https://github.com/tfausak/rattletrap/issues/49

strip-replay.js

#!/usr/bin/env node
'use strict';

// This is a little JavaScript utility meant to be used with Rattletrap to
// reduce the size of Rocket League replay files. See this issue for more:
// <https://github.com/tfausak/rattletrap/issues/49>. Example usage:
//
//   $ stack exec rattletrap decode < original.replay > original.json
//   $ node strip-replay.js < original.json > stripped.json
//   $ stack exec rattletrap encode < stripped.json > stripped.replay
//
// The resulting stripped replay will usually be about 10% smaller than the
// original one. The exact savings depend on the contents of the replay though.

process.stdin.setEncoding('utf8');

let data = '';
process.stdin.on('data', function (chunk) {
  data += chunk;
});

function isEqual (x, y) {
  if (x === y) {
    return true;
  }

  if (x instanceof Object && y instanceof Object) {
    const keys = Object.keys(x).sort();
    for (const key of keys) {
      if (!isEqual(x[key], y[key])) {
        return false;
      }
    }
    return true;
  }

  return false;
}

process.stdin.on('end', function () {
  const replay = JSON.parse(data);

  replay.header.properties.keys = [];
  replay.header.properties.value = {};

  replay.content.key_frames = [];
  replay.content.marks = [];
  replay.content.messages = [];
  replay.content.stream_size = 0;

  const state = {};

  for (const frame of replay.content.frames) {
    const newReplications = [];

    for (let index = 0; index < frame.replications.length; index += 1) {
      const replication = frame.replications[index];
      const actorId = replication.actor_id.value;

      if (replication.value.hasOwnProperty('spawned_replication_value')) {
        // spawned
        if (!state.hasOwnProperty(actorId)) {
          state[actorId] = {};
          newReplications.push(replication);
        }
      } else if (replication.value.hasOwnProperty('updated_replication_value')) {
        // updated
        const newAttributes = [];

        for (const attribute of replication.value.updated_replication_value) {
          if (!isEqual(state[actorId][attribute.name], attribute.value)) {
            state[actorId][attribute.name] = attribute.value;
            newAttributes.push(attribute);
          }
        }

        if (newAttributes.length > 0) {
          replication.value.updated_replication_value = newAttributes;
          newReplications.push(replication);
        }
      } else {
        // destroyed
        if (state.hasOwnProperty(actorId)) {
          newReplications.push(replication);
          delete state[actorId];
        }
      }
    }

    frame.replications = newReplications;
  }

  console.log(JSON.stringify(replay));
});