简介

MediaExtractor的作用是负责将指定类型的媒体文件从文件中找到轨道，并填充到MediaCodec的缓冲区中，内部方法均为native方法，可以把音频和视频的数据进行分离。

正文

API介绍：

• setDataSource(String path)：即可以设置本地文件又可以设置网络文件
• getTrackCount()：得到源文件通道数
• getTrackFormat(int index)：获取指定（index）的通道格式
• getSampleTime()：返回当前的时间戳
• readSampleData(ByteBuffer byteBuf, int offset)：把指定通道中的数据按偏移量读取到ByteBuffer中
• advance()：读取下一帧数据
• release(): 读取结束后释放资源

使用方法：

...
    extractor = new MediaExtractor();
            try {
                extractor.setDataSource(SAMPLE);
            } catch (IOException e) {
                e.printStackTrace();
            }

            for (int i = 0; i < extractor.getTrackCount(); i++) {
                MediaFormat format = extractor.getTrackFormat(i);
                String mime = format.getString(MediaFormat.KEY_MIME);
                if (mime.startsWith("video/")) {
                    extractor.selectTrack(i);
                    try {
                        decoder = MediaCodec.createDecoderByType(mime);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    decoder.configure(format, surface, null, 0);
                    break;
                }
            }

            if (decoder == null) {
                Log.e("DecodeActivity", "Can't find video info!");
                return;
            }

            decoder.start();

            ByteBuffer[] inputBuffers = decoder.getInputBuffers();
            ByteBuffer[] outputBuffers = decoder.getOutputBuffers();
            MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();
            boolean isEOS = false;
            long startMs = System.currentTimeMillis();

            while (!Thread.interrupted()) {
                if (!isEOS) {
                    int inIndex = decoder.dequeueInputBuffer(10000);
                    if (inIndex >= 0) {
                        ByteBuffer buffer = inputBuffers[inIndex];
                        int sampleSize = extractor.readSampleData(buffer, 0);
                        if (sampleSize < 0) {
                            // We shouldn't stop the playback at this point, just pass the EOS
                            // flag to decoder, we will get it again from the
                            // dequeueOutputBuffer
                            Log.d("DecodeActivity", "InputBuffer BUFFER_FLAG_END_OF_STREAM");
                            decoder.queueInputBuffer(inIndex, 0, 0, 0, MediaCodec.BUFFER_FLAG_END_OF_STREAM);
                            isEOS = true;
                        } else {
                            decoder.queueInputBuffer(inIndex, 0, sampleSize, extractor.getSampleTime(), 0);
                            extractor.advance();
                        }
                    }
                }

                int outIndex = decoder.dequeueOutputBuffer(info, 10000);
                switch (outIndex) {
                    case MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED:
                        Log.d("DecodeActivity", "INFO_OUTPUT_BUFFERS_CHANGED");
                        outputBuffers = decoder.getOutputBuffers();
                        break;
                    case MediaCodec.INFO_OUTPUT_FORMAT_CHANGED:
                        Log.d("DecodeActivity", "New format " + decoder.getOutputFormat());
                        break;
                    case MediaCodec.INFO_TRY_AGAIN_LATER:
                        Log.d("DecodeActivity", "dequeueOutputBuffer timed out!");
                        break;
                    default:
                        ByteBuffer buffer = outputBuffers[outIndex];
                        Log.v("DecodeActivity", "We can't use this buffer but render it due to the API limit, " + buffer);

                        // We use a very simple clock to keep the video FPS, or the video
                        // playback will be too fast
                        while (info.presentationTimeUs / 1000 > System.currentTimeMillis() - startMs) {
                            try {
                                sleep(10);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                                break;
                            }
                        }
                        decoder.releaseOutputBuffer(outIndex, true);
                        break;
                }

                // All decoded frames have been rendered, we can stop playing now
                if ((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
                    Log.d("DecodeActivity", "OutputBuffer BUFFER_FLAG_END_OF_STREAM");
                    break;
                }
            }

            decoder.stop();
            decoder.release();
            extractor.release();
...

总结

通过MediaExtractor将媒体文件分解音频和视频数据，并传递给MediaCodec进行解码。