Android之MediaCodec视频解码

简介

MediaCodec:负责媒体文件的编码和解码工作，内部方法均为native方法。

正文

视频播放主要步骤如下：

• 将资源加载到MediaExtractor
• 获取视频所在轨道
• 设置MediaExtractor选中视频所在轨道
• 创建视频解码的MediaCodec
• 循环开始
• 将extractor中资源以一个单位填充到decorder的输入缓存区中
• decorder之后，将解码的视频填充到输出缓冲区中
• 将缓冲区中的数据渲染到surface中
• 循环结束，直至视频资源的末尾
• 释放资源

视频播放创建一个播放的Thread

private class PlayerThread extends Thread {
    ...
}

1. 初始化

   private MediaExtractor extractor;
   private MediaCodec decoder;
   extractor = new MediaExtractor();
   ByteBuffer[] inputBuffers = decoder.getInputBuffers();
   ByteBuffer[] outputBuffers = decoder.getOutputBuffers();
   MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();

2.将资源加载到MediaExtractor

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

3.获取视频所在轨道,设置MediaExtractor选中视频所在轨道,创建视频解码的MediaCodec

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;
                }
            }

4.循环操作：将extractor中资源以一个单位填充到decorder的输入缓存区中,decorder之后，将解码的视频填充到输出缓冲区中,将缓冲区中的数据渲染到surface中,循环结束，直至视频资源的末尾

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;
                            }
                        }
                        //将缓冲区中数据渲染到surface,render=true就会渲染到surface
                        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;
                }
            }

5.释放资源

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

总结

了解mediacodec和MediaExtractor的api和原理，按视频播放的步骤进行解码播放。

学习一步一个脚印，谢谢今天的自己。