diff --git a/src/frontend/source.ts b/src/frontend/source.ts
new file mode 100644
index 0000000..e69bcc1
--- /dev/null
+++ b/src/frontend/source.ts
@@ -0,0 +1,198 @@
+import { promises as fs } from 'fs'
+import ora from 'ora'
+import path from 'path'
+
+import { createSubTmp, exists, mount, TempState } from '../util/fs'
+import { ALL_SYS_PARTITIONS } from '../util/partitions'
+import { run } from '../util/process'
+import { isSparseImage } from '../util/sparse'
+import { listZipFiles } from '../util/zip'
+
+async function containsParts(src: string, suffix: string = '') {
+  // If any sys partitions are present
+  for (let part of ALL_SYS_PARTITIONS) {
+    let path = `${src}/${part}${suffix}`
+    try {
+      if (await exists(path)) {
+        return true
+      }
+    } catch {
+      // ENOENT
+    }
+  }
+
+  return false
+}
+
+async function mountImg(
+  img: string,
+  dest: string,
+  mountTmp: TempState,
+  spinner: ora.Ora,
+) {
+  // Convert sparse image to raw
+  if (await isSparseImage(img)) {
+    spinner.text = `converting sparse image: ${img}`
+    let sparseTmp = await createSubTmp(mountTmp.rootTmp!, `sparse_img/${path.dirname(img)}`)
+    let rawImg = `${sparseTmp.dir}/${path.basename(img)}`
+    await run(`simg2img ${img} ${rawImg}`)
+    img = rawImg
+  }
+
+  spinner.text = `mounting: ${img}`
+  await mount(img, dest)
+  mountTmp.mounts.push(dest)
+}
+
+async function mountParts(
+  src: string,
+  mountTmp: TempState,
+  spinner: ora.Ora,
+) {
+  let mountRoot = mountTmp.dir
+
+  for (let part of ALL_SYS_PARTITIONS) {
+    let img = `${src}/${part}.img`
+    if (await exists(img)) {
+      let partPath = `${mountRoot}/${part}`
+      await fs.mkdir(partPath)
+      await mountImg(img, partPath, mountTmp, spinner)
+    }
+  }
+}
+
+async function wrapFileSrc(
+  file: string,
+  tmp: TempState,
+  spinner: ora.Ora,
+): Promise<string | null> {
+  let imagesTmp = await createSubTmp(tmp, `src_images/${file}`)
+
+  // Extract images from OTA payload
+  if (path.basename(file) == 'payload.bin') {
+    spinner.text = `extracting images: ${file}`
+    await run(`cd ${imagesTmp.dir}; payload-dumper-go ${file}`)
+
+    let extractedDir = (await fs.readdir(imagesTmp.dir))[0]
+    let imagesPath = `${imagesTmp.dir}/${extractedDir}`
+    return await searchLeafDir(imagesPath, null, null, tmp, spinner)
+  }
+
+  let files = await listZipFiles(file)
+
+  let imagesEntry = files.find(f => f.includes('/image-') && f.endsWith('.zip'))
+  if (imagesEntry != undefined) {
+    // Factory images
+
+    // Extract nested images zip
+    spinner.text = `extracting nested images: ${file}`
+    let imagesFile = `${imagesTmp.dir}/${imagesEntry}`
+    await run(`unzip -d ${imagesTmp.dir} ${file} ${imagesEntry}`)
+    return await wrapFileSrc(imagesFile, tmp, spinner)
+  } else if (files.find(f => f == 'payload.bin') != undefined) {
+    // OTA package
+
+    // Extract update_engine payload
+    spinner.text = `extracting OTA payload: ${file}`
+    let payloadFile = `${imagesTmp.dir}/payload.bin`
+    await run(`unzip -d ${imagesTmp.dir} ${file} payload.bin`)
+    return await wrapFileSrc(payloadFile, tmp, spinner)
+  } else if (files.find(f => f.endsWith('.img') && ALL_SYS_PARTITIONS.has(f.replace('.img', '')))) {
+    // Images zip
+
+    // Extract image files
+    spinner.text = `extracting images: ${file}`
+    await run(`unzip -d ${imagesTmp.dir} ${file}`)
+    return await searchLeafDir(imagesTmp.dir, null, null, tmp, spinner)
+  } else {
+    throw new Error(`File '${file}' has unknown format`)
+  }
+}
+
+async function searchLeafDir(
+  src: string,
+  device: string | null,
+  buildId: string | null,
+  tmp: TempState,
+  spinner: ora.Ora,
+): Promise<string | null> {
+  if (!(await exists(src))) {
+    return null
+  }
+
+  if (await containsParts(src)) {
+    // Root of mounted images
+    return src
+  } else if (await containsParts(src, '.img')) {
+    // Mount images: <images>.img
+
+    // Mount the images
+    let mountTmp = await createSubTmp(tmp, `sysroot/${src}`)
+    await mountParts(src, mountTmp, spinner)
+    return mountTmp.dir
+  } else if (device != null && buildId != null) {
+    let imagesZip = `${src}/image-${device}-${buildId}.zip`
+    if (await exists(imagesZip)) {
+      // Factory images - nested images package: image-$device-$buildId.zip
+      return await wrapFileSrc(imagesZip, tmp, spinner)
+    }
+
+    let factoryZip = (await fs.readdir(src))
+      .find(f => f.startsWith(`${device}-${buildId}-factory-`))
+    if (factoryZip != undefined) {
+      // Factory images zip
+      return await wrapFileSrc(`${src}/${factoryZip}`, tmp, spinner)
+    }
+  }
+
+  return null
+}
+
+export async function wrapSystemSrc(
+  src: string,
+  device: string,
+  buildId: string | null,
+  tmp: TempState,
+  spinner: ora.Ora,
+) {
+  let stat = await fs.stat(src)
+  if (stat.isDirectory()) {
+    // Directory
+
+    let tryDirs = [
+      src,
+      `${src}/${device}`,
+      ...(buildId != null && [
+        `${src}/${buildId}`,
+        `${src}/${device}/${buildId}`,
+        `${src}/${buildId}/${device}`,
+      ] || []),
+    ]
+
+    // Also try to find extracted factory images: device-buildId
+    if (buildId != null) {
+      tryDirs.push(...tryDirs.map(p => `${p}/${device}-${buildId}`))
+    }
+
+    for (let dir of tryDirs) {
+      let wrapped = await searchLeafDir(dir, device, buildId, tmp, spinner)
+      if (wrapped != null) {
+        spinner.text = wrapped.startsWith(tmp.dir) ? path.relative(tmp.dir, wrapped) : wrapped
+        return wrapped
+      }
+    }
+
+    throw new Error(`No supported source format found in '${src}'`)
+  } else if (stat.isFile()) {
+    // File
+
+    // Attempt to extract factory images or OTA
+    let wrapped = await wrapFileSrc(src, tmp, spinner)
+    if (wrapped != null) {
+      spinner.text = wrapped.startsWith(tmp.dir) ? path.relative(tmp.dir, wrapped) : wrapped
+      return wrapped
+    }
+  }
+
+  throw new Error(`Source '${src}' has unknown type`)
+}