Motown: Add examples/media_test, a command line media player app.

examples/media_test/media_test_app.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <deque>
+#include <iomanip>
+#include <iostream>
+
+#include "base/bind.h"
+#include "examples/media_test/keystroke.h"
+#include "examples/media_test/media_test.h"
+#include "mojo/application/application_runner_chromium.h"
+#include "mojo/public/c/system/main.h"
+#include "mojo/public/cpp/application/application_connection.h"
+#include "mojo/public/cpp/application/application_delegate.h"
+#include "mojo/public/cpp/application/application_impl.h"
+
+namespace examples {
+
+class MediaTestApp : public mojo::ApplicationDelegate {
+ public:
+  MediaTestApp() {}
+
+  ~MediaTestApp() override {}
+
+  // ApplicationDelegate implementation.
+  void Initialize(mojo::ApplicationImpl* app) override {
+    app_ = app;
+    ProcessArgs(app->args());
+
+    std::cerr << std::endl << "MEDIA TEST" << std::endl << std::endl;
+
+    if (input_file_names_.empty()) {
+      std::cerr << "Please provide the names of the files you want to play;"
+          << " for example:" << std::endl;
+      std::cerr << "mojo/devtools/common/mojo_run \\" << std::endl;
+      std::cerr << "    \"https://core.mojoapps.io/media_test.mojo \\"
+          << std::endl;
+      std::cerr << "    file:///usr/local/google/home/you/superstition.ogg \\"
+          << std::endl;
+      std::cerr << "    file:///usr/local/google/home/you/higherground.ogg\""
+          << std::endl << std::endl;
+      base::MessageLoop::current()->Quit();
+      return;
+    }
+
+    std::cerr << "    <enter>         play/pause" << std::endl;
+    std::cerr << "    n<enter>        next file" << std::endl;
+    std::cerr << "    p<enter>        previous file" << std::endl;
+    std::cerr << "    <digit><enter>  seek (0% - 90%)" << std::endl;
+    std::cerr << "    q<enter>        quit" << std::endl << std::endl;
+
+    if (paint_) {
+      std::cerr << "    duration   <none>" << std::endl;
+      std::cerr << "    title      <none>" << std::endl;
+      std::cerr << "    artist     <none>" << std::endl;
+      std::cerr << "    album      <none>" << std::endl;
+      std::cerr << "    publisher  <none>" << std::endl;
+      std::cerr << "    genre      <none>" << std::endl;
+      std::cerr << "    composer   <none>" << std::endl << std::endl;
+      std::cerr << std::endl << std::endl << kUp << std::flush;
+    } else {
+      std::cerr << std::endl;
+    }
+
+    CreateNewMediaTest();
+    Poll();
+  }
+
+  bool ConfigureIncomingConnection(
+      mojo::ApplicationConnection* connection) override {
+    return true;
+  }
+
+ private:
+  const char *kHome = "\r";
+  const char *kClearLine = "\033[K";
+  const char *kUp = "\033[A";
+  const double ns_per_second = 1000000000.0;

[johngro, 2016/03/21 22:10:47]

static constexpr for these.  Don't forget to declare storage 

Same comment as was made in the key input helper function, this is going to be
brittle from a portability perspective.  If this was the path we were going to
pursue moving forward, I would ask that these magic values get wrapped up as
static constexprs in some form of input class.

That said, I think the way forward is to integrate with Mozart, so re-organizing
this is probably moot.

[dalesat, 2016/03/21 23:58:35]

Done.

+
+  // Processes arguments.
+  void ProcessArgs(const std::vector<std::string>& args) {
+    if (args.size() <= 1) {
+      return;
+    }
+
+    for (std::string arg : args) {

[johngro, 2016/03/21 22:10:47]

probably should be const std::string& or const auto&, but see below.

[dalesat, 2016/03/21 23:58:35]

Done.

+      if (arg == "--paint") {
+        paint_ = true;
+      } else if (arg == "--no-paint") {
+        paint_ = false;
+      } else {
+        input_file_names_.push_back(arg);
+      }
+    }
+
+    input_file_names_.pop_front();

[johngro, 2016/03/21 22:10:47]

instead of doing this, why not just

for (size_t i = 1; i < args.size(); ++i) {
   const std::string& arg = args[i]
   // do good things
}

This also eliminates the need for the args.size() check above, and ensures that
input_file_names_iter_ (below) will always be properly initialized.

[dalesat, 2016/03/21 23:58:35]

Done.

+
+    input_file_names_iter_ = input_file_names_.begin();

[johngro, 2016/03/21 22:10:47]

see above; this variable will not be initialized by this method if args.size()
is <= 1.

[dalesat, 2016/03/21 23:58:35]

Acknowledged.

+  }
+
+  // Creates a new MediaTest object to play the file referenced by
+  // input_file_names_iter_.
+  void CreateNewMediaTest() {

[johngro, 2016/03/21 22:10:47]

DCHECK(input_file_names_iter_ != input_file_names.end());

[dalesat, 2016/03/21 23:58:35]

Done.

+    media_test_ = MediaTest::Create(app_, *input_file_names_iter_);
+
+    metadata_shown_ = false;
+    media_test_->RegisterUpdateCallback([this]() {

[johngro, 2016/03/21 22:10:47]

I really think that this lambda belongs in its own method (which the lambda
simply thunks to).

[dalesat, 2016/03/21 23:58:35]

Done.

+      if (media_test_->state() == mojo::media::MediaState::ENDED) {
+        // MediaTest doesn't appreciate being deleted in this callback.
+        // Next time Poll runs, we move on to the next file.
+        play_next_ = true;

[johngro, 2016/03/21 22:10:47]

consider posting a message to yourself in order to advance the track instead of
relying on Poll.

[dalesat, 2016/03/21 23:58:35]

Done.

+      }
+
+      const mojo::media::MediaMetadataPtr& metadata = media_test_->metadata();
+
+      if (metadata) {
+        duration_ns_ = metadata->duration;
+      }
+
+      if (paint_) {
+        std::cerr << kHome
+            << kUp << kUp << kUp<< kUp << kUp << kUp << kUp << kUp << kUp;

[johngro, 2016/03/21 22:10:47]

This is a bit nasty.  While I understand the lack of Mozart, and the example-ish
nature of this code, it would still be good to put a comment here explaining
what is going on (and why there are 9 kUps delivered, not 8, 10 or some other
number)

Also, ' ' after the 3rd kUp

[dalesat, 2016/03/21 23:58:35]

Done.

+      }
+
+      if (!paint_ && metadata_shown_) {
+        // Do nothing.
+      } else if (metadata) {
+        metadata_shown_ = true;
+        std::cerr << "    duration   " << std::setprecision(1) <<
+            double(metadata->duration) / ns_per_second << " seconds"
+            << clear_line() << std::endl;
+        std::cerr << "    title      " <<
+            (metadata->title ? metadata->title : "<none>")
+            << clear_line() << std::endl;
+        std::cerr << "    artist     " <<
+            (metadata->artist ? metadata->artist :  "<none>")
+            << clear_line() << std::endl;
+        std::cerr << "    album      " <<
+            (metadata->album ? metadata->album : "<none>")
+            << clear_line() << std::endl;
+        std::cerr << "    publisher  " <<
+            (metadata->publisher ? metadata->publisher : "<none>")
+            << clear_line() << std::endl;
+        std::cerr << "    genre      " <<
+            (metadata->genre ? metadata->genre : "<none>")
+            << clear_line() << std::endl;
+        std::cerr << "    composer   " <<
+            (metadata->composer ? metadata->composer : "<none>")
+            << clear_line() << std::endl << std::endl;
+      } else {
+        std::cerr << "    duration   <none>" << kClearLine << std::endl;
+        std::cerr << "    title      <none>" << kClearLine << std::endl;
+        std::cerr << "    artist     <none>" << kClearLine << std::endl;
+        std::cerr << "    album      <none>" << kClearLine << std::endl;
+        std::cerr << "    publisher  <none>" << kClearLine << std::endl;
+        std::cerr << "    genre      <none>" << kClearLine << std::endl;
+        std::cerr << "    composer   <none>" << kClearLine << std::endl;
+        std::cerr << std::endl;
+      }
+      std::cerr << "    " << state_string() << clear_line() << std::endl;
+    });
+
+    media_test_->Play();
+  }
+
+  // Returns a string describing the MediaTest object's state.
+  const char* state_string() const {
+    switch (media_test_->state()) {
+      case mojo::media::MediaState::FAULT:
+        return "FAULT";

[johngro, 2016/03/21 22:10:47]

perhaps put this case at the bottom, grouped with a default: for extra
insurance.

That, or everyone who calls state_string() needs to be on their guard for
possibly getting nullptr

[dalesat, 2016/03/21 23:58:35]

Never returning nullptr is a good idea, thanks.

I like that there's no default. The build fails if I add a state and don't have
a case for it.

[johngro, 2016/03/22 16:56:35]

Acknowledged.

+      case mojo::media::MediaState::UNPREPARED:
+        return "unprepared";
+      case mojo::media::MediaState::PAUSED:
+        return "paused";
+      case mojo::media::MediaState::PLAYING:
+        return "playing";
+      case mojo::media::MediaState::ENDED:
+        return "ended";
+    }
+    return nullptr;
+  }
+
+  // Handles a keystroke.
+  void HandleKeystroke(char keystroke) {
+    switch (keystroke) {
+      case '\n':
+        TogglePlayPause();
+        break;
+      case 'q':
+        base::MessageLoop::current()->Quit();
+        quit_ = true;
+        if (paint_) {
+          std::cerr << kHome << kUp << "    quitting" << kClearLine << std::endl
+              << kClearLine << std::endl;
+        } else {
+          std::cerr << "    quitting" << std::endl;
+        }
+        break;
+      case 'n':
+        if (++input_file_names_iter_ == input_file_names_.end()) {
+          input_file_names_iter_ = input_file_names_.begin();
+        }
+        CreateNewMediaTest();
+        break;
+      case 'p':
+        if (input_file_names_iter_ == input_file_names_.begin()) {
+          input_file_names_iter_ = input_file_names_.end();
+        }
+        input_file_names_iter_--;
+        CreateNewMediaTest();
+        break;
+      case '0':
+      case '1':
+      case '2':
+      case '3':
+      case '4':
+      case '5':
+      case '6':
+      case '7':
+      case '8':
+      case '9': {
+        int64_t position_ns = ((keystroke - '0') / 10.0) * duration_ns_;
+        media_test_->Seek(position_ns);
+        if (!paint_) {
+          std::cerr << "    seeking to " << std::fixed << std::setprecision(1)
+              << double(position_ns) / ns_per_second
+              << " seconds  " << std::endl;
+        }
+        break;
+      }
+    }
+  }
+
+  // Toggles between play and pause (prepared) states.
+  void TogglePlayPause() {
+    switch (media_test_->state()) {
+      case mojo::media::MediaState::PAUSED:
+        media_test_->Play();
+        break;
+      case mojo::media::MediaState::PLAYING:
+        media_test_->Pause();
+        break;
+      case mojo::media::MediaState::ENDED:
+        if (input_file_names_.size() == 1) {
+          // Replaying the only file. Reuse the same MediaTest instance.
+          media_test_->Seek(0);
+          media_test_->Play();
+        } else {
+          // Starting a new file. Create a new MediaTest instance.
+          CreateNewMediaTest();
+        }
+        break;
+      default:
+        break;
+    }
+  }
+
+  // Does any needed work and schedules itself to run again soon. Quits when
+  // quit_ is true.
+  void Poll() {
+    char keystroke = Keystroke();
+    if (keystroke != 0) {
+      HandleKeystroke(keystroke);
+    }

[johngro, 2016/03/21 22:10:47]

right now, Poll seems to be a necessary evil in order to make the keyboard go,
but tasks like moving to the next track and could be handled just by posting
messages (and avoid the 0-100mSec processing delay).

Given how difficult it is to take back a message after it has been queued (even
if it immediately becomes no longer relevant because of, say, they very next
keystroke waiting in the input queue) it may be the right idea to keep the
Poll/advance-state-machine style expressed here.  Still, actions like track
advance and quit could just post Poll callback.

Someday, when the switch to Mozart can be made, all of the Poll-ing can be
eliminated.

[dalesat, 2016/03/21 23:58:35]

Agreed. I switched to posting a task for play_next_ as you recommended. Some of
the stuff handled here should ideally be handled in other ways, but the position
update really requires polling. Because we're using a transform for the position
rather than some callback, we need to poll at the resolution of the position
display (100ms in this case).

+
+    if (quit_) {

[johngro, 2016/03/21 22:10:47]

this quit_ check should probably be first.  We should not be HandleKeystroke-ing
when it is time to quit.

[dalesat, 2016/03/21 23:58:35]

HandleKeystroke sets quit_, so this is the best we can do in terms of getting
out after the 'q' is detected. quit_ is false at the top of this method (added a
DCHECK), and Poll will never run again after this block runs.

+      // Eat the any additional keystrokes, which would otherwise make it to the
+      // command shell.
+      while (Keystroke() != 0) {
+        // Do nothing.
+      }
+      return;
+    }
+
+    if (play_next_) {
+      play_next_ = false;
+      if (++input_file_names_iter_ == input_file_names_.end()) {
+        input_file_names_iter_ = input_file_names_.begin();
+      } else {
+        CreateNewMediaTest();
+      }
+    }
+
+    if (paint_) {
+      std::cerr << kHome << "    " << std::fixed << std::setprecision(1)
+          << double(media_test_->position_ns()) / ns_per_second
+          << " seconds  " << kClearLine << std::flush;
+    }
+
+    base::MessageLoop::current()->PostDelayedTask(
+        FROM_HERE,
+        base::Bind(&MediaTestApp::Poll, base::Unretained(this)),
+        base::TimeDelta::FromMilliseconds(100));
+  }
+
+  const char* clear_line() const {
+    return paint_ ? kClearLine : "";
+  }
+
+  mojo::ApplicationImpl* app_;
+  std::unique_ptr<MediaTest> media_test_;
+  std::deque<std::string> input_file_names_;
+  decltype(input_file_names_.begin()) input_file_names_iter_;
+  bool play_next_ = false;
+  bool quit_ = false;
+  bool paint_ = true;
+  bool metadata_shown_ = false;
+  uint64_t duration_ns_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaTestApp);
+};
+
+}  // namespace examples
+
+MojoResult MojoMain(MojoHandle application_request) {
+  mojo::ApplicationRunnerChromium runner(new examples::MediaTestApp);
+  return runner.Run(application_request);
+}