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 );
$options = [
    'letterbox' => false,
    'audio' => false,
];

while ( count( $args ) > 0 && substr( $args[0], 0, 2 ) == '--' ) {
    $option = substr( array_shift( $args ), 2 );
    $options[$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"
    );
}
[ $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 convert( $src, $dest, $options ) {
    $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 );


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

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

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

    $filters = [ "scale=w=$scaleWidth:h=$scaleHeight" ];
    if ( $hdr ) {
        $filters[] = "zscale=t=linear:p=bt709";
        $filters[] = "tonemap=hable:peak=8";
        $filters[] = "zscale=t=bt709:m=bt709:r=full";
    }
    $filters[] = "format=yuv420p";
    if ( $options['letterbox'] ) {
        $offset = round( ( $frameHeight - $scaleHeight) / 2 );
        $filters[] = "pad=h=$frameHeight:y=$offset";
    } else {
        $filters[] = "crop=w=$frameWidth";
    }
    $vf = implode( ',', $filters );

    $fps = 30;

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