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Jorge Ruesga bb7cab0cfd
Cea708Decoder: Honor service block size
The current implementation of ExoPlayer Cea708 is processing the whole service block without
taking into account the defined service block size, which could cause the execution of
unwanted command.

The following set of Cea708 represents a real use case of the above.

``` hex
FC9420FD152FFF0929FE8CFCFE9818FEE332FE731FFE1044FE8B03FE8CFCFE0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC942CFD1520FF4649FE8CFEFE9918FEE332FE731FFE1000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC942FFD9470FF8924FE8B03FE8CFCFE4A92FE0300FE9005FE0091FE2A00FE0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC9420FD97A1FFC829FE8CFEFE9918FEE332FE731FFE1043FE9203FE0100FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC94D6FDCEEFFF082AFE9202FE0C90FE0500FE912AFE0000FE424EFE6F00FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FCC168FD20F4FF4422FE4168FE4220FE7400FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC2C20FDE520FF8422FE2C20FE4265FE2000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC64EFFD70EFFFC422FE646FFE4270FE6F00FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC6EA7FD6E67FF0422FE6E27FE426EFE6700FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FCF420FD6173FF4422FE7420FE4261FE7300FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FC67E5FD206DFF8422FE6765FE4220FE6D00FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
FCF480FD7579FFC422FE7403FE4275FE7900FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000FA0000
```

The above frames should be displaying the following text on the screen (or at least the first part of it).

```
Ah, don't get
all sappy about it
```

ExoPlayer is currently parsing this block as follow (in parentheses the defined service block size):

```
(2) 22416842207400
G0 A
G0 h
G0 B
G0 \u0020
G0 t
C0 COMMAND_NUL

(2) 222C2042652000
G0 ,
G0 \u0020
G0 B
G0 e
G0 \u0020
C0 COMMAND_NUL

(2) 22646F42706F00
G0 d
G0 o
G0 B
G0 p
G0 o
C0 COMMAND_NUL

(2) 226E27426E6700
G0 n
G0 '
G0 B
G0 n
G0 g
C0 COMMAND_NUL

(2) 22742042617300
G0 t
G0 \u0020
G0 B
G0 a
G0 s
C0 COMMAND_NUL

(2) 22676542206D00
G0 g
G0 e
G0 B
G0 \u0020
G0 m
C0 COMMAND_NUL

(2) 22740342757900
G0 t
C0 COMMAND_ETX
G0 B
G0 u
G0 y
C0 COMMAND_NUL

(2) 2392030C4220730000
C1 COMMAND_SPL
G0 B
G0 \u0020
G0 s
C0 COMMAND_NUL
C0 COMMAND_NUL

(2) 22616C42656E00
G0 a
G0 l
G0 B
G0 e
G0 n
C0 COMMAND_NUL
```

So it ended up processing the following cue text (additional unwanted commands could be executed as well)

```
AhB t, Be doBpon'Bngt BasgeB mt
BuyB salBen
```

If instead the parsing logic take into account the service block size

```
(2) 22416842207400
G0 A
G0 h

(2) 222C2042652000
G0 ,
G0 \u0020

(2) 22646F42706F00
G0 d
G0 o

(2) 226E27426E6700
G0 n
G0 '

(2) 22742042617300
G0 t
G0 \u0020

(2) 22676542206D00
G0 g
G0 e

(2) 22740342757900
G0 t
C0 COMMAND_ETX

(2) 2392030C4220730000
C1 COMMAND_SPL

(2) 22616C42656E00
G0 a
G0 l
```

which is translated to (again I didn't processed all the frames, just a few of them)

```
Ah, don't get
al
```

which is what we are looking for.

This PR modifies service block parsing logic to honor service block size instead of read the full service block buffer.

Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
2022-02-02 16:53:54 +00:00
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ExoPlayer

ExoPlayer is an application level media player for Android. It provides an alternative to Androids MediaPlayer API for playing audio and video both locally and over the Internet. ExoPlayer supports features not currently supported by Androids MediaPlayer API, including DASH and SmoothStreaming adaptive playbacks. Unlike the MediaPlayer API, ExoPlayer is easy to customize and extend, and can be updated through Play Store application updates.

Documentation

Using ExoPlayer

ExoPlayer modules can be obtained from the Google Maven repository. It's also possible to clone the repository and depend on the modules locally.

From the Google Maven repository

1. Add ExoPlayer module dependencies

The easiest way to get started using ExoPlayer is to add it as a gradle dependency in the build.gradle file of your app module. The following will add a dependency to the full library:

implementation 'com.google.android.exoplayer:exoplayer:2.X.X'

where 2.X.X is your preferred version.

As an alternative to the full library, you can depend on only the library modules that you actually need. For example the following will add dependencies on the Core, DASH and UI library modules, as might be required for an app that only plays DASH content:

implementation 'com.google.android.exoplayer:exoplayer-core:2.X.X'
implementation 'com.google.android.exoplayer:exoplayer-dash:2.X.X'
implementation 'com.google.android.exoplayer:exoplayer-ui:2.X.X'

When depending on individual modules they must all be the same version.

The available library modules are listed below. Adding a dependency to the full ExoPlayer library is equivalent to adding dependencies on all of the library modules individually.

  • exoplayer-core: Core functionality (required).
  • exoplayer-dash: Support for DASH content.
  • exoplayer-hls: Support for HLS content.
  • exoplayer-rtsp: Support for RTSP content.
  • exoplayer-smoothstreaming: Support for SmoothStreaming content.
  • exoplayer-transformer: Media transformation functionality.
  • exoplayer-ui: UI components and resources for use with ExoPlayer.

In addition to library modules, ExoPlayer has extension modules that depend on external libraries to provide additional functionality. Some extensions are available from the Maven repository, whereas others must be built manually. Browse the extensions directory and their individual READMEs for details.

More information on the library and extension modules that are available can be found on the Google Maven ExoPlayer page.

2. Turn on Java 8 support

If not enabled already, you also need to turn on Java 8 support in all build.gradle files depending on ExoPlayer, by adding the following to the android section:

compileOptions {
  targetCompatibility JavaVersion.VERSION_1_8
}

3. Enable multidex

If your Gradle minSdkVersion is 20 or lower, you should enable multidex in order to prevent build errors.

Locally

Cloning the repository and depending on the modules locally is required when using some ExoPlayer extension modules. It's also a suitable approach if you want to make local changes to ExoPlayer, or if you want to use a development branch.

First, clone the repository into a local directory and checkout the desired branch:

git clone https://github.com/google/ExoPlayer.git
cd ExoPlayer
git checkout release-v2

Next, add the following to your project's settings.gradle file, replacing path/to/exoplayer with the path to your local copy:

gradle.ext.exoplayerModulePrefix = 'exoplayer-'
apply from: file("path/to/exoplayer/core_settings.gradle")

You should now see the ExoPlayer modules appear as part of your project. You can depend on them as you would on any other local module, for example:

implementation project(':exoplayer-library-core')
implementation project(':exoplayer-library-dash')
implementation project(':exoplayer-library-ui')

Developing ExoPlayer

Project branches

  • Development work happens on the dev-v2 branch. Pull requests should normally be made to this branch.
  • The release-v2 branch holds the most recent release.

Using Android Studio

To develop ExoPlayer using Android Studio, simply open the ExoPlayer project in the root directory of the repository.