av_image_alloc头文件

av_image_alloc是FFmpeg中的一个函数，用于分配一个新的图像缓冲区，并返回指向该缓冲区的指针。该函数头文件为“libavutil/imgutils.h”。

函数原型如下：

uint8_t *av_image_alloc (uint8_t *pointers[4], int linesizes[4], int width, int height, enum AVPixelFormat pix_fmt, int align);

函数参数说明：

- pointers：指向指针数组的指针。该数组包含指向图像缓冲区中每个平面的指针。如果缓冲区已经分配，则该指针数组中的指针将被重新分配。
- linesizes：指向整数数组的指针，该数组包含每个平面的行大小。如果缓冲区已经分配，则该指针数组中的值将被重新分配。
- width：图像宽度（以像素为单位）。
- height：图像高度（以像素为单位）。
- pix_fmt：图像像素格式。
- align：指定缓冲区对齐方式的整数，通常为1或32。

函数返回值为指向新分配的图像缓冲区的指针。如果分配失败，则返回NULL。

使用该函数可以方便地分配一个新的图像缓冲区，以便进行图像处理和编解码等操作。

相关问题

/root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In destructor ‘virtual usb_cam::AbstractV4LUSBCam::~AbstractV4LUSBCam()’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:235:5: error: ‘av_packet_free’ was not declared in this scope av_packet_free(&avpkt); ^~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:235:5: note: suggested alternative: ‘av_packet_ref’ av_packet_free(&avpkt); ^~~~~~~~~~~~~~ av_packet_ref /root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In static member function ‘static bool usb_cam::AbstractV4LUSBCam::init_decoder()’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:375:13: error: ‘av_packet_alloc’ was not declared in this scope avpkt = av_packet_alloc(); ^~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:375:13: note: suggested alternative: ‘av_image_alloc’ avpkt = av_packet_alloc(); ^~~~~~~~~~~~~~~ av_image_alloc /root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In static member function ‘static bool usb_cam::AbstractV4LUSBCam::decode_ffmpeg(const void*, int, usb_cam::camera_image_t*)’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:775:8: error: ‘avcodec_send_packet’ was not declared in this scope if(avcodec_send_packet(avcodec_context, avpkt) < 0) ^~~~~~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:775:8: note: suggested alternative: ‘av_append_packet’ if(avcodec_send_packet(avcodec_context, avpkt) < 0) ^~~~~~~~~~~~~~~~~~~ av_append_packet /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:788:9: error: ‘avcodec_receive_frame’ was not declared in this scope if (avcodec_receive_frame(avcodec_context, avframe_camera) < 0) ^~~~~~~~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:788:9: note: suggested alternative: ‘avcodec_free_frame’ if (avcodec_receive_frame(avcodec_context, avframe_camera) < 0) ^~~~~~~~~~~~~~~~~~~~~ avcodec_free_frame usb_cam/CMakeFiles/v4l_driver.dir/build.make:110: recipe for target 'usb_cam/CMakeFiles/v4l_driver.dir/src/camera_driver.cpp.o' failed make[2]: *** [usb_cam/CMakeFiles/v4l_driver.dir/src/camera_driver.cpp.o] Error 1 CMakeFiles/Makefile2:656: recipe for target 'usb_cam/CMakeFiles/v4l_driver.dir/all' failed make[1]: *** [usb_cam/CMakeFiles/v4l_driver.dir/all] Error 2 Makefile:140: recipe for target 'all' failed make: *** [all] Error 2 Invoking "make -j4 -l4" failed

根据您提供的错误信息，错误是因为在camera_driver.cpp文件中未找到av_packet_free、av_packet_alloc、avcodec_send_packet和avcodec_receive_frame等函数。

这些函数属于FFmpeg库。请按照以下步骤检查和解决此问题：

1. 确保已正确安装了FFmpeg库。请参考FFmpeg的官方文档或安装说明，确保已正确安装了FFmpeg库。

2. 在CMakeLists.txt文件中，确保已添加链接FFmpeg库的指令。您应该使用`target_link_libraries()`函数将FFmpeg库链接到您的项目中。在您的CMakeLists.txt文件中，找到与您的目标（例如v4l_driver）相关的`add_library()`或`add_executable()`函数，并在其下方添加以下代码：

   target_link_libraries(your_target_name avcodec avformat swscale)

将`your_target_name`替换为实际的目标名称。

3. 确保在camera_driver.cpp文件中包含了必要的头文件。在camera_driver.cpp文件的开头，添加以下代码：

   extern "C" {
   #include <libavcodec/avcodec.h>
   #include <libavformat/avformat.h>
   #include <libswscale/swscale.h>
   }

根据您的实际情况调整头文件路径。

4. 重新编译您的项目，确保现在能够正确链接和使用FFmpeg库。

如果您仍然遇到问题，请提供更多关于您的CMakeLists.txt文件和相关代码的信息，以便我们能够更好地帮助您解决问题。

/root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In destructor ‘virtual usb_cam::AbstractV4LUSBCam::~AbstractV4LUSBCam()’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:236:5: error: ‘av_packet_free’ was not declared in this scope av_packet_free(&avpkt); ^~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:236:5: note: suggested alternative: ‘av_packet_ref’ av_packet_free(&avpkt); ^~~~~~~~~~~~~~ av_packet_ref /root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In static member function ‘static bool usb_cam::AbstractV4LUSBCam::init_decoder()’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:376:13: error: ‘av_packet_alloc’ was not declared in this scope avpkt = av_packet_alloc(); ^~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:376:13: note: suggested alternative: ‘av_image_alloc’ avpkt = av_packet_alloc(); ^~~~~~~~~~~~~~~ av_image_alloc /root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In static member function ‘static bool usb_cam::AbstractV4LUSBCam::decode_ffmpeg(const void*, int, usb_cam::camera_image_t*)’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:776:8: error: ‘avcodec_send_packet’ was not declared in this scope if(avcodec_send_packet(avcodec_context, avpkt) < 0) ^~~~~~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:776:8: note: suggested alternative: ‘av_append_packet’ if(avcodec_send_packet(avcodec_context, avpkt) < 0) ^~~~~~~~~~~~~~~~~~~ av_append_packet /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:789:9: error: ‘avcodec_receive_frame’ was not declared in this scope if (avcodec_receive_frame(avcodec_context, avframe_camera) < 0) ^~~~~~~~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:789:9: note: suggested alternative: ‘avcodec_free_frame’ if (avcodec_receive_frame(avcodec_context, avframe_camera) < 0) ^~~~~~~~~~~~~~~~~~~~~ avcodec_free_frame usb_cam/CMakeFiles/v4l_driver.dir/build.make:110: recipe for target 'usb_cam/CMakeFiles/v4l_driver.dir/src/camera_driver.cpp.o' failed make[2]: *** [usb_cam/CMakeFiles/v4l_driver.dir/src/camera_driver.cpp.o] Error 1 CMakeFiles/Makefile2:656: recipe for target 'usb_cam/CMakeFiles/v4l_driver.dir/all' failed make[1]: *** [usb_cam/CMakeFiles/v4l_driver.dir/all] Error 2 Makefile:140: recipe for target 'all' failed make: *** [all] Error 2 Invoking "make -j4 -l4" failed

根据错误信息，您的代码在以下几个地方使用了未声明的 FFmpeg 函数：

- av_packet_free()
- av_packet_alloc()
- avcodec_send_packet()
- avcodec_receive_frame()

这些错误提示表明您可能没有正确包含 FFmpeg 相关的头文件。请确保在 camera_driver.cpp 文件中包含正确的头文件。您可以尝试添加以下代码段到 camera_driver.cpp 文件的开头：

extern "C" {
#include <libavcodec/avcodec.h>
}

这将确保正确声明和包含 FFmpeg 的 avcodec 头文件。请确保将此代码段添加到其他头文件的上方。

另外，请确保已经正确安装了 FFmpeg 库，并且在 CMakeLists.txt 文件中添加了正确的链接库指令。您可以使用类似以下的代码将 FFmpeg 的库链接到您的目标上：

target_link_libraries(your_target_name avcodec avformat swscale)

请注意将 `your_target_name` 替换为您实际的目标名称。

如果问题仍然存在，请检查您的环境是否正确配置了 FFmpeg，并且确保您正在使用正确版本的 FFmpeg 库。

如果您还有其他问题，请随时提问。