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VLC for Android

March 13, 2017

DiffUtil off the UI thread

Geoffrey Métais

As stated in the previous post, we do process all DiffUtil.DiffResult calculations in main thread to preserve adapter state consistency.
But in VLC, we have to deal with potentially HUGE datasets, so calculation could take some time.

Background calculation is mandatory then, and we have to preserve dataset consistency. I lost a few days trying different techniques then finally chose to stack updates within a queue and use it for all dataset operations, because it provides consistency safetyness.
I’ve been inspired by Jon F Hancock blog post to get this right.

To achieve background calculation and preserve data consistency, we now have to use our update() method for all dataset updates or manage the pending queue state manually.

Threading

update(list) method is now splitted in two, in order to allow queueing and recursivity:
update(list) which is now limited to queueing the new list and triggering internalUpdate(list) to do the actual job.

Notice all queue accesses or modifications are done in the main thread (for the same reasons that for dataset changes).

// Our queue with next dataset
private final ArrayDeque<Item[]> mPendingUpdates = new ArrayDeque<>();

@MainThread
void update(final ArrayList<Item> newList) {
    mPendingUpdates.add(newList);
    if (mPendingUpdates.size() == 1)
        internalUpdate(newList); //no pending update, let's go
}

//private method, called exclusively by update()
private void internalUpdate(final ArrayList<Item> newList) {
    VLCApplication.runBackground(new Runnable() {
        @Override
        public void run() {
            final DiffUtil.DiffResult result = DiffUtil.calculateDiff(new MediaItemDiffCallback(mDataset, newList), false);
            //back to main thread for the update
            VLCApplication.runOnMainThread(new Runnable() {
                @Override
                public void run() {
                    mDataset = newList;
                    result.dispatchUpdatesTo(BaseBrowserAdapter.this);
                    //We are done with this dataset
                    mPendingUpdates.remove();
                    //Process the next queued dataset if any
                    if (!mPendingUpdates.isEmpty())
                        internalUpdate(mPendingUpdates.peek());
                }
            });
        }
    });
}

For simple actions, like item insertion/removal, we must check the mPendingUpdates state. Either we handle it, either we use update(list) in order to respect the queue process we just set. So, we have to copy the most recent dataset, add/remove the item then call update(list).

Using mDataset as the current reference state can be a mistake, if mPendingUpdates is not empty, another dataset will be processed between mDataset and our new list with item added or removed. In this case, we have to peek the last list from mPendingUpdates.

@MainThread
void addItem(Item item) {
  ArrayList<Item> newList = new ArrayList<>(mPendingUpdates.isEmpty() ? mDataset : mPendingUpdates.peekLast());
  newList.add(item);
  update(newList);
}

For item removal, I’d recommend to just avoid calling it with position only, prefer to pass the item reference. Because the position value is likely to be wrong if there is a pending update at this time.

Skip queued updates

In case you can receive a bunch of updates while DiffUtil is calculating the DiffUtil.DiffResult, you get a stack of new datasets to process. Let’s skip to the last one: as we made sure they are consistent we can do it. That’s just factorizing the updates.
We have to clear the mPendingUpdates queue from all its elements but the last one.

Here is our current queue processing:

mPendingUpdates.remove();
if (!mPendingUpdates.isEmpty())
    internalUpdate(mPendingUpdates.peek());

Which becomes:

mPendingUpdates.remove();
if (!mPendingUpdates.isEmpty()) {
    if (mPendingUpdates.size() > 1) { // more than one update queued
        ArrayList<Item> lastList = mPendingUpdates.peekLast();
        mPendingUpdates.clear();
        mPendingUpdates.add(lastList);
    }
    internalUpdate(mPendingUpdates.peek());
}

Code factorization

Here is my base adapter class, dedicated to pending queue management. Children classes just need to call update(newList) for any update.
(I chose to not specify List<T> because I also use arrays)

public abstract class BaseQueuedAdapter <T, VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter<VH> {

    protected T mDataset;
    private final ArrayDeque<T> mPendingUpdates = new ArrayDeque<>();
    final Handler mHandler = new Handler(Looper.getMainLooper());

    @MainThread
    public boolean hasPendingUpdates() {
        return !mPendingUpdates.isEmpty();
    }

    @MainThread
    public T peekLast() {
        return mPendingUpdates.isEmpty() ? mDataset : mPendingUpdates.peekLast();
    }

    @MainThread
    public void update(final T items) {
        mPendingUpdates.add(items);
        if (mPendingUpdates.size() == 1)
            internalUpdate(items);
    }

    private void internalUpdate(final T newList) {
        new thread(new Runnable() {
            @Override
            public void run() {
                final DiffUtil.DiffResult result = DiffUtil.calculateDiff(new ItemDiffCallback(mDataList, newList), false);
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        mDataset = newList;
                        result.dispatchUpdatesTo(BaseQueuedAdapter.this);
                        processQueue();
                    }
                });
            }
        }).start();
    }

    @MainThread
    private void processQueue() {
        mPendingUpdates.remove();
        if (!mPendingUpdates.isEmpty()) {
            if (mPendingUpdates.size() > 1) {
                T lastList = mPendingUpdates.peekLast();
                mPendingUpdates.clear();
                mPendingUpdates.add(lastList);
            }
            internalUpdate(mPendingUpdates.peek());
        }
    }
}

My adapter class becomes:

public class MyAdapter extends BaseQueuedAdapter<List<Item>, MyAdapter.ViewHolder>

That’s it, we now have asynchronous and classy RecyclerView updates without extra boilerplate 😎

March 13, 2017 12:00 AM

March 03, 2017

Recyclerview++ with DiffUtil

Geoffrey Métais

DiffUtil is an AppCompat utility class developed to ease Recyclerview updates.

You just pass it the new dataset and current one and it automagically handles all the notifyItemRange* events to provide cool RecyclerView animations or subtle item updates (like a single progressbar update instead of the whole item layout rebinding).

Principles

  1. Provide your custom DiffUtil.Callback fed with the old and new datasets to the DiffUtil.calculateDiff method, and obtain a DiffUtil.DiffResult which contains all the necessary operations (additions, deletions and optionnally moves) to get from old list to the new one.
  2. Update your dataset
  3. Call diffResult.dispatchUpdatesTo(recyclerviewAdapter), your recyclerviewAdapter will receive all the corresponding notifyItemRange* events and benefit from shiny recyclerview animations!

It is strongly advised to run all dataset operations in the main thread, to ensure consistency. And for now (until next post), DiffUtil calculations will also be run in the main thread for consistency concern.

Basic usage

Here is a simple example of DiffUtil powered recyclerview update method in browsers adapter:

@MainThread
void update(final ArrayList<Item> newList) {
    final DiffUtil.DiffResult result = DiffUtil.calculateDiff(
                new MediaItemDiffCallback(mDataset, newList), false);
    mDataset = newList;
    result.dispatchUpdatesTo(MyAdapter.this);
}

You can see we only have these 3 basic steps.
With mDataset the current dataset, newList the new one, and false the parameter value for moves detection, we don’t handle it for now.

The base DiffUtil.Callback implementation we use:

public class MediaItemDiffCallback extends DiffUtil.Callback {
    protected Item[] oldList, newList;

    public MediaItemDiffCallback(Item[] oldList, Item[] newList) {
        this.oldList = oldList;
        this.newList = newList;
    }

    @Override
    public int getOldListSize() {
        return oldList == null ? 0 : oldList.length;
    }

    @Override
    public int getNewListSize() {
        return newList == null ? 0 : newList.length;
    }

    @Override
    public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
        return oldList[oldItemPosition].equals(newList[newItemPosition]);
    }

    @Override
    public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
        return true;
    }
}

For now, areContentsTheSame always returns true, we’ll see later how to use it for smarter updates. Let’s focus on areItemsTheSame: this is simply a equals-ish method to determine if two instances correspond to the same model view.

Now, with this diffResult, for every item insertion and deletion we get the precise adapter notification.
Typical application is list feeding, all new items are nicely inserted or removed which makes fancy animations to happen, like if we had set all the notifyItemInserted and notifyItemDeleted one by one.

A nicer use case is list/grid filtering. Here’s the result, with that simple update(newList) call:

video grid

Finer items updates

In video section, we want to update an item view if media progress or thumbnail has changed, but we don’t want to completely rebind its view.
Until VLC 2.0.6, you could experience a flicker of the video you were watching once getting back from video player. That’s because media progress had changed and we blindly updated the whole view (which triggered thumbnail reloading).

Here is the DiffUtil.Callback specific to video grid which not only checks if items are the same, but if their content has changed also:

private class VideoItemDiffCallback extends DiffUtil.Callback {
        List<Item> oldList, newList;
        VideoItemDiffCallback(List<Item> oldList, List<Item> newList) {
            this.oldList = oldList;
            this.newList = newList;
        }

        @Override
        public int getOldListSize() {
            return oldList == null ? 0 : oldList.size();
        }

        @Override
        public int getNewListSize() {
            return newList == null ? 0 : newList.size();
        }

        @Override
        public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
            return oldList.get(oldItemPosition).equals(newList.get(newItemPosition));
        }

        @Override
        public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
            Item oldItem = oldList.get(oldItemPosition);
            Item newItem = newList.get(newItemPosition);
            return oldItem.getTime() == newItem.getTime() &&
              TextUtils.equals(oldItem.getArtworkMrl(), newItem.getArtworkMrl());
        }

        @Nullable
        @Override
        public Object getChangePayload(int oldItemPosition, int newItemPosition) {
            Item oldItem = oldList.get(oldItemPosition);
            Item newItem = newList.get(newItemPosition);
            if (oldItem.getTime() != newItem.getTime())
                return UPDATE_TIME;
            else
                return UPDATE_THUMB;
        }
    }

If areItemsTheSame returns true, areContentsTheSame is called for the same items. areContentsTheSame returns false if we detect small changes we want to propagate to the UI without totally rebinding the concerned item view. In our case this is two Item instances representing the same video file but artwork URL or time value has changed.

If areContentsTheSame returns false, getChangePayload is called for the same items. We define here the updated value and return it. The dispatch util will call notifyItemChanged(position, payload) with this value. Then it’s up to the adapter to manage the update:

In the adapter, we override onBindViewHolder(holder, position, payload) to achieve this:

@Override
public void onBindViewHolder(ViewHolder holder, int position, List<Object> payloads) {
    if (payloads.isEmpty()) {
        onBindViewHolder(holder, position);
    } else {
        MediaWrapper media = mVideos.get(position);
        for (Object data : payloads) {
          switch ((int) data) {
            case UPDATE_THUMB:
                AsyncImageLoader.loadPicture(holder.thumbView, media);
                break;
            case UPDATE_TIME:
                fillView(holder, media);
                break;
          }
        }
    }
}

onBindViewHolder(holder, position, payloads) makes the smart move and updates the related view(s), instead of rebinding the whole item view. In our case, we load the thumb in the ImageView or we regenerate the progress string and update the progress bar with fillView().
As the dataSet is already updated, we don’t need to pass the values here, so I opted for constants refering to the different actions.

DiffUtil process scheme

flaw chart

Moves detection

The DiffUtil.calculateDiff algorithm can optionnally do a second pass to look for items movements between the old and new lists. If the sort order doesn’t change, it is useless to do it.
In VLC it’s only interesting in video grid for now, so we call:

DiffUtil.calculateDiff(new VideoItemDiffCallback(oldList, newList), detectMoves);

Where detectMoves variable is a boolean which is set to true only in case of video resorting call, in other cases we spare the second pass. Thanks to it, animations are fancier with only moving cards. Without this moves detection we’d get disappearing and reappearing cards.

Resorting videos with moves detection:

sort no move

Without moves detection:

sort moves

Going further

We now master diffutil, but we can do better and get calculation out of UI thread.
Rendez-vous to the second part of this post to check it out.

March 03, 2017 12:00 AM

February 23, 2017

Announcing VLC 2.1 beta release!

Geoffrey Métais

Not so much activity on Play Store since v2.0.6 release.
I’ve been quite busy but VLC keeps going on with very interesting evolutions!
This post will only deal with features, not their implementation. I will later publish other posts, more interesting for developers, about it.

2.1.x version name will be used for beta only, we’ll decide later which version the stable release will be.

To get it you need to join the beta program, and you’ll receive it like a normal update.

For now, let me introduce you to the new VLC for Android.

UX evolutions

Presentation

Video cards have been refactored, we now show you video informations over its cover picture. This is a nicer presentation and gives room for displaying more videos at once. Others lists view have been reworked too, like audio media, browsers and history. We got rid of cardview pattern, and got back to a more flat and clean design.

Audio lists have been a bit lifted too but this change is lighter.

Info page has also been redesigned with a fancy collapse effect for thumbnail or cover.

video grid

info panel info panel

New Audio Player Style

Audio player background is now a blurred version of current art cover if available.

player list player cover

Dynamic UI

Scrolling

The action bar will now hide when your scroll your media lists, to save the more useful space possible while you’re looking for your media.

list scroll

Album view has been revamped to become more #Material and now serves for playlists too

video grid

Updating content

Thanks to the DiffUtil tool from Appcompat library, grids/lists updates are now animated and more efficient.
One disturbing side effect is when you refresh and there’s no change in your media library. You won’t see any update, not even any flickering.
But the cool thing is whith actual content update, like during media scan or filtering the current view with the new search UX, insertions/deletions and position changes are animated:

video grid

TV design

TV interface had its own lifting too, nothing really impressive here. Colors are less depressive and we make long media titles scroll, I heard your (justified) frustration :)

The interesting new feature on TV is the Picture-In-Picture (aka PIP) mode, available for all Android TVs powered by Android 7+.
It’s really like our popup mode in classic phone/tablet interface (so we used the very same icon in video advanced options for PIP).
You can still watch your video while using another application.

video grid

audio player

360° Videos support

VLC now supports 360° videos, you can change viewpoint by swiping or with remote control arrows.

video 360

Cardboard/VR mode is not available yet but we are working on it.

Search has been splitted in two modes:

  • First step, the text you type in triggers a filtering in the current view. Exaclty like in current playlist view.

search filter

  • Then, if you want to do a global search, click on the SEARCH IN ALL MEDIALIBRARY button to show the new search activity. Which will bring detailed results grouped by video/artist/album/songs/genres/playlist

search global

Bonus: VLC will now be compatible with voice search.
Asking Google Now “Search game in VLC” will trigger a game search and show you this new search result screen.

search voice

Android Auto

This release will bring Android Auto compatibility.
You’ll be able to use VLC as your travel music player with easy browsing into you audio library, with the minimum possible distraction from driving.

auto list

auto main

auto menu

auto player

VLC also supports voice actions on Android Auto:
You can ask “play Daft Punk” and Google Assistant will recognize whether it’s an artist, an album or a song you’re asking for and trigger VLC to play it.

auto voice

Action mode

You can now select multiple items by long press on them (classic context menu is still available with the three dots icon) and enjoy actions like play it all or add selection to playlist
Actions available depend on media type and selection count.

This is very handy for starting or creating a playlist.

video grid

Miscellaneous new features

  • DayNight mode integration
  • Restored double/long click on remote play to skip songs
  • Removed sound lowering on notification
  • Force previous song on audioplayer swipe
  • Fix audioplayer layout for black theme and RTL
  • Save subtitles delay and optionally audio delay for each file.
  • Support for LG devices with 18:9 aspect ratio

Under the hood

MediaLibrary

That’s the most important change in this update, because it affects the whole application, but you should barely notice it…

VLC now uses medialibrary like VLC for Tizen, others VLC ports will follow.
It’s a C++ library, written by Hugo Beauzée-Luyssen, which parses storages for video/audio files and manages a sqlite database to model your media library (with album, artist, genre classification, etc..). It replaces the old system we had on Android which just saved media files with their metadata, we had no proper structure for media library.
So these categories listing are now faster, we don’t have to generate categories at runtime. And this is all native code, which is faster than Java.
Beside this speed improvement, one of the main benefits of this medialibrary is to provide better search results

For now we are focusing on the first scan performance to make it at least as fast as the previous system.

So, this library is aimed to be a common module of all VLC ports, wich means all debugging, performance and any improvement will benefit other platforms.

Next steps for this library will be media scrapping, and network scan:

  • Medialibrary will get informations and illustrations for your media, so we’ll be able to present you a nice collection, and not files list anymore. We will also group media by shows/seasons et genre/release year/whatever
  • You will be able to scan your NAS content to access your media easily.

Playback performance & formats support

VLC core team worked hard too to bring performance improvements and some new features. Here are some highlights:

  • 360° videos support
  • Adaptive (HLS/Dash) & TS playback improved
  • OpenGLES 2.0 is now used to render video (for software decoders & mediacodec)
  • Support for VP8/9/10 in MP4
  • e-AC3 HDMI passthrough

Future

We also plan to implement a feature to download media on your device, in order to sync your series episodes or songs from your NAS to your device.

We’d like to support videos playlists like we do with videos grouped by their common name prefix.

As previously stated, medialibrary will allow to make VLC a real media center with fancy movies/tv shows presentation, and better artists/albums illustrations.

At last, I started an extension API in order for everyone to develop android applications which will provide content to VLC. For example, we will release (with sources of course) extensions bringing support of podcasts subscriptions and Google Drive access.

February 23, 2017 12:00 AM

February 22, 2017

Tips for VLC

Geoffrey Métais

Here are some hidden features of VLC on Android.

STOP playback service

There are 2 ways to completely stop vlc player service (and not just pause playback), but this action has no explicit button.

  • With mini player: long press on play/pause button stop player
  • With playback icon: only when playback is paused
    • on Android 5+: you can swipe the notification.
    • on Android 4.x: you should have a ‘x’ button on top-right corner. stop notification

Repeat video

With version 2.1 you’ll have the repeat button available in the video player advanced options, but you can already do that with version 2.0.x:
Long press on play/pause button to switch playback to repeat mode so your video playback will loop

Reorder media in current playlist

Simply drag media within current playlist to reorder it.

reorder playlist

Load last playlist

In action bar, the circled play button triggers loading of last playlist from the current category: In video view it will load last video(s) played, in Audio view it will load last audio playlist.

load last audio playlist

With remote play/pause control (wired headset or bluetooth ad2p device) when VLC is not playing, you can load last audio playlist and continue playback where you stopped it.

Next/previous by swipe

Swipe miniplayer on left/right triggers skip to previous/next media.

swipe next

Video player bindings

If you have a keyboard or a gamepad connected to your Android device, here are the key bindings in video player:

within DVD menu:

Key(s) Action
↓↑←→ navigate
Gamepad A or X /play/pause/space/OK/enter click on focused item

in 360° video playback (version 2.1.0+):

Key(s) Action
↓↑←→ change viewpoint

normal case:

Key(s) Action
F/fast_forward/→ seek (+10 seconds)
R/rewind/← seek (-10 seconds)
R1 seek (+1 minute)
L1 seek (-1 minute)
A(gamepad)/play/pause/space/OK toggle play/pause
O/Y(gamepad)/menu/↑ show advanced options
V/audio-track/X(gamepad) open subtitles options
N show DVD navigation menu
A resize video
M/mute toggle sound mute
S/STOP stop playback & exit player
captions select subtitles
J delay audio (-50ms)
K delay audio (+50ms)
G delay subtitles (-50ms)
H delay subtitles (+50ms)

February 22, 2017 12:00 AM

January 23, 2017

LAVA events

Rémi Duraffort

For some releases now, LAVA server is publishing events every time:

  • a Job status change (Submitted, Running, ...)
  • a Device status change (Idle, Reserved, ...)

The stream of events is public and anyone can subscribe and receive updates.

A dump of the streams for the production and the staging instances is available …

January 23, 2017 08:25 AM

January 19, 2017

Testing LAVA with DummySys

Rémi Duraffort

For more than 3 years now, I have been working on LAVA. Looking at the documentation:

LAVA is an automated validation architecture primarily aimed at testing deployments of systems based around the Linux kernel on ARM devices, specifically ARMv7 and later.

In order to test LAVA, you need:

  • a wide …

January 19, 2017 09:21 AM

September 21, 2016

Other uses of futex

Rémi Denis-Courmont

Revisiting the condition variable with futex and pondering thread synchronization primitives.

September 21, 2016 03:05 PM