pack-vid/pack-vid

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

// Squishes given video input into sub-4000kb .mp4
// Crops or pads to 16:9 (crop default; --letterbox to pad)
// Strips audio (to override, pass --audio for 96 kbps AAC)
// 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 );

$maxBytes = 4000 * 1000; // fit in 4MB
$maxBytes = $maxBytes * 7 / 8; // leave some headroom

$options = [
    'letterbox' => false,
    'audio' => false,
    'exposure' => '0',
    'peak' => '10000',
    'fps' => '60',
    'size' => $maxBytes,
];

while ( count( $args ) > 0 && substr( $args[0], 0, 2 ) == '--' ) {
    $option = substr( array_shift( $args ), 2 );
    $parts = explode( '=', $option, 2 );
    if ( count( $parts ) == 2 ) {
        [ $key, $val ] = $parts;
        $options[$key] = $val;
    } else {
        $options[$option] = true;
    }
}

if ( count ( $args ) < 2 ) {
    die(
        "Usage: $self [options...] <srcfile.mp4> <destfile.mp4>\n" .
        "Options:\n" .
        "  --letterbox    pad instead of cropping\n" .
        "  --audio        include audio\n" .
        "  --exposure=n   adjust exposure\n" .
        "  --peak=n       set HDR peak nits\n" .
        "  --fps=n        frame rate limit\n" .
        "  --size=n       target file size in bytes (default 3.5M)\n"
    );
}
[ $src, $dest ] = $args;
convert( $src, $dest, $options );
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 sizify( $str ) {
    $matches = [];
    if ( preg_match( '/^(\d+(?:\.\d+)?)([kmgt]?)$/i', $str, $matches ) ) {
        [ , $digits, $suffix ] = $matches;
        $n = floatval( $digits );
        switch ( strtolower( $suffix ) ) {
            case 't': $n *= 1000; // fall through
            case 'g': $n *= 1000; // fall through
            case 'm': $n *= 1000; // fall through
            case 'k': $n *= 1000; // fall through
            default: return $n;
        }
        return $n;
    }
    die( "Unexpected size format '$str'\n" );
}

function convert( $src, $dest, $options ) {
    $maxBits = 8 * sizify( $options['size'] );

    $probe = ffprobe( $src );

    $videoTracks = array_values(
        array_filter( $probe->streams, function ( $stream ) {
            return $stream->codec_type === 'video';
        } )
    );
    if ( count( $videoTracks ) == 0 ) {
        var_dump( $probe );
        die("oh no\n");
    }
    $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 );


    if ( $options[ 'audio' ] ) {
        $audioBitrate = 96 * 1000;
        $audio = [ '-b:a', $audioBitrate ];
        $bitrate -= $audioBitrate;
    } else {
        $audio = [ '-an' ];
    }

    $mbits = 1000 * 1000;
    if ( $bitrate < $mbits || $height < 480 ) {
        $frameWidth = 640;
        $frameHeight = 360;
    } elseif ( $bitrate < 2 * $mbits || $height < 720) {
        $frameWidth = 854;
        $frameHeight = 480;
    } elseif ( $bitrate < 4 * $mbits || $height < 1080) {
        $frameWidth = 1280;
        $frameHeight = 720;
    } else {
        $frameWidth = 1920;
        $frameHeight = 1080;
    }

    $aspect = $width / $height;
    $wide = $aspect > ( $frameWidth / $frameHeight );
    $pad = boolval( $options['letterbox'] );
    if ( $pad ) {
        if ( $wide ) {
            $scaleWidth = $frameWidth;
            $scaleHeight = evenize( $frameWidth / $aspect );
        } else {
            $scaleHeight = $frameHeight;
            $scaleWidth = evenize( $frameHeight * $aspect );
        }
    } else {
        if ( $wide ) {
            $scaleHeight = $frameHeight;
            $scaleWidth = evenize( $frameHeight * $aspect );
        } else {
            $scaleWidth = $frameWidth;
            $scaleHeight = evenize( $frameWidth / $aspect );
        }
    }

    $exposure = floatval( $options['exposure'] );
    $peakNits = floatval( $options['peakNits'] );
    $sdrNits = 80;
    $peak = $peakNits / $sdrNits;

    $filters = [ "scale=w=$scaleWidth:h=$scaleHeight" ];
    if ( $hdr ) {
        $filters[] = "zscale=t=linear:p=bt709";
        if ( $exposure ) {
            $filters[] = "exposure=$exposure";
        }
        $filters[] = "tonemap=hable:peak=$peak";
        $filters[] = "zscale=t=bt709:m=bt709:r=full";
    }
    $filters[] = "format=yuv420p";
    if ( $options['letterbox'] ) {
        $offsetX = round( ( $frameWidth - $scaleWidth) / 2 );
        $offsetY = round( ( $frameHeight - $scaleHeight) / 2 );
        $filters[] = "pad=w=$frameWidth:h=$frameHeight:x=$offsetX:y=$offsetY";
    } else {
        $filters[] = "crop=w=$frameWidth:h=$frameHeight";
    }
    $vf = implode( ',', $filters );

    $fps = $options['fps'];

    // $preset = 'veryslow'; // annoying at higher resolutions
    $preset = 'slow';

    $passlog = tempnam( '.', 'pack-vid-passlog' );
    run( 'ffmpeg',
        array_merge( [
            '-i', $src,
            '-f', 'mp4',
            '-fpsmax', $fps,
            '-vf', $vf,
            '-c:v', 'libx264',
            '-b:v', $bitrate,
            '-preset', $preset,
            '-pass', '1',
            '-passlogfile', $passlog,
            '-g', $keyframeInt,
        ], $audio, [
            '-y', '/dev/null'
        ] )
    );
    run( 'ffmpeg',
        array_merge( [
            '-i', $src,
            '-vf', $vf,
            '-fpsmax', $fps,
            '-c:v', 'libx264',
            '-b:v', $bitrate,
            '-preset', $preset,
            '-pass', '2',
            '-passlogfile', $passlog,
            '-g', $keyframeInt,
        ], $audio, [
            '-movflags', '+faststart',
            '-y', $dest
        ] )
    );
}