如何使用 Libav 在 Windows 上捕获相机设备？

发布于 2024-12-06 03:16:06 字数 1309 浏览 0 评论 0原文

有没有办法使用 Libav 在 Windows 平台上从与 DirectShow 一样多的相机类型捕获帧？我需要在不使用 DirectShow 滤镜的情况下捕获相机输出，并且希望我的应用程序能够与多种相机设备类型配合使用。

我在互联网上搜索了 libav 的此功能，发现可以通过 libav 使用特殊输入格式“vfwcap”来完成。类似的东西（不确定代码的正确性 - 我自己写的）：

AVFormatParameters formatParams = NULL;
AVInputFormat* pInfmt = NULL;
pInFormatCtx*  pInFormatCtx = NULL;

av_register_all();

//formatParams.device = NULL; //this was probably deprecated and then removed
formatParams.channel = 0;
formatParams.standard = "ntsc"; //deprecated too but still available
formatParams.width = 640;
formatParams.height = 480;
formatParams.time_base.num = 1000;
formatParams.time_base.den = 30000; //so we want 30000/1000 = 30 frames per second
formatParams.prealloced_context = 0;


pInfmt = av_find_input_format("vfwcap");
if( !pInfmt )
{
  fprintf(stderr,"Unknown input format\n");
  return -1;
}

// Open video file (formatParams can be NULL for autodetecting probably)
if (av_open_input_file(&pInFormatCtx, 0, pInfmt, 0, formatParams) < 0)
   return -1; // Couldn't open device

/* Same as video4linux code*/

所以另一个问题是：Libav 支持多少设备？我所发现的有关 Windows 上使用 libav 捕获相机输出的所有内容都是建议使用 DirectShow 来实现此目的，因为 libav 支持的设备太少。也许情况现在已经改变了，它确实支持足够的设备来在生产应用程序中使用它？

如果这是不可能的.. 好吧，我希望我的问题不会毫无用处，这个由不同来源的代码组成的代码将帮助对此主题感兴趣的人，因为整个互联网上关于它的信息确实太少了。

原文

Is there any way to capture frames from as many camera types as DirectShow do on Windows platform using Libav? I need to capture a camera output without using DirectShow filters and I want my application to work with many camera devices types.

I have searched the Internet about this capability of libav and found that it can be done via libav using special input format "vfwcap". Something like that (don't sure about code correctness - I wrote it by myself):

AVFormatParameters formatParams = NULL;
AVInputFormat* pInfmt = NULL;
pInFormatCtx*  pInFormatCtx = NULL;

av_register_all();

//formatParams.device = NULL; //this was probably deprecated and then removed
formatParams.channel = 0;
formatParams.standard = "ntsc"; //deprecated too but still available
formatParams.width = 640;
formatParams.height = 480;
formatParams.time_base.num = 1000;
formatParams.time_base.den = 30000; //so we want 30000/1000 = 30 frames per second
formatParams.prealloced_context = 0;


pInfmt = av_find_input_format("vfwcap");
if( !pInfmt )
{
  fprintf(stderr,"Unknown input format\n");
  return -1;
}

// Open video file (formatParams can be NULL for autodetecting probably)
if (av_open_input_file(&pInFormatCtx, 0, pInfmt, 0, formatParams) < 0)
   return -1; // Couldn't open device

/* Same as video4linux code*/

So another question is: how many devices are supported by Libav? All I have found about capture cameras output with libav on windows is advice to use DirectShow for this purpose because libav supports too few devices. Maybe situation has already changed now and it does support enough devices to use it in production applications?

If this isn't possible.. Well I hope my question won't be useless and this composed from different sources piece of code will help someone interested in this theme 'coz there are really too few information about it in the whole internet.

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