如何使用 MediaCodec 从视频中获取位图（帧）

Question

我正在尝试使用 MediaCodec 从视频文件中获取所有帧。如果我尝试在 SurfaceView 上显示视频，一切正常。但是如果表面为空，当我尝试从字节数组中获取位图时，总是会得到空或运行时异常。

这是我的代码：

private class PlayerThread extends Thread {
    private MediaExtractor extractor;
    private MediaCodec decoder;
    private Surface surface;

    public PlayerThread(Surface surface) {
        this.surface = surface;
    }

    @Override
    public void run() {
        extractor = new MediaExtractor();
        extractor.setDataSource(videoPath);

        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);
                decoder = MediaCodec.createDecoderByType(mime);
                decoder.configure(format, /*surface*/ null, 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();
        BufferInfo info = new BufferInfo();
        boolean isEOS = false;

        while (!Thread.interrupted()) {
            ++numFrames;
            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:
                // I tried get Bitmap on few ways
                //1.
                //ByteBuffer buffer = outputBuffers[outIndex];
                //byte[] ba = new byte[buffer.remaining()];
                //buffer.get(ba);
                //final Bitmap bmp = BitmapFactory.decodeByteArray(ba, 0, ba.length);// this return null
                //2. 
                //ByteBuffer buffer = outputBuffers[outIndex];
                //final Bitmap bmp = Bitmap.createBitmap(1920, 1080, Config.ARGB_8888);//using MediaFormat object I know width and height
                //int a = bmp.getByteCount(); //8294400
                //buffer.rewind();
                //int b = buffer.capacity();//3137536
                //int c = buffer.remaining();//3137536
                //bmp.copyPixelsFromBuffer(buffer); // java.lang.RuntimeException: Buffer not large enough for pixels
                //I know what exception mean, but i don't know why xception occurs

                //In this place I need bitmap

                // 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();
    }
}

我不知道如何解决它。

萨摩斯

Answer 1

您的代码（或者，可以说是 MediaCodec）存在一些问题。

首先，MediaCodec 中的 ByteBuffer 处理很差，因此您必须根据 dequeueOutputBuffer() 填写的 BufferInfo 对象中的值手动设置缓冲区参数。

其次，来自 MediaCodec 的值是 YUV 格式，而不是 RGB。从 Android 4.4 开始，Android 框架不提供将输出转换为位图的功能。您需要提供自己的 YUV 到 RGB 转换器（复数 - 有多种格式）。一些设备使用专有的、未记录的颜色格式。

您可以在 CTS EncodeDecodeTest buffer-to-buffer 方法（例如 checkFrame()）中查看提取和检查 MediaCodec 解码器缓冲区内容的示例。

解决此问题的更可靠方法是返回解码到 Surface，但使用 OpenGL ES 提取像素。 bigflake ExtractMpegFramesTest 展示了如何做到这一点。

Answer 2

简短的回答是：

在你的 switch 语句的默认部分，你需要重置 ByteBuffer 的位置，所以不是：

ByteBuffer buffer = outputBuffers[outIndex];
byte[] ba = new byte[buffer.remaining()];
buffer.get(ba); 

你应该有类似的东西

ByteBuffer buffer = outputBuffers[outIndex];
buffer.position(info.offset);
buffer.limit(info.offset + info.size);
byte[] ba = new byte[buffer.remaining()];
buffer.get(ba); 

在您的原始代码中，您会发现您的 ByteBuffer 的剩余（）为 0。