How to get the starting frame of a layer in a Video Timeline

I see you posted this a few times bluebeezle​  

I have the same question and have found the best answer from r-bin here:  Is there any way to move the time indicator of timeline to first frame of the layer using Photoshop script?

His function steps through the document timeline frame by frame, checks if the Transform property of the layer is enabled.  If not enabled... then go to next frame... As soon as it becomes enabled, then you know you have the start frame of that layer.  The same thing can be applied backwards to find the end frame of the layer.  Its a great trick!   But unfortunately too slow for my needs. So like you, I'm searching for a better way to extract the timeline start frame of a layer.  If you can get that start frame, then you can just run a "goToTime"  function to put the playhead at this point.  MUCH faster.   but...  I can't seem to extract a layer's start time.

Any ideas out there? 

(To put the playhead at a set point in the timeline.)

function goToTime(seconds, frames, framerate) {

        var ref33 = new ActionReference();

        ref33.putProperty( charIDToTypeID('Prpr'), stringIDToTypeID('time') );

        ref33.putClass( stringIDToTypeID('timeline') );

        var desc69 = new ActionDescriptor();

        desc69.putReference( charIDToTypeID('null'), ref33 );

        var desc70 = new ActionDescriptor();

        desc70.putInteger( stringIDToTypeID('seconds'), Seconds );

        desc70.putInteger( stringIDToTypeID('frame'),Frame );

        desc70.putDouble( stringIDToTypeID('frameRate'), framerate );

        desc69.putObject( charIDToTypeID('T   '), stringIDToTypeID('timecode'), desc70 );

        executeAction( charIDToTypeID('setd'), desc69, DialogModes.NO );

}

Do you want to process just the first layer or all the layers?

For example a script like this one would process all layers in all groups.

try { if(app.documents.length>0){ app.activeDocument.suspendHistory ('Trim Layers', 'TrimLayers();') } }
catch(e) { alert( e + ': on line '  + e.line );}
function TrimLayers() { 
  var orig_ruler_units = app.preferences.rulerUnits; // save user ruler units  
  var orig_display_dialogs = app.displayDialogs; // Save users Displat Doalogs
  app.preferences.rulerUnits = Units.PIXELS; // set the ruler units to PIXELS
  app.displayDialogs = DialogModes.NO; // Set Dialogs off
  var doc  = app.activeDocument; // get current document 
  var saveactiveLayer = doc.activeLayer; // save activeLayer
  doc.selection.deselect(); // make sure ther is no active selection
  try {processArtLayers(doc);} // Process all Layers
  catch(e) { alert( e + ': on line '  + e.line );} // some unexpected error
  doc.selection.deselect(); // make sure ther is no active selection
  try { doc.activeLayer = saveactiveLayer;} // restore activeLayer
  catch(e) { } // may have been deleted
  app.displayDialogs = orig_display_dialogs; // Reset display dialogs 
  app.preferences.rulerUnits = orig_ruler_units; // reset units to original settings
}
///////////////////////////////////////////////////////////////////////////////
// Function: processsArtLayers
// Input: document or layer set
///////////////////////////////////////////////////////////////////////////////
function processArtLayers(obj) {
    for(var i = obj.artLayers.length-1;0<= i; i--) { // for Layers
  try {TrimLayer(obj.artLayers); } // process Art Layer
  catch(e) {} // don't stop on errors
  }
    for(var i=obj.layerSets.length-1;0<=i;i--) { // for Layer sets
  try {processArtLayers(obj.layerSets);} // process Layer Set
  catch(e) {} // don't stop on errors
  }
}
function TrimLayer(layer) { 
  // do nothing if layer is background or locked  
  if(layer.isBackgroundLayer || layer.allLocked || layer.pixelsLocked || layer.positionLocked || layer.transparentPixelsLocked ) return; 
  //if(layer.protectArtboardAutonest ) return;
  if( layer.kind != LayerKind.NORMAL) return; // do nothing if not normal layer   
  app.activeDocument.activeLayer = layer; // target layer
  var bounds = layer.bounds; // layer bounds  
  var LWidth = bounds[2]-bounds[0]; // layer width  
  var LHeight = bounds[3]-bounds[1]; // layer height 
  var Lleft =  bounds[0]; // layer left x
  var Lright =  bounds[2]; // layer right x
  var Ltop =  bounds[1]; // layer top y
  var Lbottom =  bounds[3]; // layer bottom y
  var tlrnc = 20; // tolerance
  i=0.6; // fudge factor
  try {
  MagicWand((Lleft+i), (Ltop+i), tlrnc); // top left
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {}; // do nothing
  try {
  MagicWand((Lleft+LWidth/2), (Ltop+i), tlrnc); // top middle
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {};   // do nothing
  try {
  MagicWand((Lright-i), (Ltop+i), tlrnc); // top right
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {}; // do nothing 
  try {
  MagicWand((Lleft+i), (Ltop+LHeight/2), tlrnc); // middle left
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {}; // do nothing 
  try {
  MagicWand((Lright-i), (Ltop+LHeight/2), tlrnc); // middle right
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {}; // do nothing 
  try {
  MagicWand((Lleft+i), (Lbottom-i), tlrnc); // bottom left
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {};   // do nothing
  try {
  MagicWand((Lleft+LWidth/2), (Lbottom-i), tlrnc); // bottom middle
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {}; // do nothing 
  try {
  MagicWand((Lright-i), (Lbottom-i), tlrnc); // bottom right
  app.activeDocument.selection.clear(); // clear
  }
  catch(e) {};   // do nothing
}
function MagicWand(x,y,tolerance) {
var idsetd = charIDToTypeID( "setd" );
    var desc106 = new ActionDescriptor();
    var idnull = charIDToTypeID( "null" );
        var ref60 = new ActionReference();
        var idChnl = charIDToTypeID( "Chnl" );
        var idfsel = charIDToTypeID( "fsel" );
        ref60.putProperty( idChnl, idfsel );
    desc106.putReference( idnull, ref60 );
    var idT = charIDToTypeID( "T   " );
        var desc107 = new ActionDescriptor();
        var idHrzn = charIDToTypeID( "Hrzn" );
        var idPxl = charIDToTypeID( "#Pxl" );
        desc107.putUnitDouble( idHrzn, idPxl, x );
        var idVrtc = charIDToTypeID( "Vrtc" );
        var idPxl = charIDToTypeID( "#Pxl" );
        desc107.putUnitDouble( idVrtc, idPxl, y );
    var idPnt = charIDToTypeID( "Pnt " );
    desc106.putObject( idT, idPnt, desc107 );
    var idTlrn = charIDToTypeID( "Tlrn" );
    desc106.putInteger( idTlrn, tolerance );
    var idAntA = charIDToTypeID( "AntA" );
    desc106.putBoolean( idAntA, true );
executeAction( idsetd, desc106, DialogModes.NO );
}

To do what you want to do I believe you would need  to flatten your video layer into frame layers and process all the document layer through your action,  Photoshop only supports up to 8,000 layers so you could process videos that are less the 6 minuets in length. I believe you will also loose the Audio.  If you really want to process video you should us video editing applications like Adobe Premier Pro and After Effects.   Photoshop only supports some basic video editing features like trim, splice, transition and can add title and credit  frames.. I think you can also convert a video layer into a smart object layer and use smart filters on the video.