Playing a video from memory

问题

Is it possible to play a video directly from memory, using the MemoryFile class? I tried:

AssetFileDescriptor afd = getResources().openRawResourceFd(videoResId);
InputStream is = getResources().openRawResource(videoResId);
// BufferedReader br = new BufferedReader(new InputStreamReader(is));
try {
    memoryFile = new MemoryFile("myvideo", (int) afd.getDeclaredLength());
    byte[] buffer = new byte[8192];
    int bytesRead, totalBytesRead = 0;
    while ((bytesRead = is.read(buffer)) != -1) {
        memoryFile.writeBytes(buffer, 0, 0, bytesRead);
        totalBytesRead += bytesRead;
    }
    is.close();
} catch (IOException e) {
    e.printStackTrace();
}
FileDescriptor mfd = MemoryFileUtil.getFileDescriptor(memoryFile);

videoPlayer = new MediaPlayer();
try {
    // videoPlayer.setDataSource(afd.getFileDescriptor(), afd.getStartOffset(), afd.getLength());
    videoPlayer.setDataSource(mfd, 0, afd.getLength());
    videoPlayer.prepare();
} catch (Throwable e) {
    e.printStackTrace();
}
videoPlayer.setLooping(true);
_setPlayerSurface(videoPlayer, holder);

where the MemoryFileUtil class is from https://code.google.com/p/sunnykwong/source/browse/trunk/One+More+Clock/src/com/sunnykwong/omc/MemoryFileUtil.java?spec=svn699&r=699

However the surface remains black. If however I call setDataSource() with the afd AssetFileDescriptor (the commented line above) it works perfectly.

Am I doing something wrong with the MemoryFile? Is there some pointer I need to reset on it?

回答1:

I doubt MemoryFile can be made to work. After digging into the MediaPlayer#setDataSource code I eventually found the native source

status_t MediaPlayerService::Client::setDataSource(int fd, int64_t offset, int64_t length)
{
    ALOGV("setDataSource fd=%d, offset=%lld, length=%lld", fd, offset, length);
    struct stat sb;
    int ret = fstat(fd, &sb);
    if (ret != 0) {
        ALOGE("fstat(%d) failed: %d, %s", fd, ret, strerror(errno));
        return UNKNOWN_ERROR;
    }

    ALOGV("st_dev  = %llu", sb.st_dev);
    ALOGV("st_mode = %u", sb.st_mode);
    ALOGV("st_uid  = %lu", sb.st_uid);
    ALOGV("st_gid  = %lu", sb.st_gid);
    ALOGV("st_size = %llu", sb.st_size);

    if (offset >= sb.st_size) {
        ALOGE("offset error");
        ::close(fd);
        return UNKNOWN_ERROR;
    }
    if (offset + length > sb.st_size) {
        length = sb.st_size - offset;
        ALOGV("calculated length = %lld", length);
    }
    // ...

Internally it fstat's the file descriptor you pass it. My suspicion is that this call either fails outright or it's returning the wrong size, e.g. 0.

来源：https://stackoverflow.com/questions/22686367/playing-a-video-from-memory