Gradle seems to have no problem downloading ExoPlayer, but I maintain a Java library that uses Maven for dependency management, and the following dependency:

      <dependency>
         <groupId>com.google.android.exoplayer</groupId>
         <artifactId>exoplayer-core</artifactId>
         <version>2.12.2</version>
         <type>aar</type>
         <scope>provided</scope>
      </dependency>

produced the following error during mvn compile (or any other task that pulls dependencies):

The following artifacts could not be resolved: com.google.android.exoplayer:exoplayer-common:jar:2.12.2, com.google.android.exoplayer:exoplayer-extractor:jar:2.12.2

I could see via bintray's web interface that the files are there, so I dug further. This appears to be related to the pom files generated by Gradle. I can fix the problem by:

1. Editing the exoplayer-core pom file downloaded by Maven, adding the <type>aar</type> line to its exoplayer-common and exoplayer-extractor dependencies
2. Removing exoplayer-common and exoplayer-extractor directories from my local repository (so Maven doesn't think they're cached)
3. Rerunning the Maven task
4. Editing the newly downloaded exoplayer-extractor pom file, again adding <type>aar</type> to its exoplayer-common dependency
5. Running the Maven task one last time

I would expect having <packaging>aar</packaging> under the project element (as ExoPlayer poms do) to address this problem, but apparently not, at least for runtime-scoped dependencies.

Note that I didn't have this problem with 2.11.x—exoplayer-core doesn't have runtime dependencies on the other libraries in that version.