在https://blog.csdn.net/fengbingchun/article/details/94712986 中介紹過如果usb視頻流編碼類型為rawvideo則無需進行解碼，可直接通過av_read_frame獲取視頻流然后再通過sws_scale進行像素格式轉換，當在高分辨率情況下，有時達不到實時顯示，會有卡頓，經分析，性能瓶頸在av_read_frame和sws_scale，由于在https://blog.csdn.net/fengbingchun/article/details/94712986中將此兩個函數放在一個線程中串行執行因此導致卡頓。這里將兩個函數放在兩個獨立的線程中并行執行，一個線程負責執行av_read_frame，另一個線程負責執行sws_scale，性能得到大幅提升。

測試代碼如下：

common.hpp:

#ifndef FBC_FFMPEG_TEST_COMMON_HPP_
#define FBC_FFMPEG_TEST_COMMON_HPP_#include <chrono>
#include <queue>
#include <mutex>
#include <condition_variable>class Timer {
public:static long long getNowTime() { // millisecondsauto now = std::chrono::system_clock::now();return std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch()).count();}
};typedef struct Buffer {unsigned char* data;unsigned int length;
} Buffer;class BufferQueue {
public:BufferQueue() = default;~BufferQueue() {}void push(Buffer& buffer) {std::unique_lock<std::mutex> lck(mtx);queue.push(buffer);cv.notify_all();}void pop(Buffer& buffer) {std::unique_lock<std::mutex> lck(mtx);while (queue.empty()) {cv.wait(lck);}buffer = queue.front();queue.pop();}unsigned int size() {return queue.size();}private:std::queue<Buffer> queue;std::mutex mtx;std::condition_variable cv;
};class PacketScaleQueue {
public:PacketScaleQueue() = default;~PacketScaleQueue() {Buffer buffer;while (getPacketSize() > 0) {popPacket(buffer);delete[] buffer.data;}while (getScaleSize() > 0) {popScale(buffer);delete[] buffer.data;}}void init(unsigned int buffer_num = 16, unsigned int buffer_size = 1024 * 1024 * 4) {for (unsigned int i = 0; i < buffer_num; ++i) {Buffer buffer = { new unsigned char[buffer_size], buffer_num};pushPacket(buffer);}}void pushPacket(Buffer& buffer) { packet_queue.push(buffer); }void popPacket(Buffer& buffer) { packet_queue.pop(buffer); }unsigned int getPacketSize() { return packet_queue.size(); }void pushScale(Buffer& buffer) { scale_queue.push(buffer); }void popScale(Buffer& buffer) { scale_queue.pop(buffer); }unsigned int getScaleSize() { return scale_queue.size(); }private:BufferQueue packet_queue, scale_queue;
};#endif // FBC_FFMPEG_TEST_COMMON_HPP_

test_ffmpeg_decode_show.cpp:

#include "funset.hpp"
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <memory>
#include <fstream>
#include <thread>
#include "common.hpp"#ifdef __cplusplus
extern "C" {
#endif#include <libavdevice/avdevice.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
#include <libavutil/mem.h>
#include <libavutil/imgutils.h>#ifdef __cplusplus
}
#endif#include <opencv2/opencv.hpp>namespace {bool packet_scale_flag = true;void get_packet(AVFormatContext* format_ctx, int video_stream_index, PacketScaleQueue& packet_scale)
{//for (int i = 0; i < 100; ++i) {while (packet_scale_flag) {AVPacket packet;//long long t1 = Timer::getNowTime();int ret = av_read_frame(format_ctx, &packet);//long long t2 = Timer::getNowTime();//fprintf(stdout, "av_read frame cost time: %lldms\n", t2 - t1);if (ret >= 0 && packet.stream_index == video_stream_index && packet.size > 0) {Buffer buffer;packet_scale.popPacket(buffer);memcpy(buffer.data, packet.data, packet.size);packet_scale.pushScale(buffer);av_packet_unref(&packet);} else {fprintf(stderr, "##### fail to av_read_frame: %d, %d\n", ret, packet.size);}}
}void get_scale(AVCodecContext* codec_ctx, PacketScaleQueue& packet_scale)
{SwsContext* sws_ctx = sws_getContext(codec_ctx->width, codec_ctx->height, codec_ctx->pix_fmt, codec_ctx->width, codec_ctx->height, AV_PIX_FMT_BGR24, 0, nullptr, nullptr, nullptr);if (!sws_ctx) {fprintf(stderr, "##### fail to sws_getContext\n");}uint8_t *bgr_data[4], *yuyv422_data[4];int bgr_linesize[4], yuyv422_linesize[4];av_image_alloc(bgr_data, bgr_linesize, codec_ctx->width, codec_ctx->height, AV_PIX_FMT_BGR24, 1);av_image_alloc(yuyv422_data, yuyv422_linesize, codec_ctx->width, codec_ctx->height, AV_PIX_FMT_YUYV422, 1);cv::Mat mat(codec_ctx->height, codec_ctx->width, CV_8UC3);const char* winname = "usb video";cv::namedWindow(winname);//for (int i = 0; i < 100; ++i) {while (packet_scale_flag) {Buffer buffer;packet_scale.popScale(buffer);const uint8_t *srcSlice[1];srcSlice[0] = buffer.data;//long long t1 = Timer::getNowTime();sws_scale(sws_ctx, srcSlice, yuyv422_linesize, 0, codec_ctx->height, bgr_data, bgr_linesize);//long long t2 = Timer::getNowTime();//fprintf(stdout, "sws_scale cost time: %lldms\n", t2 - t1);packet_scale.pushPacket(buffer);mat.data = bgr_data[0];cv::imshow(winname, mat);//cv::imwrite("xxx.jpg", mat);int key = cv::waitKey(10);if (key == 27) { packet_scale_flag = false;break;}}cv::destroyWindow(winname);sws_freeContext(sws_ctx);av_freep(&bgr_data[0]);av_freep(&yuyv422_data[0]);
}} // namespaceint test_ffmpeg_stream_show_two_thread()
{avdevice_register_all();#ifdef _MSC_VERconst char* input_format_name = "vfwcap";const char* url = "";
#elseconst char* input_format_name = "video4linux2";const char* url = "/dev/video0";
#endifAVInputFormat* input_fmt = av_find_input_format(input_format_name);AVFormatContext* format_ctx = avformat_alloc_context();int ret = avformat_open_input(&format_ctx, url, input_fmt, nullptr);if (ret != 0) {fprintf(stderr, "fail to open url: %s, return value: %d\n", url, ret);return -1;}ret = avformat_find_stream_info(format_ctx, nullptr);if (ret < 0) {fprintf(stderr, "fail to get stream information: %d\n", ret);return -1;}int video_stream_index = -1;for (unsigned int i = 0; i < format_ctx->nb_streams; ++i) {const AVStream* stream = format_ctx->streams[i];if (stream->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {video_stream_index = i;fprintf(stdout, "type of the encoded data: %d, dimensions of the video frame in pixels: width: %d, height: %d, pixel format: %d\n",stream->codecpar->codec_id, stream->codecpar->width, stream->codecpar->height, stream->codecpar->format);}}if (video_stream_index == -1) {fprintf(stderr, "no video stream\n");return -1;}AVCodecParameters* codecpar = format_ctx->streams[video_stream_index]->codecpar;const AVCodec* codec = avcodec_find_decoder(codecpar->codec_id);if (!codec) {fprintf(stderr, "fail to avcodec_find_decoder\n");return -1;}if (codecpar->codec_id != AV_CODEC_ID_RAWVIDEO) {fprintf(stderr, "this test code only support rawvideo encode: %d\n", codecpar->codec_id);return -1;}AVCodecContext* codec_ctx = avcodec_alloc_context3(codec);if (!codec_ctx) {fprintf(stderr, "fail to avcodec_alloc_context3\n");return -1;}codec_ctx->pix_fmt = AVPixelFormat(codecpar->format);codec_ctx->height = codecpar->height;codec_ctx->width = codecpar->width;codec_ctx->thread_count = 16;ret = avcodec_open2(codec_ctx, codec, nullptr);if (ret != 0) {fprintf(stderr, "fail to avcodec_open2: %d\n", ret);return -1;}PacketScaleQueue packet_scale;packet_scale.init(16, 1024*1024*4);std::thread thread_packet(get_packet, format_ctx, video_stream_index, std::ref(packet_scale));std::thread thread_scale(get_scale, codec_ctx, std::ref(packet_scale));thread_packet.join();thread_scale.join();avformat_close_input(&format_ctx);fprintf(stdout, "test finish\n");return 0;
}

執行結果如下：

GitHub：https://github.com/fengbingchun/OpenCV_Test

總結

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