安卓录制视频的时候，预览和录制设置成不同分辨率的步骤

项目中使用全屏预览，但是录制文件的大小需要限制，所以不能把全屏的分辨率直接录制下来，我在网上看到的问答摘录下来，原地址：http://stackoverflow.com/questions/14132558/record-video-with-a-different-preview-size-than-the-resulting-video-file

问题：

I am attempting to allow users to record video that is a different size than the actual on-screen preview that they can see while recording. This seems to be possible from this documentation concerning the getSupportedVideoSizes function which states:

If the returned list is not null, the returned list will contain at least one Size and one of the sizes in the returned list must be passed to MediaRecorder.setVideoSize() for camcorder application if camera is used as the video source. In this case, the size of the preview can be different from the resolution of the recorded video during video recording.

This suggests that some phones will return null from this fn (in my experience the Galaxy SIII does) but for those who do not, it is possible to provide a preview with a different resolution than the actual video. Is this understanding correct? Do some phones allow the behavior and others not?

Attempting a Solution:

In the official description of the setPreviewDisplay function, which is used in the lengthy process of setting up for video recording, it is mentioned that:

If this method is called with null surface or not called at all, media recorder will not change the preview surface of the camera.

This seems to be what I want, but unfortunately if I do this, the whole video recording process is completely messed up. I am assuming that this function can not be passed null or not called at all in the process of recording video. Perhaps in other contexts this is okay. Unfortunately though, this does not seem to help me.

My only next steps are to look into TextureViews and to use a preview Texture as opposed to a typical SurfaceView implementation in order to use openGL to stretch the texture to my desired size that differs from the actual resolution (and crop any excess off the screen), and then to Construct a Surface for the setPreviewDisplay function with the Surface(SurfaceTexture surfaceTexture) constructor for a Surface. I would like to avoid using a TextureView due to incompatibility below ICS, and also because this adds significant complexity.

This seems like a delicate process, but I am hoping someone can offer some advice in this area.

Thank you.

解答

As you mention, this is only possible when getSupportedVideoSizes() returns a non-null list.

But if you do see a non-null list, then this simple approach should work:

1. Set the desired preview resolution with setPreviewSize; the size you select has to be one of the sizes given from getSupportedPreviewSizes.

2. Set the preview display to your SurfaceView or SurfaceTexture with setPreviewDisplay or setPreviewTexture, respectively.

3. Start preview.

4. Create the media recorder, and set its video size either directly with setVideoSize using one of the sizes from getSupportedVideoSizes, or use one of the predefined Camcorder profiles to configure all the media recorder settings for a given quality/size.

5. Pass the camera object to MediaRecorder's setCamera call, configure the rest of the media recorder, and start recording.

On devices with a non-null getSupportedVideoSizes list, this should result in preview staying at the resolution set by your setPreviewSize call, with recording operating at the set video size/camcorder profile resolution. On devices with no supported video sizes, the preview size will be reset by the MediaRecorder to match the recording size. You should be able to test this by setting a very low preview resolution and a high recording resolution (say, 160x120 for preview, 720p for recording). It should be obvious if the MediaRecorder switches the preview resolution to 720p when recording starts, as the preview quality will jump substantially.

Note that the preview size is not directly linked to the dimensions of the display SurfaceView; the output of the camera preview will be scaled to fit into the SurfaceView, so if your SurfaceView's dimensions are, say 100x100 pixels due to your layout and device, whatever the preview resolution you use will be scaled to 100x100 for display. So you still need to make sure to keep the SurfaceView's aspect ratio correct so that the preview is not distorted.

And for power efficiency, you should not use a preview resolution much higher than the actual number of pixels in your SurfaceView, since the additional resolution will be lost in fitting the preview in the surfaceview. This is of course only possible for recording when getSupportedVideoSizes() returns a non-null value.

关键是他列的步骤1，2，3，4，5 按照步骤做可以实现