropWidth";
    $vf = implode( ',', $filters );

    run( 'ffmpeg', [
        '-i', $src,
        '-f', 'null',
        '-vf', $vf,
        '-c:v', 'libx264',
        '-b:v', $bitrate,
        '-preset', 'veryslow',
        '-pass', '1',
        '-g', $keyframeInt,
        '-an',
        '-y', '/dev/null'
    ] );
    run( 'ffmpeg', [
        '-i', $src,
        '-vf', $vf,
        '-c:v', 'libx264',
        '-b:v', $bitrate,
        '-preset', 'veryslow',
        '-pass', '2',
        '-g', $keyframeInt,
        '-an',
        '-y', $dest
    ] );
}

/*
# <18s
ffmpeg \
  -i "yikes.mp4" \
  -f null \
  -vf "zscale=t=linear:p=bt709,\
       tonemap=hable,\
       zscale=w=1146:h=480:t=bt709:m=bt709:r=full,format=yuv420p,\
       crop=w=854" \
  -vcodec libx264 \
  -b:v 1250k \
  -preset veryslow \
  -pass 1 \
  -g 1080 \
  -an \
  -y /dev/null && \
ffmpeg \
  -i "yikes.mp4" \
  -vf "zscale=t=linear:p=bt709,\
       tonemap=hable,\
       zscale=w=1146:h=480:t=bt709:m=bt709:r=full,format=yuv420p,\
       crop=w=854" \
  -vcodec libx264 \
  -b:v 1250k \
  -pass 2 \
  -preset veryslow \
  -g 1080 \
  -ab 96k \
  -movflags +faststart \
  -y yikes-small-compat.mp4
*/