av_packet_ref（） 函数含义

av_packet_ref() 函数的含义是将一个 AVPacket 对象的引用计数增加 1，并将一个新的 AVPacket 对象与原始 AVPacket 共享同一数据缓冲区。这个函数通常用于在多个线程或函数之间传递 AVPacket 对象时确保数据缓冲区的安全性。在完成使用后，应该调用 av_packet_unref() 函数将引用计数减少 1，并在引用计数为 0 时释放数据缓冲区。

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。