android - 任何人都有 MediaPlayer 使用 ParcelFileDescriptor 和 createPipe()？

Question

与 my recent question on MediaRecorder and createPipe() 相关，并在 this other SO question 中讨论了 createPipe() 技术，我现在正试图让 MediaPlayer 通过 ParcelFileDescriptor 和 createPipe() 处理由 ContentProvider 提供的内容.

This sample project有我迄今为止的工作。它基于 an earlier sample that plays an OGG clip stored as a raw resource .因此，我知道我的剪辑很好。

我已将 MediaPlayer 设置更改为:

  private void loadClip() {
    try {
      mp=new MediaPlayer();
      mp.setDataSource(this,
                       PipeProvider.CONTENT_URI.buildUpon()
                                               .appendPath("clip.ogg")
                                               .build());
      mp.setOnCompletionListener(this);
      mp.prepare();
    }
    catch (Exception e) {
      goBlooey(e);
    }
  }

通过登录 PipeProvider，我看到我的 Uri 正在正确构建。

PipeProvider 与 this sample project 中的相同，它适用于向 Adob​​e Reader 提供 PDF 文件，这限制了我的代码可能被搞砸的程度。 :-)

具体来说，openFile() 从 ParcelFileDescriptor 创建一个管道:

  @Override
  public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
    ParcelFileDescriptor[] pipe=null;

    try {
      pipe=ParcelFileDescriptor.createPipe();
      AssetManager assets=getContext().getResources().getAssets();

      new TransferTask(assets.open(uri.getLastPathSegment()),
                       new AutoCloseOutputStream(pipe[1])).start();
    }
    catch (IOException e) {
      Log.e(getClass().getSimpleName(), "Exception opening pipe", e);
      throw new FileNotFoundException("Could not open pipe for: "
          + uri.toString());
    }

    return(pipe[0]);
  }

后台线程在哪里进行典型的流到流复制:

  static class TransferTask extends Thread {
    InputStream in;
    OutputStream out;

    TransferTask(InputStream in, OutputStream out) {
      this.in=in;
      this.out=out;
    }

    @Override
    public void run() {
      byte[] buf=new byte[1024];
      int len;

      try {
        while ((len=in.read(buf)) > 0) {
          out.write(buf, 0, len);
        }

        in.close();
        out.close();
      }
      catch (IOException e) {
        Log.e(getClass().getSimpleName(),
              "Exception transferring file", e);
      }
    }
  }

但是，MediaPlayer 阻塞:

10-16 13:33:13.203: E/MediaPlayer(3060): Unable to to create media player
10-16 13:33:13.203: D/MediaPlayer(3060): Couldn't open file on client side, trying server side
10-16 13:33:13.207: E/TransferTask(3060): Exception transferring file
10-16 13:33:13.207: E/TransferTask(3060): java.io.IOException: write failed: EPIPE (Broken pipe)
10-16 13:33:13.207: E/TransferTask(3060):   at libcore.io.IoBridge.write(IoBridge.java:462)
10-16 13:33:13.207: E/TransferTask(3060):   at java.io.FileOutputStream.write(FileOutputStream.java:187)
10-16 13:33:13.207: E/TransferTask(3060):   at com.commonsware.android.audiolstream.PipeProvider$TransferTask.run(PipeProvider.java:120)
10-16 13:33:13.207: E/TransferTask(3060): Caused by: libcore.io.ErrnoException: write failed: EPIPE (Broken pipe)
10-16 13:33:13.207: E/TransferTask(3060):   at libcore.io.Posix.writeBytes(Native Method)
10-16 13:33:13.207: E/TransferTask(3060):   at libcore.io.Posix.write(Posix.java:178)
10-16 13:33:13.207: E/TransferTask(3060):   at libcore.io.BlockGuardOs.write(BlockGuardOs.java:191)
10-16 13:33:13.207: E/TransferTask(3060):   at libcore.io.IoBridge.write(IoBridge.java:457)
10-16 13:33:13.207: E/TransferTask(3060):   ... 2 more
10-16 13:33:13.211: E/MediaPlayer(3060): Unable to to create media player
10-16 13:33:13.218: E/TransferTask(3060): Exception transferring file
10-16 13:33:13.218: E/TransferTask(3060): java.io.IOException: write failed: EPIPE (Broken pipe)
10-16 13:33:13.218: E/TransferTask(3060):   at libcore.io.IoBridge.write(IoBridge.java:462)
10-16 13:33:13.218: E/TransferTask(3060):   at java.io.FileOutputStream.write(FileOutputStream.java:187)
10-16 13:33:13.218: E/TransferTask(3060):   at com.commonsware.android.audiolstream.PipeProvider$TransferTask.run(PipeProvider.java:120)
10-16 13:33:13.218: E/TransferTask(3060): Caused by: libcore.io.ErrnoException: write failed: EPIPE (Broken pipe)
10-16 13:33:13.218: E/TransferTask(3060):   at libcore.io.Posix.writeBytes(Native Method)
10-16 13:33:13.218: E/TransferTask(3060):   at libcore.io.Posix.write(Posix.java:178)
10-16 13:33:13.218: E/TransferTask(3060):   at libcore.io.BlockGuardOs.write(BlockGuardOs.java:191)
10-16 13:33:13.218: E/TransferTask(3060):   at libcore.io.IoBridge.write(IoBridge.java:457)
10-16 13:33:13.218: E/TransferTask(3060):   ... 2 more

有没有人见过使用 createPipe() 向 MediaPlayer 提供媒体的工作代码？

提前致谢!

Answer 1

我不确定这是否可行。当我运行这段代码时，我看到了这个踪迹:

I/AudioSystem(30916): getting audio flinger
I/AudioSystem(30916): returning new audio session id
D/IAudioFlinger(30916): newAudioSessionId In
D/AudioFlinger(28138): nextUniqueId, current 178
D/IAudioFlinger(30916): newAudioSessionId Out, id = 178
D/MediaPlayer(30916): setDataSource(Context context, content://com.commonsware.android.audiolstream/clip.ogg, Map<String, String> headers) in
D/MediaPlayer(30916): setDataSource(FileDescriptor fd) in
E/MediaPlayerService(28138): offset error

“偏移错误”来自 AOSP 中 MediaPlayerService.cpp 中的以下行，它在管道的读取端执行 fstat():

status_t MediaPlayerService::Client::setDataSource(int fd, int64_t offset, int64_t length)
{
    struct stat sb;
    int ret = fstat(fd, &sb);

    ....

    if (offset >= sb.st_size) {
        LOGE("offset error");
        ::close(fd);
        return UNKNOWN_ERROR;
    }

并且 sb.st_size 报告为 -1(通过 Java 级别的 ParcelFileDescriptor 上的 getStatSize())。错误处理程序关闭描述符，因此不久之后出现了损坏的管道错误。

根据我的经验，MediaPlayer 有很多这样的故障。除了直接在本地文件上以及(非常错误地)用于 HTTP 流媒体之外，我从未见过它适用于任何东西。我最终移植了 FFmpeg 来解决它的众多缺陷。