Random preloading?

[petyaracz]

A task has n conditions and a different set of videos for each condition. Since each condition involves a bazillion videos, I only want to preload the videos that are called in the condition that is active for the participant.

I managed to make a version where I preload everything and then pick videos. But this is computationally wasteful.

I wrote a demo version for proof of concept.

Here is the preload-pick-play part of my timeline:

// videos

  var vid_cond1 = [
        {video: ['stimuli/v1.mp4']}
        ];

  var vid_cond2 = [
        {video: ['stimuli/v2.mp4']}
        ];

// build array for preloading

  let filenames = [];

  vid_cond1.forEach((element) => {
    filenames.push(element.video);
  });

  vid_cond2.forEach((element) => {
    filenames.push(element.video);
  });

// preload every video  
  var preload = {
    type: jsPsychPreload,
    videos: filenames
    };

// pick condition
  var stim_list = [vid_cond1,vid_cond2];
  var stimuli_num = jsPsych.randomization.shuffle([0,1])[0];
  var vid_timeline = stim_list[stimuli_num];

// loop through all 1 videos
  var vid_trial = {
    type: jsPsychVideoKeyboardResponse,
    stimulus: jsPsych.timelineVariable('video'),
    width: 250,
    choices: "NO_KEYS",
    autoplay: true,
    controls: false,
    response_allowed_while_playing: false,
    trial_ends_after_video: true,
    response_ends_trial: false
    };

  var vid_trials = {
    timeline_variables: vid_timeline,
    timeline: [vid_trial],
    randomize_order: true
    };

The entire task is here.

[jodeleeuw]

Hi @petyaracz,

Since you've got stimuli_num as the condition and stim_list as a list of all the videos in that condition you could just preload only those videos:

var stim_list = [vid_cond1,vid_cond2];
var stimuli_num = jsPsych.randomization.shuffle([0,1])[0];
var vid_timeline = stim_list[stimuli_num];

var filenames = stim_list[stimuli_num].map((element) => element.video);

var preload = {
    type: jsPsychPreload,
    videos: filenames
 };

[petyaracz]

As a follow-up:

I can loop through a randomly selected array like this:

var a = [
        {video: ['v1.mp4']},
        {video: ['v2.mp4']}
        ];

var b = [
        {video: ['v3.mp4']},
        {video: ['v4.mp4']}
        ];

var condition_num = jsPsych.randomization.shuffle([0,1])[0];
var v = [a,b];

var trial = {
    type: jsPsychVideoKeyboardResponse,
    stimulus: jsPsych.timelineVariable('video')
    };

var trials = {
    timeline_variables: v[condition_num],
    timeline: [training_trial]
    };

I can't do this if I want to pick a single random video and add it as stimulus across different trials:

var targets = [
        {video: ['v1.mp4']},
        {video: ['v2.mp4']}
        ];

var trial = {
    type: jsPsychVideoKeyboardResponse,
    stimulus: targets[condition_num]
    };

Results in jspsych printing [Object] instead of embedding the video. This has to do with how jspsych treats paths for videos in arrays. I've seen something about this somewhere but can't find it.

I could do this but it's super clunky:

var a = [
        {video: ['v1.mp4']},
        ];

var b = [
        {video: ['v2.mp4']},
        ];

var condition_num = jsPsych.randomization.shuffle([0,1])[0];
var v = [a,b];

var trial = {
    type: jsPsychVideoKeyboardResponse,
    stimulus: jsPsych.timelineVariable('video')
    };

var trials = {
    timeline_variables: v[condition_num],
    timeline: [training_trial]
    };

🙏

[petyaracz]

For a timeline, I need to have a format of

array = [
{video: ['a.mp4']},
{video: ['b.mp4']}
]

For an individual trial, I need to have the format

array = [
['a.mp4'],
['b.mp4']
]

So this works:

  var vids = [
        ['stimuli/v1.mp4'],
        ['stimuli/v2.mp4']
        ];

  var stimuli_num = jsPsych.randomization.shuffle([0,1])[0];

  var trial = {
    type: jsPsychVideoKeyboardResponse,
    stimulus: vids[stimuli_num],
    choices: "NO_KEYS",
    };

This also works:

var a = [
        {video: ['v1.mp4']},
        ];

var b = [
        {video: ['v2.mp4']},
        ];

var condition_num = jsPsych.randomization.shuffle([0,1])[0];
var v = [a,b];

var trial = {
    type: jsPsychVideoKeyboardResponse,
    stimulus: jsPsych.timelineVariable('video')
    };

var trials = {
    timeline_variables: v[condition_num],
    timeline: [trial]
    };

😎