diff --git a/selfdrive/camerad/SConscript b/selfdrive/camerad/SConscript
index 65be54aa4e..d018704d60 100644
--- a/selfdrive/camerad/SConscript
+++ b/selfdrive/camerad/SConscript
@@ -21,8 +21,12 @@ else:
     if USE_FRAME_STREAM:
       cameras = ['cameras/camera_frame_stream.cc']
     else:
-      libs += ['avutil', 'avcodec', 'avformat', 'swscale']
-      cameras = ['cameras/camera_replay.cc', env.Object('camera-framereader', '#/selfdrive/ui/replay/framereader.cc')]
+      libs += ['avutil', 'avcodec', 'avformat', 'swscale', 'bz2', 'ssl', 'curl', 'crypto']
+      # TODO: import replay_lib from root SConstruct
+      cameras = ['cameras/camera_replay.cc', 
+        env.Object('camera-util', '#/selfdrive/ui/replay/util.cc'),
+        env.Object('camera-framereader', '#/selfdrive/ui/replay/framereader.cc'),
+        env.Object('camera-filereader', '#/selfdrive/ui/replay/filereader.cc')]
 
   if arch == "Darwin":
     del libs[libs.index('OpenCL')]
diff --git a/selfdrive/camerad/cameras/camera_replay.cc b/selfdrive/camerad/cameras/camera_replay.cc
index 0345f37b74..6bc53d8c94 100644
--- a/selfdrive/camerad/cameras/camera_replay.cc
+++ b/selfdrive/camerad/cameras/camera_replay.cc
@@ -23,8 +23,7 @@ std::string get_url(std::string route_name, const std::string &camera, int segme
 }
 
 void camera_init(VisionIpcServer *v, CameraState *s, int camera_id, unsigned int fps, cl_device_id device_id, cl_context ctx, VisionStreamType rgb_type, VisionStreamType yuv_type, const std::string &url) {
-  // TODO: cache url file
-  s->frame = new FrameReader();
+  s->frame = new FrameReader(true);
   if (!s->frame->load(url)) {
     printf("failed to load stream from %s", url.c_str());
     assert(0);
diff --git a/selfdrive/loggerd/SConscript b/selfdrive/loggerd/SConscript
index dfa3dca714..7e41c9d3ee 100644
--- a/selfdrive/loggerd/SConscript
+++ b/selfdrive/loggerd/SConscript
@@ -28,4 +28,4 @@ env.Program(src, LIBS=libs)
 env.Program('bootlog.cc', LIBS=libs)
 
 if GetOption('test'):
-  env.Program('tests/test_logger', ['tests/test_runner.cc', 'tests/test_logger.cc', env.Object('logger_util', '#/selfdrive/ui/replay/util.cc')], LIBS=[libs] + ['curl'])
+  env.Program('tests/test_logger', ['tests/test_runner.cc', 'tests/test_logger.cc', env.Object('logger_util', '#/selfdrive/ui/replay/util.cc')], LIBS=[libs] + ['curl', 'crypto'])
diff --git a/selfdrive/loggerd/tests/test_logger.cc b/selfdrive/loggerd/tests/test_logger.cc
index e59c2f0153..baef312ad8 100644
--- a/selfdrive/loggerd/tests/test_logger.cc
+++ b/selfdrive/loggerd/tests/test_logger.cc
@@ -21,12 +21,8 @@ void verify_segment(const std::string &route_path, int segment, int max_segment,
   REQUIRE(!util::file_exists(segment_path + "/rlog.bz2.lock"));
   for (const char *fn : {"/rlog.bz2", "/qlog.bz2"}) {
     const std::string log_file = segment_path + fn;
-    INFO(log_file);
-    
-    std::ostringstream stream;
-    bool ret = readBZ2File(log_file, stream);
-    REQUIRE(ret);
-    std::string log = stream.str();
+    std::string log = decompressBZ2(util::read_file(log_file));
+    REQUIRE(!log.empty());
     int event_cnt = 0, i = 0;
     kj::ArrayPtr<const capnp::word> words((capnp::word *)log.data(), log.size() / sizeof(capnp::word));
     while (words.size() > 0) {
diff --git a/selfdrive/ui/SConscript b/selfdrive/ui/SConscript
index 4d3ae49ba0..17441b6ba6 100644
--- a/selfdrive/ui/SConscript
+++ b/selfdrive/ui/SConscript
@@ -112,7 +112,7 @@ if GetOption('extras'):
 if arch in ['x86_64', 'Darwin'] or GetOption('extras'):
   qt_env['CXXFLAGS'] += ["-Wno-deprecated-declarations"]
 
-  replay_lib_src = ["replay/replay.cc", "replay/camera.cc", "replay/logreader.cc", "replay/framereader.cc", "replay/route.cc", "replay/util.cc"]
+  replay_lib_src = ["replay/replay.cc", "replay/camera.cc", "replay/filereader.cc", "replay/logreader.cc", "replay/framereader.cc", "replay/route.cc", "replay/util.cc"]
 
   replay_lib = qt_env.Library("qt_replay", replay_lib_src, LIBS=base_libs)
   replay_libs = [replay_lib, 'avutil', 'avcodec', 'avformat', 'bz2', 'curl', 'swscale'] + qt_libs
diff --git a/selfdrive/ui/replay/filereader.cc b/selfdrive/ui/replay/filereader.cc
new file mode 100644
index 0000000000..1585631401
--- /dev/null
+++ b/selfdrive/ui/replay/filereader.cc
@@ -0,0 +1,62 @@
+#include "selfdrive/ui/replay/filereader.h"
+
+#include <sys/stat.h>
+
+#include <cassert>
+#include <cmath>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+
+#include "selfdrive/common/util.h"
+#include "selfdrive/ui/replay/util.h"
+
+std::string cacheFilePath(const std::string &url) {
+  static std::string cache_path = [] {
+    const std::string comma_cache = util::getenv("COMMA_CACHE", "/tmp/comma_download_cache/");
+    util::create_directories(comma_cache, 0755);
+    return comma_cache.back() == '/' ? comma_cache : comma_cache + "/";
+  }();
+
+  return cache_path + sha256(getUrlWithoutQuery(url));;
+}
+
+std::string FileReader::read(const std::string &file, std::atomic<bool> *abort) {
+  const bool is_remote = file.find("https://") == 0;
+  const std::string local_file = is_remote ? cacheFilePath(file) : file;
+  std::string result;
+
+  if ((!is_remote || cache_to_local_) && util::file_exists(local_file)) {
+    result = util::read_file(local_file);
+  } else if (is_remote) {
+    result = download(file, abort);
+    if (cache_to_local_ && !result.empty()) {
+      std::ofstream fs(local_file, fs.binary | fs.out);
+      fs.write(result.data(), result.size());
+    }
+  }
+  return result;
+}
+
+std::string FileReader::download(const std::string &url, std::atomic<bool> *abort) {
+  std::string result;
+  size_t remote_file_size = 0;
+  for (int i = 0; i <= max_retries_ && !(abort && *abort); ++i) {
+    if (i > 0) {
+      std::cout << "download failed, retrying" << i << std::endl;
+    }
+    if (remote_file_size <= 0) {
+      remote_file_size = getRemoteFileSize(url);
+    }
+    if (remote_file_size > 0 && !(abort && *abort)) {
+      std::ostringstream oss;
+      result.resize(remote_file_size);
+      oss.rdbuf()->pubsetbuf(result.data(), result.size());
+      int chunks = chunk_size_ > 0 ? std::min(1, (int)std::nearbyint(remote_file_size / (float)chunk_size_)) : 1;
+      if (httpMultiPartDownload(url, oss, chunks, remote_file_size, abort)) {
+        return result;
+      }
+    }
+  }
+  return {};
+}
diff --git a/selfdrive/ui/replay/filereader.h b/selfdrive/ui/replay/filereader.h
new file mode 100644
index 0000000000..06ce14e9f2
--- /dev/null
+++ b/selfdrive/ui/replay/filereader.h
@@ -0,0 +1,20 @@
+#pragma once
+
+#include <atomic>
+#include <string>
+
+class FileReader {
+public:
+  FileReader(bool cache_to_local, int chunk_size = -1, int max_retries = 3)
+      : cache_to_local_(cache_to_local), chunk_size_(chunk_size), max_retries_(max_retries) {}
+  virtual ~FileReader() {}
+  std::string read(const std::string &file, std::atomic<bool> *abort = nullptr);
+
+private:
+  std::string download(const std::string &url, std::atomic<bool> *abort);
+  int chunk_size_;
+  int max_retries_;
+  bool cache_to_local_;
+};
+
+std::string cacheFilePath(const std::string &url);
diff --git a/selfdrive/ui/replay/framereader.cc b/selfdrive/ui/replay/framereader.cc
index dd29d6363f..b6092a0df9 100644
--- a/selfdrive/ui/replay/framereader.cc
+++ b/selfdrive/ui/replay/framereader.cc
@@ -3,8 +3,11 @@
 #include <unistd.h>
 #include <cassert>
 #include <mutex>
+#include <sstream>
 
-static int ffmpeg_lockmgr_cb(void **arg, enum AVLockOp op) {
+namespace {
+
+int ffmpeg_lockmgr_cb(void **arg, enum AVLockOp op) {
   std::mutex *mutex = (std::mutex *)*arg;
   switch (op) {
   case AV_LOCK_CREATE:
@@ -22,38 +25,56 @@ static int ffmpeg_lockmgr_cb(void **arg, enum AVLockOp op) {
   return 0;
 }
 
-struct AVInitializer {
-  AVInitializer() {
-    int ret = av_lockmgr_register(ffmpeg_lockmgr_cb);
-    assert(ret >= 0);
+int readFunction(void *opaque, uint8_t *buf, int buf_size) {
+  auto &iss = *reinterpret_cast<std::istringstream *>(opaque);
+  iss.read(reinterpret_cast<char *>(buf), buf_size);
+  return iss.gcount() ? iss.gcount() : AVERROR_EOF;
+}
+
+} // namespace
+
+FrameReader::FrameReader(bool local_cache, int chunk_size, int retries) : FileReader(local_cache, chunk_size, retries) {
+  static std::once_flag once_flag;
+  std::call_once(once_flag, [] {
+    av_lockmgr_register(ffmpeg_lockmgr_cb);
     av_register_all();
-    avformat_network_init();
-  }
-  ~AVInitializer() { avformat_network_deinit(); }
-};
+  });
+
+  pFormatCtx_ = avformat_alloc_context();
+  av_frame_ = av_frame_alloc();
+  rgb_frame_ = av_frame_alloc();
+  yuv_frame_ = av_frame_alloc();;
 
-FrameReader::FrameReader() {
-  static AVInitializer av_initializer;
 }
 
 FrameReader::~FrameReader() {
   for (auto &f : frames_) {
     av_free_packet(&f.pkt);
   }
-  if (pCodecCtx_) {
-    avcodec_close(pCodecCtx_);
-    avcodec_free_context(&pCodecCtx_);
-  }
+  if (pCodecCtx_) avcodec_free_context(&pCodecCtx_);
   if (pFormatCtx_) avformat_close_input(&pFormatCtx_);
   if (av_frame_) av_frame_free(&av_frame_);
   if (rgb_frame_) av_frame_free(&rgb_frame_);
   if (yuv_frame_) av_frame_free(&yuv_frame_);
   if (rgb_sws_ctx_) sws_freeContext(rgb_sws_ctx_);
   if (yuv_sws_ctx_) sws_freeContext(yuv_sws_ctx_);
+
+  if (avio_ctx_) {
+    av_freep(&avio_ctx_->buffer);
+    av_freep(&avio_ctx_);
+  }
 }
 
-bool FrameReader::load(const std::string &url) {
-  pFormatCtx_ = avformat_alloc_context();
+bool FrameReader::load(const std::string &url, std::atomic<bool> *abort) {
+  std::string content = read(url, abort);
+  if (content.empty()) return false;
+
+  std::istringstream iss(content);
+  const int avio_ctx_buffer_size = 64 * 1024;
+  unsigned char *avio_ctx_buffer = (unsigned char *)av_malloc(avio_ctx_buffer_size);
+  avio_ctx_ = avio_alloc_context(avio_ctx_buffer, avio_ctx_buffer_size, 0, &iss, readFunction, nullptr, nullptr);
+  pFormatCtx_->pb = avio_ctx_;
+
   pFormatCtx_->probesize = 10 * 1024 * 1024;  // 10MB
   if (avformat_open_input(&pFormatCtx_, url.c_str(), NULL, NULL) != 0) {
     printf("error loading %s\n", url.c_str());
@@ -75,10 +96,6 @@ bool FrameReader::load(const std::string &url) {
   ret = avcodec_open2(pCodecCtx_, pCodec, NULL);
   if (ret < 0) return false;
 
-  av_frame_ = av_frame_alloc();
-  rgb_frame_ = av_frame_alloc();
-  yuv_frame_ = av_frame_alloc();;
-
   width = (pCodecCtxOrig->width + 3) & ~3;
   height = pCodecCtxOrig->height;
   rgb_sws_ctx_ = sws_getContext(pCodecCtxOrig->width, pCodecCtxOrig->height, AV_PIX_FMT_YUV420P,
@@ -92,7 +109,7 @@ bool FrameReader::load(const std::string &url) {
   if (!yuv_sws_ctx_) return false;
 
   frames_.reserve(60 * 20);  // 20fps, one minute
-  while (true) {
+  while (!(abort && *abort)) {
     Frame &frame = frames_.emplace_back();
     int err = av_read_frame(pFormatCtx_, &frame.pkt);
     if (err < 0) {
diff --git a/selfdrive/ui/replay/framereader.h b/selfdrive/ui/replay/framereader.h
index b05336c0eb..2d42e135fe 100644
--- a/selfdrive/ui/replay/framereader.h
+++ b/selfdrive/ui/replay/framereader.h
@@ -2,6 +2,7 @@
 
 #include <string>
 #include <vector>
+#include "selfdrive/ui/replay/filereader.h"
 
 extern "C" {
 #include <libavcodec/avcodec.h>
@@ -10,11 +11,11 @@ extern "C" {
 #include <libavutil/imgutils.h>
 }
 
-class FrameReader {
+class FrameReader : protected FileReader {
 public:
-  FrameReader();
+  FrameReader(bool local_cache = false, int chunk_size = -1, int retries = 0);
   ~FrameReader();
-  bool load(const std::string &url);
+  bool load(const std::string &url, std::atomic<bool> *abort = nullptr);
   bool get(int idx, uint8_t *rgb, uint8_t *yuv);
   int getRGBSize() const { return width * height * 3; }
   int getYUVSize() const { return width * height * 3 / 2; }
@@ -39,4 +40,5 @@ private:
   AVCodecContext *pCodecCtx_ = nullptr;
   int key_frames_count_ = 0;
   bool valid_ = false;
+  AVIOContext *avio_ctx_ = nullptr;
 };
diff --git a/selfdrive/ui/replay/logreader.cc b/selfdrive/ui/replay/logreader.cc
index 04c42bc1a4..10be8a19c7 100644
--- a/selfdrive/ui/replay/logreader.cc
+++ b/selfdrive/ui/replay/logreader.cc
@@ -1,7 +1,6 @@
 #include "selfdrive/ui/replay/logreader.h"
 
-#include <sstream>
-#include "selfdrive/common/util.h"
+#include <algorithm>
 #include "selfdrive/ui/replay/util.h"
 
 Event::Event(const kj::ArrayPtr<const capnp::word> &amsg, bool frame) : reader(amsg), frame(frame) {
@@ -27,7 +26,7 @@ Event::Event(const kj::ArrayPtr<const capnp::word> &amsg, bool frame) : reader(a
 
 // class LogReader
 
-LogReader::LogReader(size_t memory_pool_block_size) {
+LogReader::LogReader(bool local_cache, int chunk_size, int retries, size_t memory_pool_block_size) : FileReader(local_cache, chunk_size, retries) {
 #ifdef HAS_MEMORY_RESOURCE
   const size_t buf_size = sizeof(Event) * memory_pool_block_size;
   pool_buffer_ = ::operator new(buf_size);
@@ -47,18 +46,9 @@ LogReader::~LogReader() {
 #endif
 }
 
-bool LogReader::load(const std::string &file) {
-  bool is_bz2 = file.rfind(".bz2") == file.length() - 4;
-  if (is_bz2) {
-    std::ostringstream stream;
-    if (!readBZ2File(file, stream)) {
-      LOGW("bz2 decompress failed");
-      return false;
-    }
-    raw_ = stream.str();
-  } else {
-    raw_ = util::read_file(file);
-  }
+bool LogReader::load(const std::string &file, std::atomic<bool> *abort) {
+  raw_ = decompressBZ2(read(file, abort));
+  if (raw_.empty()) return false;
 
   kj::ArrayPtr<const capnp::word> words((const capnp::word *)raw_.data(), raw_.size() / sizeof(capnp::word));
   while (words.size() > 0) {
diff --git a/selfdrive/ui/replay/logreader.h b/selfdrive/ui/replay/logreader.h
index 0fb3711325..5bb613d9de 100644
--- a/selfdrive/ui/replay/logreader.h
+++ b/selfdrive/ui/replay/logreader.h
@@ -7,6 +7,7 @@
 
 #include "cereal/gen/cpp/log.capnp.h"
 #include "selfdrive/camerad/cameras/camera_common.h"
+#include "selfdrive/ui/replay/filereader.h"
 
 const CameraType ALL_CAMERAS[] = {RoadCam, DriverCam, WideRoadCam};
 const int MAX_CAMERAS = std::size(ALL_CAMERAS);
@@ -45,11 +46,11 @@ public:
   bool frame;
 };
 
-class LogReader {
+class LogReader : protected FileReader {
 public:
-  LogReader(size_t memory_pool_block_size = DEFAULT_EVENT_MEMORY_POOL_BLOCK_SIZE);
+  LogReader(bool local_cache = false, int chunk_size = -1, int retries = 0, size_t memory_pool_block_size = DEFAULT_EVENT_MEMORY_POOL_BLOCK_SIZE);
   ~LogReader();
-  bool load(const std::string &file);
+  bool load(const std::string &file, std::atomic<bool> *abort = nullptr);
 
   std::vector<Event*> events;
 
diff --git a/selfdrive/ui/replay/main.cc b/selfdrive/ui/replay/main.cc
index 2f417fc6a5..b0fe8eb3ad 100644
--- a/selfdrive/ui/replay/main.cc
+++ b/selfdrive/ui/replay/main.cc
@@ -1,20 +1,26 @@
-#include "selfdrive/ui/replay/replay.h"
-
-#include <csignal>
-#include <iostream>
 #include <termios.h>
 
 #include <QApplication>
 #include <QCommandLineParser>
 #include <QDebug>
 #include <QThread>
+#include <csignal>
+#include <iostream>
+
+#include "selfdrive/ui/replay/replay.h"
 
 const QString DEMO_ROUTE = "4cf7a6ad03080c90|2021-09-29--13-46-36";
 struct termios oldt = {};
+Replay *replay = nullptr;
 
 void sigHandler(int s) {
   std::signal(s, SIG_DFL);
-  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
+  if (oldt.c_lflag) {
+    tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
+  }
+  if (replay) {
+    replay->stop();
+  }
   qApp->quit();
 }
 
@@ -69,7 +75,7 @@ void keyboardThread(Replay *replay) {
   }
 }
 
-int main(int argc, char *argv[]){
+int main(int argc, char *argv[]) {
   QApplication app(argc, argv);
   std::signal(SIGINT, sigHandler);
   std::signal(SIGTERM, sigHandler);
@@ -78,6 +84,7 @@ int main(int argc, char *argv[]){
       {"dcam", REPLAY_FLAG_DCAM, "load driver camera"},
       {"ecam", REPLAY_FLAG_ECAM, "load wide road camera"},
       {"no-loop", REPLAY_FLAG_NO_LOOP, "stop at the end of the route"},
+      {"no-cache", REPLAY_FLAG_NO_FILE_CACHE, "turn off local cache"},
   };
 
   QCommandLineParser parser;
@@ -109,7 +116,7 @@ int main(int argc, char *argv[]){
       replay_flags |= flag;
     }
   }
-  Replay *replay = new Replay(route, allow, block, nullptr, replay_flags, parser.value("data_dir"), &app);
+  replay = new Replay(route, allow, block, nullptr, replay_flags, parser.value("data_dir"), &app);
   if (!replay->load()) {
     return 0;
   }
diff --git a/selfdrive/ui/replay/replay.cc b/selfdrive/ui/replay/replay.cc
index 67806f5560..5b17fd5e4a 100644
--- a/selfdrive/ui/replay/replay.cc
+++ b/selfdrive/ui/replay/replay.cc
@@ -5,8 +5,8 @@
 
 #include <capnp/dynamic.h>
 #include "cereal/services.h"
-#include "selfdrive/common/timing.h"
 #include "selfdrive/common/params.h"
+#include "selfdrive/common/timing.h"
 #include "selfdrive/hardware/hw.h"
 #include "selfdrive/ui/replay/util.h"
 
@@ -35,16 +35,21 @@ Replay::Replay(QString route, QStringList allow, QStringList block, SubMaster *s
 }
 
 Replay::~Replay() {
+  stop();
+  delete pm;
+  delete events_;
+}
+
+void Replay::stop() {
+  if (stream_thread_ == nullptr) return;
+
   qDebug() << "shutdown: in progress...";
   exit_ = updating_events_ = true;
-  if (stream_thread_) {
-    stream_cv_.notify_one();
-    stream_thread_->quit();
-    stream_thread_->wait();
-  }
+  stream_cv_.notify_one();
+  stream_thread_->quit();
+  stream_thread_->wait();
+  stream_thread_ = nullptr;
 
-  delete pm;
-  delete events_;
   segments_.clear();
   camera_server_.reset(nullptr);
   qDebug() << "shutdown: done";
@@ -91,6 +96,7 @@ void Replay::doSeek(int seconds, bool relative) {
     if (relative) {
       seconds += currentSeconds();
     }
+    seconds = std::max(0, seconds);
     int seg = seconds / 60;
     if (segments_.find(seg) == segments_.end()) {
       qInfo() << "can't seek to" << seconds << "s, segment" << seg << "is invalid";
@@ -134,26 +140,30 @@ void Replay::segmentLoadFinished(bool success) {
 void Replay::queueSegment() {
   if (segments_.empty()) return;
 
-  SegmentMap::iterator begin, cur, end;
-  begin = cur = end = segments_.lower_bound(std::min(current_segment_.load(), segments_.rbegin()->first));
-  // set fwd to 0 to just load the current segment when seeking to a new window.
-  const int fwd = cur->second == nullptr ? 0 : FORWARD_SEGS;
-  for (int i = 0; end != segments_.end() && i <= fwd; ++end, ++i) {
-    auto &[n, seg] = *end;
-    if (!seg) {
-      seg = std::make_unique<Segment>(n, route_->at(n), hasFlag(REPLAY_FLAG_DCAM), hasFlag(REPLAY_FLAG_ECAM));
-      QObject::connect(seg.get(), &Segment::loadFinished, this, &Replay::segmentLoadFinished);
-      qInfo() << "loading segment" << n << "...";
+  SegmentMap::iterator cur, end;
+  cur = end = segments_.lower_bound(std::min(current_segment_.load(), segments_.rbegin()->first));
+  for (int i = 0; end != segments_.end() && i <= FORWARD_SEGS; ++i) {
+    ++end;
+  }
+  // load one segment at a time
+  for (auto it = cur; it != end; ++it) {
+    if (!it->second) {
+      if (it == cur || std::prev(it)->second->isLoaded()) {
+        auto &[n, seg] = *it;
+        seg = std::make_unique<Segment>(n, route_->at(n), hasFlag(REPLAY_FLAG_DCAM), hasFlag(REPLAY_FLAG_ECAM), !hasFlag(REPLAY_FLAG_NO_FILE_CACHE));
+        QObject::connect(seg.get(), &Segment::loadFinished, this, &Replay::segmentLoadFinished);
+        qInfo() << "loading segment" << n << "...";
+      }
+      break;
     }
   }
-
   const auto &cur_segment = cur->second;
   enableHttpLogging(!cur_segment->isLoaded());
 
   // merge the previous adjacent segment if it's loaded
-  auto prev = segments_.find(cur_segment->seg_num - 1);
-  if (prev != segments_.end() && prev->second && prev->second->isLoaded()) {
-    begin = prev;
+  auto begin = segments_.find(cur_segment->seg_num - 1);
+  if (begin == segments_.end() || !(begin->second && begin->second->isLoaded())) {
+    begin = cur;
   }
   mergeSegments(begin, end);
 
@@ -168,9 +178,9 @@ void Replay::queueSegment() {
 }
 
 void Replay::mergeSegments(const SegmentMap::iterator &begin, const SegmentMap::iterator &end) {
-  // segments must be merged in sequence.
+  // merge 3 segments in sequence.
   std::vector<int> segments_need_merge;
-  for (auto it = begin; it != end && it->second->isLoaded(); ++it) {
+  for (auto it = begin; it != end && it->second->isLoaded() && segments_need_merge.size() < 3; ++it) {
     segments_need_merge.push_back(it->first);
   }
 
diff --git a/selfdrive/ui/replay/replay.h b/selfdrive/ui/replay/replay.h
index 5b5f7dfa8b..57d9b582d3 100644
--- a/selfdrive/ui/replay/replay.h
+++ b/selfdrive/ui/replay/replay.h
@@ -5,13 +5,15 @@
 #include "selfdrive/ui/replay/camera.h"
 #include "selfdrive/ui/replay/route.h"
 
-constexpr int FORWARD_SEGS = 2;
+// one segment uses about 100M of memory
+constexpr int FORWARD_SEGS = 5;
 
 enum REPLAY_FLAGS {
   REPLAY_FLAG_NONE = 0x0000,
   REPLAY_FLAG_DCAM = 0x0002,
   REPLAY_FLAG_ECAM = 0x0004,
   REPLAY_FLAG_NO_LOOP = 0x0010,
+  REPLAY_FLAG_NO_FILE_CACHE = 0x0020,
 };
 
 class Replay : public QObject {
@@ -23,6 +25,7 @@ public:
   ~Replay();
   bool load();
   void start(int seconds = 0);
+  void stop();
   void pause(bool pause);
   bool isPaused() const { return paused_; }
   inline bool hasFlag(REPLAY_FLAGS flag) { return flags_ & flag; };
diff --git a/selfdrive/ui/replay/route.cc b/selfdrive/ui/replay/route.cc
index 6338fd16e6..04ad7b2144 100644
--- a/selfdrive/ui/replay/route.cc
+++ b/selfdrive/ui/replay/route.cc
@@ -1,15 +1,19 @@
 #include "selfdrive/ui/replay/route.h"
 
+#include <QDir>
 #include <QEventLoop>
 #include <QJsonArray>
 #include <QJsonDocument>
 #include <QRegExp>
+#include <QtConcurrent>
 
 #include "selfdrive/hardware/hw.h"
 #include "selfdrive/ui/qt/api.h"
 #include "selfdrive/ui/replay/util.h"
 
-Route::Route(const QString &route, const QString &data_dir) : route_(parseRoute(route)), data_dir_(data_dir) {}
+Route::Route(const QString &route, const QString &data_dir) : data_dir_(data_dir) {
+  route_ = parseRoute(route);
+}
 
 RouteIdentifier Route::parseRoute(const QString &str) {
   QRegExp rx(R"(^([a-z0-9]{16})([|_/])(\d{4}-\d{2}-\d{2}--\d{2}-\d{2}-\d{2})(?:(--|/)(\d*))?$)");
@@ -41,7 +45,7 @@ bool Route::loadFromServer() {
 
 bool Route::loadFromJson(const QString &json) {
   QRegExp rx(R"(\/(\d+)\/)");
-  for (const auto &value :  QJsonDocument::fromJson(json.trimmed().toUtf8()).object()) {
+  for (const auto &value : QJsonDocument::fromJson(json.trimmed().toUtf8()).object()) {
     for (const auto &url : value.toArray()) {
       QString url_str = url.toString();
       if (rx.indexIn(url_str) != -1) {
@@ -86,10 +90,7 @@ void Route::addFileToSegment(int n, const QString &file) {
 
 // class Segment
 
-Segment::Segment(int n, const SegmentFile &files, bool load_dcam, bool load_ecam) : seg_num(n) {
-  static std::once_flag once_flag;
-  std::call_once(once_flag, [=]() { if (!CACHE_DIR.exists()) QDir().mkdir(CACHE_DIR.absolutePath()); });
-
+Segment::Segment(int n, const SegmentFile &files, bool load_dcam, bool load_ecam, bool local_cache) : seg_num(n) {
   // [RoadCam, DriverCam, WideRoadCam, log]. fallback to qcamera/qlog
   const QString file_list[] = {
       files.road_cam.isEmpty() ? files.qcamera : files.road_cam,
@@ -100,71 +101,34 @@ Segment::Segment(int n, const SegmentFile &files, bool load_dcam, bool load_ecam
   for (int i = 0; i < std::size(file_list); i++) {
     if (!file_list[i].isEmpty()) {
       loading_++;
-      QThread *t = new QThread();
-      QObject::connect(t, &QThread::started, [=]() { loadFile(i, file_list[i].toStdString()); });
-      loading_threads_.emplace_back(t)->start();
+      synchronizer_.addFuture(QtConcurrent::run([=] { loadFile(i, file_list[i].toStdString(), local_cache); }));
     }
   }
 }
 
 Segment::~Segment() {
-  aborting_ = true;
-  for (QThread *t : loading_threads_) {
-    if (t->isRunning()) {
-      t->quit();
-      t->wait();
-    }
-    delete t;
-  }
+  disconnect();
+  abort_ = true;
+  synchronizer_.setCancelOnWait(true);
+  synchronizer_.waitForFinished();
 }
 
-void Segment::loadFile(int id, const std::string file) {
-  const bool is_remote = file.find("https://") == 0;
-  const std::string local_file = is_remote ? cacheFilePath(file) : file;
-  bool file_ready = util::file_exists(local_file);
-
-  if (!file_ready && is_remote) {
-    file_ready = downloadFile(id, file, local_file);
-  }
-
-  if (!aborting_ && file_ready) {
-    if (id < MAX_CAMERAS) {
-      frames[id] = std::make_unique<FrameReader>();
-      success_ = success_ && frames[id]->load(local_file);
-    } else {
-      std::string decompressed = cacheFilePath(local_file + ".decompressed");
-      if (!util::file_exists(decompressed)) {
-        std::ofstream ostrm(decompressed, std::ios::binary);
-        readBZ2File(local_file, ostrm);
-      }
-      log = std::make_unique<LogReader>();
-      success_ = success_ && log->load(decompressed);
-    }
+void Segment::loadFile(int id, const std::string file, bool local_cache) {
+  bool success = false;
+  if (id < MAX_CAMERAS) {
+    frames[id] = std::make_unique<FrameReader>(local_cache, 20 * 1024 * 1024, 3);
+    success = frames[id]->load(file, &abort_);
+  } else {
+    log = std::make_unique<LogReader>(local_cache, -1, 3);
+    success = log->load(file, &abort_);
   }
 
-  if (!aborting_ && --loading_ == 0) {
-    emit loadFinished(success_);
+  if (!success) {
+    // abort all loading jobs.
+    abort_ = true;
   }
-}
-
-bool Segment::downloadFile(int id, const std::string &url, const std::string local_file) {
-  bool ret = false;
-  int retries = 0;
-  while (!aborting_) {
-    ret = httpMultiPartDownload(url, local_file, id < MAX_CAMERAS ? 3 : 1, &aborting_);
-    if (ret || aborting_) break;
 
-    if (++retries > max_retries_) {
-      qInfo() << "download failed after retries" << max_retries_;
-      break;
-    }
-    qInfo() << "download failed, retrying" << retries;
+  if (--loading_ == 0) {
+    emit loadFinished(!abort_);
   }
-  return ret;
-}
-
-std::string Segment::cacheFilePath(const std::string &file) {
-  QString url_no_query = QUrl(file.c_str()).toString(QUrl::RemoveQuery);
-  QString sha256 = QCryptographicHash::hash(url_no_query.toUtf8(), QCryptographicHash::Sha256).toHex();
-  return CACHE_DIR.filePath(sha256 + "." + QFileInfo(url_no_query).suffix()).toStdString();
 }
diff --git a/selfdrive/ui/replay/route.h b/selfdrive/ui/replay/route.h
index f0609c5ef3..14289cc4f1 100644
--- a/selfdrive/ui/replay/route.h
+++ b/selfdrive/ui/replay/route.h
@@ -1,14 +1,10 @@
 #pragma once
 
-#include <QDir>
-#include <QThread>
+#include <QFutureSynchronizer>
 
-#include "selfdrive/common/util.h"
 #include "selfdrive/ui/replay/framereader.h"
 #include "selfdrive/ui/replay/logreader.h"
 
-const QDir CACHE_DIR(util::getenv("COMMA_CACHE", "/tmp/comma_download_cache/").c_str());
-
 struct RouteIdentifier {
   QString dongle_id;
   QString timestamp;
@@ -49,9 +45,9 @@ class Segment : public QObject {
   Q_OBJECT
 
 public:
-  Segment(int n, const SegmentFile &files, bool load_dcam, bool load_ecam);
+  Segment(int n, const SegmentFile &files, bool load_dcam, bool load_ecam, bool local_cache);
   ~Segment();
-  inline bool isLoaded() const { return !loading_ && success_; }
+  inline bool isLoaded() const { return !loading_ && !abort_; }
 
   const int seg_num = 0;
   std::unique_ptr<LogReader> log;
@@ -61,12 +57,9 @@ signals:
   void loadFinished(bool success);
 
 protected:
-  void loadFile(int id, const std::string file);
-  bool downloadFile(int id, const std::string &url, const std::string local_file);
-  std::string cacheFilePath(const std::string &file);
+  void loadFile(int id, const std::string file, bool local_cache);
 
-  std::atomic<bool> success_ = true, aborting_ = false;
+  std::atomic<bool> abort_ = false;
   std::atomic<int> loading_ = 0;
-  std::vector<QThread*> loading_threads_;
-  const int max_retries_ = 3;
+  QFutureSynchronizer<void> synchronizer_;
 };
diff --git a/selfdrive/ui/replay/tests/test_replay.cc b/selfdrive/ui/replay/tests/test_replay.cc
index 4693a9807a..6e2ec15a34 100644
--- a/selfdrive/ui/replay/tests/test_replay.cc
+++ b/selfdrive/ui/replay/tests/test_replay.cc
@@ -1,31 +1,37 @@
-#include <QCryptographicHash>
 #include <QDebug>
 #include <QEventLoop>
+#include <fstream>
+#include <sstream>
 
 #include "catch2/catch.hpp"
+#include "selfdrive/common/util.h"
 #include "selfdrive/ui/replay/replay.h"
 #include "selfdrive/ui/replay/util.h"
 
 const QString DEMO_ROUTE = "4cf7a6ad03080c90|2021-09-29--13-46-36";
-std::string sha_256(const QString &dat) {
-  return QString(QCryptographicHash::hash(dat.toUtf8(), QCryptographicHash::Sha256).toHex()).toStdString();
-}
+const std::string TEST_RLOG_URL = "https://commadataci.blob.core.windows.net/openpilotci/0c94aa1e1296d7c6/2021-05-05--19-48-37/0/rlog.bz2";
+const std::string TEST_RLOG_CHECKSUM = "5b966d4bb21a100a8c4e59195faeb741b975ccbe268211765efd1763d892bfb3";
 
 TEST_CASE("httpMultiPartDownload") {
   char filename[] = "/tmp/XXXXXX";
   close(mkstemp(filename));
 
-  const char *stream_url = "https://commadataci.blob.core.windows.net/openpilotci/0c94aa1e1296d7c6/2021-05-05--19-48-37/0/rlog.bz2";
-  SECTION("5 connections") {
-    REQUIRE(httpMultiPartDownload(stream_url, filename, 5));
+  std::string content;
+  auto file_size = getRemoteFileSize(TEST_RLOG_URL);
+  REQUIRE(file_size > 0);
+  SECTION("5 connections, download to file") {
+    std::ofstream of(filename, of.binary | of.out);
+    REQUIRE(httpMultiPartDownload(TEST_RLOG_URL, of, 5, file_size));
+    content = util::read_file(filename);
   }
-  SECTION("1 connection") {
-    REQUIRE(httpMultiPartDownload(stream_url, filename, 1));
+  SECTION("5 connection, download to buffer") {
+    std::ostringstream oss;
+    content.resize(file_size);
+    oss.rdbuf()->pubsetbuf(content.data(), content.size());
+    REQUIRE(httpMultiPartDownload(TEST_RLOG_URL, oss, 5, file_size));
   }
-  std::string content = util::read_file(filename);
   REQUIRE(content.size() == 9112651);
-  std::string checksum = sha_256(QString::fromStdString(content));
-  REQUIRE(checksum == "e44edfbb545abdddfd17020ced2b18b6ec36506152267f32b6a8e3341f8126d6");
+  REQUIRE(sha256(content) == TEST_RLOG_CHECKSUM);
 }
 
 int random_int(int min, int max) {
@@ -35,13 +41,28 @@ int random_int(int min, int max) {
   return dist(rng);
 }
 
+TEST_CASE("FileReader") {
+  auto enable_local_cache = GENERATE(true, false);
+  std::string cache_file = cacheFilePath(TEST_RLOG_URL);
+  system(("rm " + cache_file + " -f").c_str());
+
+  FileReader reader(enable_local_cache);
+  std::string content = reader.read(TEST_RLOG_URL);
+  REQUIRE(sha256(content) == TEST_RLOG_CHECKSUM);
+  if (enable_local_cache) {
+    REQUIRE(sha256(util::read_file(cache_file)) == TEST_RLOG_CHECKSUM);
+  } else {
+    REQUIRE(util::file_exists(cache_file) == false);
+  }
+}
+
 TEST_CASE("Segment") {
   Route demo_route(DEMO_ROUTE);
   REQUIRE(demo_route.load());
   REQUIRE(demo_route.segments().size() == 11);
 
   QEventLoop loop;
-  Segment segment(0, demo_route.at(0), false, false);
+  Segment segment(0, demo_route.at(0), false, false, false);
   QObject::connect(&segment, &Segment::loadFinished, [&]() {
     REQUIRE(segment.isLoaded() == true);
     REQUIRE(segment.log != nullptr);
@@ -68,8 +89,8 @@ TEST_CASE("Segment") {
 
 // helper class for unit tests
 class TestReplay : public Replay {
-public:
-  TestReplay(const QString &route) : Replay(route, {}, {}) {}
+ public:
+  TestReplay(const QString &route, uint8_t flags = REPLAY_FLAG_NO_FILE_CACHE) : Replay(route, {}, {}, nullptr, flags) {}
   void test_seek();
   void testSeekTo(int seek_to);
 };
@@ -113,7 +134,7 @@ void TestReplay::test_seek() {
   QEventLoop loop;
   std::thread thread = std::thread([&]() {
     for (int i = 0; i < 100; ++i) {
-      testSeekTo(random_int(0, 5 * 60));
+      testSeekTo(random_int(0, 3 * 60));
     }
     loop.quit();
   });
@@ -122,7 +143,8 @@ void TestReplay::test_seek() {
 }
 
 TEST_CASE("Replay") {
-  TestReplay replay(DEMO_ROUTE);
+  auto flag = GENERATE(REPLAY_FLAG_NO_FILE_CACHE, REPLAY_FLAG_NONE);
+  TestReplay replay(DEMO_ROUTE, flag);
   REQUIRE(replay.load());
   replay.test_seek();
 }
diff --git a/selfdrive/ui/replay/util.cc b/selfdrive/ui/replay/util.cc
index d350c144b9..0560571474 100644
--- a/selfdrive/ui/replay/util.cc
+++ b/selfdrive/ui/replay/util.cc
@@ -1,42 +1,60 @@
 #include "selfdrive/ui/replay/util.h"
 
-#include <array>
+#include <bzlib.h>
+#include <curl/curl.h>
+#include <openssl/sha.h>
+
 #include <cassert>
+#include <iomanip>
 #include <iostream>
 #include <mutex>
 #include <numeric>
-
-#include <bzlib.h>
-#include <curl/curl.h>
+#include <sstream>
 
 #include "selfdrive/common/timing.h"
 #include "selfdrive/common/util.h"
 
+namespace {
+
+static std::atomic<bool> enable_http_logging = false;
+
 struct CURLGlobalInitializer {
   CURLGlobalInitializer() { curl_global_init(CURL_GLOBAL_DEFAULT); }
   ~CURLGlobalInitializer() { curl_global_cleanup(); }
 };
 
 struct MultiPartWriter {
-  int64_t offset;
-  int64_t end;
-  int64_t written;
-  FILE *fp;
+  size_t offset;
+  size_t end;
+  size_t written;
+  std::ostream *os;
 };
 
-static size_t write_cb(char *data, size_t size, size_t count, void *userp) {
+size_t write_cb(char *data, size_t size, size_t count, void *userp) {
   MultiPartWriter *w = (MultiPartWriter *)userp;
-  fseek(w->fp, w->offset, SEEK_SET);
-  fwrite(data, size, count, w->fp);
+  w->os->seekp(w->offset);
   size_t bytes = size * count;
+  w->os->write(data, bytes);
   w->offset += bytes;
   w->written += bytes;
   return bytes;
 }
 
-static size_t dumy_write_cb(char *data, size_t size, size_t count, void *userp) { return size * count; }
+size_t dumy_write_cb(char *data, size_t size, size_t count, void *userp) { return size * count; }
+
+std::string formattedDataSize(size_t size) {
+  if (size < 1024) {
+    return std::to_string(size) + " B";
+  } else if (size < 1024 * 1024) {
+    return util::string_format("%.2f KB", (float)size / 1024);
+  } else {
+    return util::string_format("%.2f MB", (float)size / (1024 * 1024));
+  }
+}
 
-int64_t getRemoteFileSize(const std::string &url) {
+} // namespace
+
+size_t getRemoteFileSize(const std::string &url) {
   CURL *curl = curl_easy_init();
   if (!curl) return -1;
 
@@ -52,40 +70,26 @@ int64_t getRemoteFileSize(const std::string &url) {
     std::cout << "Download failed: error code: " << res << std::endl;
   }
   curl_easy_cleanup(curl);
-  return res == CURLE_OK ? (int64_t)content_length : -1;
+  return content_length > 0 ? content_length : 0;
 }
 
-std::string formattedDataSize(size_t size) {
-  if (size < 1024) {
-    return std::to_string(size) + " B";
-  } else if (size < 1024 * 1024) {
-    return util::string_format("%.2f KB", (float)size / 1024);
-  } else {
-    return util::string_format("%.2f MB", (float)size / (1024 * 1024));
-  }
+std::string getUrlWithoutQuery(const std::string &url) {
+  size_t idx = url.find("?");
+  return (idx == std::string::npos ? url : url.substr(0, idx));
 }
 
-static std::atomic<bool> enable_http_logging = false;
-
 void enableHttpLogging(bool enable) {
   enable_http_logging = enable;
 }
 
-bool httpMultiPartDownload(const std::string &url, const std::string &target_file, int parts, std::atomic<bool> *abort) {
+bool httpMultiPartDownload(const std::string &url, std::ostream &os, int parts, size_t content_length, std::atomic<bool> *abort) {
   static CURLGlobalInitializer curl_initializer;
   static std::mutex lock;
   static uint64_t total_written = 0, prev_total_written = 0;
   static double last_print_ts = 0;
 
-  int64_t content_length = getRemoteFileSize(url);
-  if (content_length <= 0) return false;
-
-  // create a tmp sparse file
-  const std::string tmp_file = target_file + ".tmp";
-  FILE *fp = fopen(tmp_file.c_str(), "wb");
-  assert(fp);
-  fseek(fp, content_length - 1, SEEK_SET);
-  fwrite("\0", 1, 1, fp);
+  os.seekp(content_length - 1);
+  os.write("\0", 1);
 
   CURLM *cm = curl_multi_init();
 
@@ -94,8 +98,8 @@ bool httpMultiPartDownload(const std::string &url, const std::string &target_fil
   for (int i = 0; i < parts; ++i) {
     CURL *eh = curl_easy_init();
     writers[eh] = {
-        .fp = fp,
-        .offset = i * part_size,
+        .os = &os,
+        .offset = (size_t)(i * part_size),
         .end = i == parts - 1 ? content_length - 1 : (i + 1) * part_size - 1,
     };
     curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, write_cb);
@@ -126,9 +130,7 @@ bool httpMultiPartDownload(const std::string &url, const std::string &target_fil
       if (enable_http_logging && last_print_ts > 0) {
         size_t average = (total_written - prev_total_written) / ((ts - last_print_ts) / 1000.);
         int progress = std::min<int>(100, 100.0 * (double)written / (double)content_length);
-
-        size_t idx = url.find("?");
-        std::cout << "downloading " << (idx == std::string::npos ? url : url.substr(0, idx)) << " - " << progress << "% (" << formattedDataSize(average) << "/s)" << std::endl;
+        std::cout << "downloading " << getUrlWithoutQuery(url) << " - " << progress << "% (" << formattedDataSize(average) << "/s)" << std::endl;
       }
       prev_total_written = total_written;
       last_print_ts = ts;
@@ -160,32 +162,34 @@ bool httpMultiPartDownload(const std::string &url, const std::string &target_fil
   }
 
   curl_multi_cleanup(cm);
-  fclose(fp);
-
-  bool ret = complete == parts;
-  ret = ret && ::rename(tmp_file.c_str(), target_file.c_str()) == 0;
-  return ret;
+  return complete == parts;
 }
 
-bool readBZ2File(const std::string_view file, std::ostream &stream) {
-  std::unique_ptr<FILE, decltype(&fclose)> f(fopen(file.data(), "r"), &fclose);
-  if (!f) return false;
+std::string decompressBZ2(const std::string &in) {
+  if (in.empty()) return {};
 
-  int bzerror = BZ_OK;
-  BZFILE *bz_file = BZ2_bzReadOpen(&bzerror, f.get(), 0, 0, nullptr, 0);
-  if (!bz_file) return false;
+  bz_stream strm = {};
+  int bzerror = BZ2_bzDecompressInit(&strm, 0, 0);
+  assert(bzerror == BZ_OK);
 
-  std::array<char, 64 * 1024> buf;
+  strm.next_in = (char *)in.data();
+  strm.avail_in = in.size();
+  std::string out(in.size() * 5, '\0');
   do {
-    int size = BZ2_bzRead(&bzerror, bz_file, buf.data(), buf.size());
-    if (bzerror == BZ_OK || bzerror == BZ_STREAM_END) {
-      stream.write(buf.data(), size);
+    strm.next_out = (char *)(&out[strm.total_out_lo32]);
+    strm.avail_out = out.size() - strm.total_out_lo32;
+    bzerror = BZ2_bzDecompress(&strm);
+    if (bzerror == BZ_OK && strm.avail_in > 0 && strm.avail_out == 0) {
+      out.resize(out.size() * 2);
     }
   } while (bzerror == BZ_OK);
 
-  bool success = (bzerror == BZ_STREAM_END);
-  BZ2_bzReadClose(&bzerror, bz_file);
-  return success;
+  BZ2_bzDecompressEnd(&strm);
+  if (bzerror == BZ_STREAM_END) {
+    out.resize(strm.total_out_lo32);
+    return out;
+  }
+  return {};
 }
 
 void precise_nano_sleep(long sleep_ns) {
@@ -205,3 +209,16 @@ void precise_nano_sleep(long sleep_ns) {
     }
   }
 }
+
+std::string sha256(const std::string &str) {
+  unsigned char hash[SHA256_DIGEST_LENGTH];
+  SHA256_CTX sha256;
+  SHA256_Init(&sha256);
+  SHA256_Update(&sha256, str.c_str(), str.size());
+  SHA256_Final(hash, &sha256);
+  std::stringstream ss;
+  for (int i = 0; i < SHA256_DIGEST_LENGTH; i++) {
+    ss << std::hex << std::setw(2) << std::setfill('0') << (int)hash[i];
+  }
+  return ss.str();
+}
diff --git a/selfdrive/ui/replay/util.h b/selfdrive/ui/replay/util.h
index db7fa8483e..30a26c4314 100644
--- a/selfdrive/ui/replay/util.h
+++ b/selfdrive/ui/replay/util.h
@@ -4,7 +4,10 @@
 #include <ostream>
 #include <string>
 
+std::string sha256(const std::string &str);
 void precise_nano_sleep(long sleep_ns);
-bool readBZ2File(const std::string_view file, std::ostream &stream);
+std::string decompressBZ2(const std::string &in);
 void enableHttpLogging(bool enable);
-bool httpMultiPartDownload(const std::string &url, const std::string &target_file, int parts, std::atomic<bool> *abort = nullptr);
+std::string getUrlWithoutQuery(const std::string &url);
+size_t getRemoteFileSize(const std::string &url);
+bool httpMultiPartDownload(const std::string &url, std::ostream &os, int parts, size_t content_length, std::atomic<bool> *abort = nullptr);