converts after effects layers' keyframes to JSON and saves file on hard drive.

convert.jsx

//JSON object
"object"!=typeof JSON&&(JSON={}),function(){"use strict";function f(t){return 10>t?"0"+t:t}function this_value(){return this.valueOf()}function quote(t){return rx_escapable.lastIndex=0,rx_escapable.test(t)?'"'+t.replace(rx_escapable,function(t){var e=meta[t];return"string"==typeof e?e:"\\u"+("0000"+t.charCodeAt(0).toString(16)).slice(-4)})+'"':'"'+t+'"'}function str(t,e){var r,n,o,u,f,a=gap,i=e[t];switch(i&&"object"==typeof i&&"function"==typeof i.toJSON&&(i=i.toJSON(t)),"function"==typeof rep&&(i=rep.call(e,t,i)),typeof i){case"string":return quote(i);case"number":return isFinite(i)?i+"":"null";case"boolean":case"null":return i+"";case"object":if(!i)return"null";if(gap+=indent,f=[],"[object Array]"===Object.prototype.toString.apply(i)){for(u=i.length,r=0;u>r;r+=1)f[r]=str(r,i)||"null";return o=0===f.length?"[]":gap?"[\n"+gap+f.join(",\n"+gap)+"\n"+a+"]":"["+f.join(",")+"]",gap=a,o}if(rep&&"object"==typeof rep)for(u=rep.length,r=0;u>r;r+=1)"string"==typeof rep[r]&&(n=rep[r],o=str(n,i),o&&f.push(quote(n)+(gap?": ":":")+o));else for(n in i)Object.prototype.hasOwnProperty.call(i,n)&&(o=str(n,i),o&&f.push(quote(n)+(gap?": ":":")+o));return o=0===f.length?"{}":gap?"{\n"+gap+f.join(",\n"+gap)+"\n"+a+"}":"{"+f.join(",")+"}",gap=a,o}}var rx_one=/^[\],:{}\s]*$/,rx_two=/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g,rx_three=/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g,rx_four=/(?:^|:|,)(?:\s*\[)+/g,rx_escapable=/[\\\"\u0000-\u001f\u007f-\u009f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,rx_dangerous=/[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g;"function"!=typeof Date.prototype.toJSON&&(Date.prototype.toJSON=function(){return isFinite(this.valueOf())?this.getUTCFullYear()+"-"+f(this.getUTCMonth()+1)+"-"+f(this.getUTCDate())+"T"+f(this.getUTCHours())+":"+f(this.getUTCMinutes())+":"+f(this.getUTCSeconds())+"Z":null},Boolean.prototype.toJSON=this_value,Number.prototype.toJSON=this_value,String.prototype.toJSON=this_value);var gap,indent,meta,rep;"function"!=typeof JSON.stringify&&(meta={"\b":"\\b","	":"\\t","\n":"\\n","\f":"\\f","\r":"\\r",'"':'\\"',"\\":"\\\\"},JSON.stringify=function(t,e,r){var n;if(gap="",indent="","number"==typeof r)for(n=0;r>n;n+=1)indent+=" ";else"string"==typeof r&&(indent=r);if(rep=e,e&&"function"!=typeof e&&("object"!=typeof e||"number"!=typeof e.length))throw Error("JSON.stringify");return str("",{"":t})}),"function"!=typeof JSON.parse&&(JSON.parse=function(text,reviver){function walk(t,e){var r,n,o=t[e];if(o&&"object"==typeof o)for(r in o)Object.prototype.hasOwnProperty.call(o,r)&&(n=walk(o,r),void 0!==n?o[r]=n:delete o[r]);return reviver.call(t,e,o)}var j;if(text+="",rx_dangerous.lastIndex=0,rx_dangerous.test(text)&&(text=text.replace(rx_dangerous,function(t){return"\\u"+("0000"+t.charCodeAt(0).toString(16)).slice(-4)})),rx_one.test(text.replace(rx_two,"@").replace(rx_three,"]").replace(rx_four,"")))return j=eval("("+text+")"),"function"==typeof reviver?walk({"":j},""):j;throw new SyntaxError("JSON.parse")})}();

//log wrapper
function log( arg ){$.writeln( arg );}

//gets a URL based on the file path and the name 
function getUrl( name ){
    var projectName = app.project.file.name.replace(".aep", '');
    var compName = app.project.activeItem.name;
    var fileName    = name || projectName + "_"+ compName + ".json";
    fileName    = fileName.replace(/\s/g, '');
    var path = app.project.file.parent.absoluteURI + "/";
    return path + fileName;
}

//   you need to allow AE to write files to your hard drive:
//   go to: Edit > Preferences > General > and check on "Allow Scripts to Write Files and Access Network"
//
//write the output to disk:
function saveFile( obj, fileName ){
    var output = new File( getUrl(  fileName + ".json" ) );
    if( output.open( "w" ) ){
        output.encoding = "UTF-8";
        var content =JSON.stringify( out, undefined, 2 );
        output.write( content );
        output.close();
    }

}

//recursive method to get all values from all layers
function scanLayers( obj, id, props ){

    if( id > comp.layers.length )return;
    
    //for each layer 
    var layer = comp.layer(id);
    if( layer == null ) return;
    
    //stores all layer's values in an object
    var tmp = {};
    tmp.times = [];

    //for each property  passed as an argument
    for( var p =0; p< props.length; p++ ){

        var property = layer[ props[ p ] ]; 
        
        //gets the keyframe count
        var numKeys = property.numKeys; 
        
        //default value if property is not animated
        if( numKeys <= 0 ){
            tmp[ props[ p ] ] = null;
            continue;
        }
    
        //if the property is animated 
        var values = [];
        if (numKeys > 0){ 
        
        
            var time, value; 
            for( var i = 1; i <= numKeys; i++ ){

                //gets the time and property values at this keyFrame
                time = property.keyTime( i ); 
                value = property.keyValue( i );
                
                //stores them into an array which first value is the time stamp
                var keyframe = [time];
                if( !isNaN( value ) ){
                    // stores rotations in RADIANS
                    if( props[ p ] == "rotation" ) 
                    {
                        keyframe.push( value * Math.PI / 180 );
                    }
                    else
                    {
                        keyframe.push( value );
                    }
                }
                else
                {
                    for( var j = 0; j < value.length; j++ ){
                        keyframe.push( value[ j ] );
                    }
                }                
                //store this keyframe in the layer object
                values.push( keyframe );
                
                //if this timestamp was not yet present in the layer's list of timestamps
                var addTime = true;
                for( var j = 0; j < tmp.times.length; j++ ){
                    if( tmp.times[ j ] == time ) addTime = false;
                }
                //add it
                if( addTime ) tmp.times.push( time );
            }
        }
        //stores the property's values for this layer and got ot next property
        tmp[ props[ p ] ] = values;
        
      }
  
      // add this layer to the final object
      obj[ layer.name.replace(/\s/g, '_' ).toLowerCase() ] = tmp; 
      return scanLayers (obj, ++id, props);

}

////////////////////////////////////////////////

// SETUP WINDOW 

////////////////////////////////////////////////


var win = new Window('dialog', 'Alert Box Builder'); 
win.options = win.add('panel', undefined, 'Build it'); 

var prs = [
    "position", 
    "rotation",
    "scale"
    ];
    
for( var i = 0; i < prs.length; i++ )
{
    win[ prs[ i ] ] = win.options.add('checkbox', undefined,   prs[ i ] ); 
    win[ prs[ i ] ].value = true;
}

win.options.fileNameLabel = win.options.add('statictext', undefined, 'json file name:'); 
win.options.fileName = win.options.add('edittext', undefined, 'fileName' );
win.options.buildBtn = win.options.add('button', undefined, 'Build',  {name:'ok'}); 
win.show(); 


//specify properties to export
var properties = [];
for( var i = 0; i < prs.length; i++ ){
    
    log( prs[i] + " -> " + win[ prs[ i ] ].value );
    if( win[ prs[ i ] ].value ) properties.push( prs[ i ] );
    
}

//specify file name or fall back to file name + .json
var fileName = win.options.fileName.text;
if( fileName == "fileName" ) fileName = app.project.file.name.replace(".aep", '');


////////////////////////////////////////////////

// GO !

////////////////////////////////////////////////

var proj = app.project; 
var comp = proj.activeItem; 
var out = {};
saveFile( scanLayers( out, 1,  properties ), fileName );

sample.json

{
  "bla": {
    "times": [
      0,
      38.0046713380047,
      50.6172839506173,
      37.7711044377711
    ],
    "position": [
      [
        0,
        430,
        450,
        0
      ],
      [
        38.0046713380047,
        474,
        96,
        0
      ],
      [
        50.6172839506173,
        394,
        156,
        0
      ]
    ],
    "rotation": null,
    "scale": [
      [
        0,
        100,
        100,
        100
      ],
      [
        37.7711044377711,
        100,
        -14122.2222222222,
        100
      ],
      [
        38.0046713380047,
        100,
        99.9999999999982,
        100
      ]
    ]
  },
  "red_solid_1": {
    "times": [
      38.0046713380047,
      43.1431431431431,
      46.6466466466466
    ],
    "position": null,
    "rotation": null,
    "scale": [
      [
        38.0046713380047,
        100,
        100,
        100
      ],
      [
        43.1431431431431,
        244,
        244,
        100
      ],
      [
        46.6466466466466,
        100,
        100,
        100
      ]
    ]
  },
  "rect": {
    "times": [
      40.5739072405739,
      54.5879212545879,
      38.0046713380047,
      50.6172839506173,
      59.693026359693
    ],
    "position": null,
    "rotation": [
      [
        40.5739072405739,
        1.81828270071446
      ],
      [
        54.5879212545879,
        0
      ]
    ],
    "scale": [
      [
        38.0046713380047,
        8.203125,
        7.8125,
        100
      ],
      [
        40.5739072405739,
        26.0121527777778,
        27.3032407407407,
        100
      ],
      [
        50.6172839506173,
        76.453125,
        72.8125,
        100
      ],
      [
        59.693026359693,
        8.203125,
        7.8125,
        100
      ]
    ]
  }
}

How does it handle it if the keyframes for different properties are at different times? Eg, scale settings every second, but position settings every two seconds? I'm guessing it has a time entry for every key frame, and if the property doesn't have a specific value at that time, it interpolates it?

EDIT: My apologies, I misread the code. Looks like it embeds the time stamp at the start of each one. :) Great stuff.