Question

我正在使用AVFoundation使用AVCaptureMovieFileOutput从设备的相机录制到电影文件。我希望允许用户在录制开始之前在高帧率和高分辨率模式之间切换，但我无法弄清楚你应该知道哪个AVCaptureDeviceFormat产生适合视频录制的最高分辨率。 / p>

例如，在我正在测试的iPod touch上，它列出了后置摄像头的以下设备格式：

<AVCaptureDeviceFormat: 0x13108e260 'vide'/'420v'  192x 144, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @17.00), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310911a0 'vide'/'420f'  192x 144, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @17.00), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310afa60 'vide'/'420v'  352x 288, { 2- 30 fps}, HRSI:2992x2448, fov:49.745, max zoom:153.00 (upscales @8.50), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310af9b0 'vide'/'420f'  352x 288, { 2- 30 fps}, HRSI:2992x2448, fov:49.745, max zoom:153.00 (upscales @8.50), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x131092ad0 'vide'/'420v'  480x 360, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @6.80), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x13108f1c0 'vide'/'420f'  480x 360, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @6.80), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310af300 'vide'/'420v'  640x 480, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @5.10), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x131021990 'vide'/'420f'  640x 480, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @5.10), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310ac0f0 'vide'/'420v'  960x 540, { 2- 30 fps}, HRSI:3264x1836, fov:54.267, supports vis, max zoom:104.38 (upscales @3.09), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310ac180 'vide'/'420f'  960x 540, { 2- 30 fps}, HRSI:3264x1836, fov:54.267, supports vis, max zoom:104.38 (upscales @3.09), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x131091550 'vide'/'420v' 1280x 720, { 2- 30 fps}, HRSI:3264x1836, fov:54.267, supports vis, max zoom:95.62 (upscales @2.32), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310ab800 'vide'/'420f' 1280x 720, { 2- 30 fps}, HRSI:3264x1836, fov:54.267, supports vis, max zoom:95.62 (upscales @2.32), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x13100a350 'vide'/'420v' 1280x 720, { 3-120 fps}, fov:54.267, binned, supports vis, max zoom:52.12 (upscales @1.16), AF System:1, ISO:24.0-768.0, SS:0.000025-0.333333>
<AVCaptureDeviceFormat: 0x131090270 'vide'/'420f' 1280x 720, { 3-120 fps}, fov:54.267, binned, supports vis, max zoom:52.12 (upscales @1.16), AF System:1, ISO:24.0-768.0, SS:0.000025-0.333333>
<AVCaptureDeviceFormat: 0x131021510 'vide'/'420v' 1920x1080, { 2- 30 fps}, HRSI:3264x1836, fov:54.267, supports vis, max zoom:95.62 (upscales @1.55), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x1310a2130 'vide'/'420f' 1920x1080, { 2- 30 fps}, HRSI:3264x1836, fov:54.267, supports vis, max zoom:95.62 (upscales @1.55), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x12fe17b90 'vide'/'420v' 2592x1936, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @1.26), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x13108e010 'vide'/'420f' 2592x1936, { 2- 30 fps}, HRSI:3264x2448, fov:54.267, max zoom:153.00 (upscales @1.26), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x12fe17be0 'vide'/'420v' 3264x2448, { 2- 30 fps}, fov:54.267, max zoom:153.00 (upscales @1.00), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>
<AVCaptureDeviceFormat: 0x12fe17c40 'vide'/'420f' 3264x2448, { 2- 30 fps}, fov:54.267, max zoom:153.00 (upscales @1.00), AF System:1, ISO:24.0-768.0, SS:0.000024-0.500000>

选择最高帧速率相当简单（文档中给出了一个示例）;您只需要遍历格式及其支持的帧速率范围，即可找到帧率最高的帧速率。据我所知，具有最高帧速率的格式始终可用于录制到视频文件。

当我尝试找到分辨率最高的格式时，会出现问题。在这种情况下，1080p是您可以录制的最高音，但格式一直列在2448p之间;我可以将相机硬件切换为这种格式，但它拒绝录制到任何高于1080p的文件。当然我可以硬编码只使用1080p，但我们现在有支持4K录制的设备。

我的问题是，如何过滤此列表，使其仅显示适合录制的格式？我查看了AVCaptureDeviceFormat和CMFormatDescription的文档，但找不到任何指示给定格式是否可记录的内容。我已经看到this question类似，但在格式之间不断切换，直到isActive为真，这似乎是一种糟糕的做法。

我是否可以找到正确的格式而无需全部查看哪些格式有效？

Answer 1

在大多数情况下，将AVCaptureSession.sessionPreset设置为AVCaptureSessionPreset...之一就足够了。使用canSetSessionPreset(preset:)检查当前设备是否支持预设。

我想获得最高分辨率（宽度）;无论帧速率如何等等。这是我的解决方案：

captureSession.sessionPreset = AVCaptureSessionPresetInputPriority // Required for the "activeFormat" of the device to be used
let highresFormat = (device.formats as! [AVCaptureDeviceFormat])
    .filter { CMFormatDescriptionGetMediaSubType($0.formatDescription) == 875704422 } // Full range 420f
    .maxElement { a, b in CMVideoFormatDescriptionGetDimensions(a.formatDescription).width < CMVideoFormatDescriptionGetDimensions(b.formatDescription).width }
if let format = highresFormat {
    device.activeFormat = format
}

不可否认，获得“420 f ”（而不是“420 v ”）变体有点奇怪......

由于每个设备都返回AVCaptureDevice.formats的不同格式，我认为任何返回的格式都适用于当前设备。有些信息可以在Apple的technical note中找到。

如何找到适合录制到文件的最高分辨率AVCaptureDeviceFormat？

1 个答案: