上一篇文章讲使用ffmpeg函数接口去获取本地摄像头信息，这种方式只能从ffmpeg5版本开始才具备，那ffmpeg3/4只能干瞪眼？那肯定不行的，必须要想办法打通这个功能，查阅信息发现可以执行命令 ffmpeg -f dshow -list_devices true -i dummy 去获取，会通过日志打印出来，这是一个非常好的苗头，起码验证ffmpeg的里面肯定还有其他方式可以执行成功，于是抓住这个机会，研究如何从日志中获取数据，发型可以通过av_log_set_callback设置日志回调函数，然后所有的日志打印会在该函数中全部拿到，拿到后过滤不需要的信息就行，使用完成以后，通过av_log_set_callback(av_log_default_callback);重新设置日志回调以便恢复原样即可。
二、效果图
五、相关代码 #include "ffmpegdevice.h"#include "widgethead.h"QString FFmpegDevice::logType = QString();QString FFmpegDevice::logFlag = QString();QStringList FFmpegDevice::logResult = QStringList();void FFmpegDevice::logCallback(void *ptr, int level, const char *fmt, va_list vl){ static QMutex mutex; QMutexLocker locker(&mutex); char buf[1024]; vsprintf(buf, fmt, vl); QString line = buf; line = line.trimmed(); line.replace("\r", ""); line.replace("\n", ""); line.replace("\"", ""); //qDebug() << TIMEMS << line; //根据不同的类型解析不同的结果 if (FFmpegDevice::logType == "list_devices") { FFmpegDevice::log_list_devices(line); } else if (FFmpegDevice::logType == "list_options") { FFmpegDevice::log_list_options(line); }}void FFmpegDevice::log_list_devices(const QString &line){#if (FFMPEG_VERSION_MAJOR < 5) //搞个标记记录接下来是什么结果 if (line.startsWith("DirectShow video devices")) { FFmpegDevice::logFlag = "video"; } else if (line.startsWith("DirectShow audio devices")) { FFmpegDevice::logFlag = "audio"; } //过滤一些不需要的结果 if (line.startsWith("DirectShow") || line.startsWith("Alternative")) { return; } QString result = QString("%1|%2").arg(FFmpegDevice::logFlag).arg(line); if (!FFmpegDevice::logResult.contains(result)) { FFmpegDevice::logResult << result; }#else if (line.startsWith("(video") || line.startsWith("(audio")) { QString type = line.mid(1, line.length()); QString result = QString("%1|%2").arg(type).arg(FFmpegDevice::logFlag); if (!FFmpegDevice::logResult.contains(result)) { FFmpegDevice::logResult << result; } } else { FFmpegDevice::logFlag = line; }#endif}void FFmpegDevice::log_list_options(const QString &line){ //搞个标记记录接下来是什么结果 if (line.startsWith("vcodec=") || line.startsWith("pixel_format=")) { FFmpegDevice::logFlag = line; } if (line.startsWith("min s=") && !FFmpegDevice::logFlag.isEmpty()) { QString result = QString("%1 %2").arg(FFmpegDevice::logFlag).arg(line); if (!FFmpegDevice::logResult.contains(result)) { FFmpegDevice::logResult << result; } } //音频设备参数 if (line.contains("ch=")) { FFmpegDevice::logResult << line; }}void FFmpegDevice::getInputDevices(bool video, QStringList &devices){ QStringList names; //ffmpeg5以上版本可以直接通过函数获取#if (FFMPEG_VERSION_MAJOR < 5) QStringList infos = FFmpegDevice::getInputDevices(video ? Device_Video : Device_Audio); foreach (QString info, infos) { QString name = info.split("|").last(); if (video && info.startsWith("video")) { names << name; } else if (!video && info.startsWith("audio")) { names << name; } }#else#ifdef ffmpegdevice names << FFmpegDevice::getInputDevices(video);#endif#endif //去重复加入到集合 //qDebug() << video << names; foreach (QString name, names) { if (!devices.contains(name)) { devices << name; } }}//安装工具命令 sudo apt-get install v4l-utils//获取所有设备 v4l2-ctl --list-devices//获取所有格式 v4l2-ctl --list-formats -d /dev/video0//获取所有参数 v4l2-ctl --list-formats-ext -d /dev/video0//ffmpeg -f dshow -list_devices true -i dummyQStringList FFmpegDevice::getInputDevices(const char *flag){ FFmpegHelper::initLib(); //启用日志回调接收输出信息 av_log_set_callback(FFmpegDevice::logCallback); //设置相关参数以便记录对应结果 FFmpegDevice::logType = "list_devices"; FFmpegDevice::logFlag.clear(); FFmpegDevice::logResult.clear(); AVFormatContext *ctx = avformat_alloc_context(); AVInputFormatx *fmt = av_find_input_format(flag); AVDictionary *opts = NULL; av_dict_set(&opts, "list_devices", "true", 0); if (strcmp(flag, "vfwcap") == 0) { avformat_open_input(&ctx, "list", fmt, NULL); } else if (strcmp(flag, "dshow") == 0) { avformat_open_input(&ctx, "dummy", fmt, &opts); } else { avformat_open_input(&ctx, "", fmt, &opts); } //释放资源 av_dict_free(&opts); avformat_close_input(&ctx); //重新设置日志回调以便恢复原样 av_log_set_callback(av_log_default_callback); //取出日志结果 return FFmpegDevice::logResult;}QStringList FFmpegDevice::getDeviceOption(const QString &url){ const char *flag = (url.startsWith("video=") ? Device_Video : Device_Audio); QString device = url;#ifndef Q_OS_WIN device.replace("video=", ""); device.replace("audio=", "");#endif return FFmpegDevice::getDeviceOption(flag, device);}//ffmpeg -f dshow -list_options true -i video="Webcam"QStringList FFmpegDevice::getDeviceOption(const char *flag, const QString &device){ FFmpegHelper::initLib(); //启用日志回调接收输出信息 av_log_set_callback(FFmpegDevice::logCallback); //设置相关参数以便记录对应结果 FFmpegDevice::logType = "list_options"; FFmpegDevice::logFlag.clear(); FFmpegDevice::logResult.clear(); AVFormatContext *ctx = avformat_alloc_context(); AVInputFormatx *fmt = av_find_input_format(flag); AVDictionary *opts = NULL; av_dict_set(&opts, "list_options", "true", 0); avformat_open_input(&ctx, device.toUtf8().constData(), fmt, &opts); //释放资源 av_dict_free(&opts); avformat_close_input(&ctx); //重新设置日志回调以便恢复原样 av_log_set_callback(av_log_default_callback); //取出日志结果 return FFmpegDevice::logResult;}#ifdef ffmpegdeviceQStringList FFmpegDevice::getInputDevices(bool video){ FFmpegHelper::initLib(); //测试发现从ffmpeg5开始才能获取到值(以前的版本内部没有实现) QStringList names; AVDeviceInfoList *devices = NULL; AVInputFormatx *fmt = NULL; fmt = av_find_input_format(video ? Device_Video : Device_Audio); if (fmt) { if (avdevice_list_input_sources(fmt, NULL, NULL, &devices) >= 0) { names = getDeviceNames(devices, video); } } return names;}QStringList FFmpegDevice::getDeviceNames(bool input, bool video){ FFmpegHelper::initLib(); QStringList names; AVDeviceInfoList *devices = NULL; if (input) { AVInputFormatx *fmt = NULL; do { names.clear(); fmt = (video ? av_input_video_device_next(fmt) : av_input_audio_device_next(fmt)); if (fmt) { if (avdevice_list_input_sources(fmt, NULL, NULL, &devices) >= 0) { names = getDeviceNames(devices, video); } //qDebug() << "input" << fmt->name << names; } } while (fmt); } else { AVOutputFormatx *fmt = NULL; do { names.clear(); fmt = (video ? av_output_video_device_next(fmt) : av_output_audio_device_next(fmt)); if (fmt) { if (avdevice_list_output_sinks(fmt, NULL, NULL, &devices) >= 0) { names = getDeviceNames(devices, video); } //qDebug() << "output" << fmt->name << names; } } while (fmt); } return names;}QStringList FFmpegDevice::getDeviceNames(AVDeviceInfoList *devices, bool video){ QStringList names; int count = devices->nb_devices; for (int i = 0; i < count; ++i) { AVDeviceInfo *device = devices->devices[i];#if (FFMPEG_VERSION_MAJOR > 4) if (device->nb_media_types > 0) { AVMediaType type = *device->media_types; if ((video && type != AVMEDIA_TYPE_VIDEO) || (!video && type != AVMEDIA_TYPE_AUDIO)) { continue; } }#endif //在win上设备名传描述符/linux是设备名#ifdef Q_OS_WIN names << device->device_description;#else names << device->device_name;#endif } //释放设备列表 avdevice_free_list_devices(&devices); return names;}#endif 