MediaCodec和Camera：颜色空间不匹配 [英] MediaCodec and Camera: colorspaces don't match

问题描述

我一直在尝试使用H264编码来处理由Android平板电脑上的相机捕获的输入，使用新的低级 MediaCodec 。我遇到了一些困难，因为MediaCodecAPI的记录不好，但我已经得到了一些工作，最后。

我把相机设置为如下：

  Camera.Parameters parameters = mCamera.getParameters 
 parameter.setPreviewFormat（ImageFormat.YV12）; //< 1> 
 parameter.setPreviewFpsRange（4000,60000）; 
 parameter.setPreviewSize（640，480）; 
 mCamera.setParameters（parameters）; 
 

对于编码部分，我实例化MediaCodec对象如下：

  mediaCodec = MediaCodec.createEncoderByType（video / avc）; 
 MediaFormat mediaFormat = MediaFormat.createVideoFormat（video / avc，640，480）; 
 mediaFormat.setInteger（MediaFormat.KEY_BIT_RATE，500000）; 
 mediaFormat.setInteger（MediaFormat.KEY_FRAME_RATE，15）; 
 mediaFormat.setInteger（MediaFormat.KEY_COLOR_FORMAT，
 MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420Planar）; //< 2> 
 mediaFormat.setInteger（MediaFormat.KEY_I_FRAME_INTERVAL，5）; 
 mediaCodec.configure（mediaFormat，null，null，MediaCodec.CONFIGURE_FLAG_ENCODE）; 
 mediaCodec.start（）; 
  

最终的目标是创建一个RTP流（对应于Skype）我只是将原始H264直接流到我的桌面。在这里我使用以下GStreamer-pipeline显示结果：

  gst-launch udpsrc port = 5555！ video / x-h264，width = 640，height = 480，framerate = 15/1！ ffdec_h264！ autovideosink 
  

所有效果都很好，除了颜色。我需要在计算机中设置2个颜色格式：一个用于相机预览（标记为< 1> 的行），一个用于MediaCodec对象c $ c>< 2> ）

要确定< 1& / code>我使用 parameters.getSupportedPreviewFormats（）。从这里，我知道相机上唯一支持的格式是 ImageFormat。 NV21 和 ImageFormat.YV2 。 p>



对于< 2> ，我检索了 MediaCodecInfo.CodecCapabilities - 类型为 video / avc 的对象，为整数值19（对应< a href =http://developer.android.com/reference/android/media/MediaCodecInfo.CodecCapabilities.html#COLOR_FormatYUV420Planar =nofollow noreferrer> MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420Planar 和2130708361（其中' t对应于 MediaCodecInfo.CodecCapabilities 的任何值。

任何其他值都会导致崩溃。

组合这些设置会产生不同的结果，将在下面显示。这里是Android上的屏幕截图（即真正的颜色）：

以下是Gstreamer显示的结果：

< 1> = NV21，< 2> = COLOR_FormatYUV420Planar

< 1> = NV21，< code> = 2130708361


< 1> = YV2，< 2> = COLOR_FormatYUV420Planar

< 1> = YV2，< 2> = 2130708361

可以看出，满意。 YV2色彩空间看起来最有前途，但它看起来像红色（Cr）和蓝色（Cb）是颠倒的。 NV21看起来是隔行扫描的（但我不是这方面的专家）。

由于目的是为了与Skype沟通，我认为我不应该改变解码器（即Gstreamer命令），对吧？这是要在Android中解决，如果是这样：如何？或者可以通过添加某些RTP有效载荷信息来解决？任何其他建议？

解决方案

我通过使用一个简单的函数在Android级别交换byteplanes来解决它：

  public byte [] swapYV12toI420（byte [] yv12bytes，int width，int height）{
 byte [] i420bytes = new byte [ yv12bytes.length]; 
 for（int i = 0; i  i420bytes [i] = yv12bytes [i] 
 for（int i = width * height; i  i420bytes [i] = yv12bytes [i + height / 2）]; 
 for（int i = width * height +（width / 2 * height / 2）; i  i420bytes [ i] = yv12bytes [i-（width / 2 * height / 2）]; 
 return i420bytes; 
} 
  

I have been trying to get H264 encoding to work with input captured by the camera on an Android tablet using the new low-level MediaCodec. I have gone through some difficulties with this, since the MediaCodecAPI is poorly documented, but I've gotten something to work at last.

I'm setting up the camera as follows:

        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setPreviewFormat(ImageFormat.YV12); // <1>
        parameters.setPreviewFpsRange(4000,60000);
        parameters.setPreviewSize(640, 480);            
        mCamera.setParameters(parameters);

For the encoding part, I'm instantiating the MediaCodec object as follows:

    mediaCodec = MediaCodec.createEncoderByType("video/avc");
    MediaFormat mediaFormat = MediaFormat.createVideoFormat("video/avc", 640, 480);
    mediaFormat.setInteger(MediaFormat.KEY_BIT_RATE, 500000);
    mediaFormat.setInteger(MediaFormat.KEY_FRAME_RATE, 15);
    mediaFormat.setInteger(MediaFormat.KEY_COLOR_FORMAT,
            MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420Planar); // <2>
    mediaFormat.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, 5);
    mediaCodec.configure(mediaFormat, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
    mediaCodec.start();

The final goal is to create an RTP-stream (and correspond with Skype), but so far I am only streaming the raw H264 directly to my desktop. There I use the following GStreamer-pipeline to show the result:

gst-launch udpsrc port=5555 ! video/x-h264,width=640,height=480,framerate=15/1 ! ffdec_h264 ! autovideosink

All works well, except for the colors. I need to set 2 colorformats in the computer: one for the camera-preview (line tagged with <1>) and one for the MediaCodec-object (tagged with <2>)

To determine the acceptable values for the lines <1> I used parameters.getSupportedPreviewFormats(). From this, I know that the only supported formats on the camera are ImageFormat.NV21 and ImageFormat.YV2.

For <2>, I retrieved the MediaCodecInfo.CodecCapabilities-object for type video/avc, being the integer values 19 (corresponding with MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420Planar and 2130708361 (which doesn't correspond with any value of MediaCodecInfo.CodecCapabilities).

Any other value than the above results in a crash.

Combining these settings gives different results, which I'll show below. Here's the screenshot on Android (i.e. the "real" colors): Here are the results as shown by Gstreamer:

<1> = NV21, <2> = COLOR_FormatYUV420Planar

<1> = NV21, <2> = 2130708361

<1> = YV2, <2> = COLOR_FormatYUV420Planar

<1> = YV2, <2> = 2130708361

As can be seen, none of these are satisfying. The YV2-colorspace looks the most promising, but it looks like red (Cr) and blue (Cb) are inverted. The NV21 looks interlaced I guess (however, I'm no expert in this field).

Since the purpose is to communicate with Skype, I assume I shouldn't change the decoder (i.e. the Gstreamer-command), right? Is this to be solved in Android and if so: how? Or can this be solved by adding certain RTP payload information? Any other suggestion?

解决方案

I solved it by swapping the byteplanes myself on Android level, using a simple function:

public byte[] swapYV12toI420(byte[] yv12bytes, int width, int height) {
    byte[] i420bytes = new byte[yv12bytes.length];
    for (int i = 0; i < width*height; i++)
        i420bytes[i] = yv12bytes[i];
    for (int i = width*height; i < width*height + (width/2*height/2); i++)
        i420bytes[i] = yv12bytes[i + (width/2*height/2)];
    for (int i = width*height + (width/2*height/2); i < width*height + 2*(width/2*height/2); i++)
        i420bytes[i] = yv12bytes[i - (width/2*height/2)];
    return i420bytes;
}

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