视频手术刀 video bistoury（二）--ffmpeg 基石

来源：互联网发布：c语言中多个if else 编辑：程序博客网时间：2024/06/08 18:00

ffmpeg作为视频编解码的基石，其重要性不言而喻，本篇介绍ffmpeg在VideoBistoury中的封装结构。

ffmpeg_frame

通过ffmpeg_frame 统一管理解码后的音频帧、视频帧

class FFrame{ public:    BYTE *data;    bool hasVideo = false;    bool hasAudio = false;    int length;    int width;    int height;    double     int nChannels;    int sampleRate;    uint64_t channel_layout;}

ffmpeg_capturer

抓帧神器

引入的头
注意使用 extern “C”

extern "C" {#include "libavcodec/avcodec.h" 编解码器#include "libavformat/avformat.h" 封装格式#include "libavutil/avutil.h" #include "libswscale/swscale.h" 用于图像变换#include "libswresample/swresample.h" 用于音频变换};#include "ffmpeg_frame.h"

基本数据结构

private:    char *m_video_path;    AVFormatContext *av_fmt_ctx;    int video_index = -1;    int audio_index = -1;    AVCodecContext *video_codec_ctx;    AVCodecContext *audio_codec_ctx;    AVCodec *video_codec, *audio_codec;    AVPacket *packet;    AVFrame *video_frame;    AVFrame *video_RGB_frame;    AVFrame *audio_frame;    SwsContext *sws_ctx;    SwrContext *swr_ctx;    uint8_t *rgb_frame_buffer;    int rgb_picture_size;    double current_pts = 0;    /**audio**/    int out_audio_samplerate = 0;    int out_audio_channels = 0;    uint64_t out_audio_channel_layout;    AVSampleFormat out_audio_sample_fmt = AV_SAMPLE_FMT_S16;

状态机，参考播放器状态机
prepare:采集视频基本信息，包括size、avformat、avstream、avcodec、timebase

    av_register_all();    avcodec_register_all();    av_fmt_ctx = avformat_alloc_context();    int ret;    ret = avformat_open_input(&av_fmt_ctx, m_video_path, NULL, NULL);    printf("opengl video result :%d\n", ret);    if (ret < 0) {        printf("open video failed %d\n", ret);        return;    }    for (int i = 0; i < av_fmt_ctx->nb_streams; ++i) {        if (av_fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {            video_index = i;        }        if (av_fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {            audio_index = i;        }    }    if (video_index < 0 || audio_index < 0) {        printf("can not find video index or audio index\n");        return;    }    video_time_base = av_q2d(av_fmt_ctx->streams[video_index]->time_base);    video_frame_rate = av_q2d(av_fmt_ctx->streams[video_index]->r_frame_rate);    auto video_codec_par = av_fmt_ctx->streams[video_index]->codecpar;    auto audio_codec_par = av_fmt_ctx->streams[audio_index]->codecpar;    video_codec = avcodec_find_decoder(video_codec_par->codec_id);    audio_codec = avcodec_find_decoder(audio_codec_par->codec_id);    video_codec_ctx = avcodec_alloc_context3(video_codec);    audio_codec_ctx = avcodec_alloc_context3(audio_codec);    width = video_codec_ctx->width;    height = video_codec_ctx->height;    avcodec_parameters_to_context(video_codec_ctx, video_codec_par);    avcodec_parameters_to_context(audio_codec_ctx, audio_codec_par);    if (avcodec_open2(video_codec_ctx, video_codec, NULL) < 0) {        printf("open video codec failed\n");    }    if (avcodec_open2(audio_codec_ctx, audio_codec, NULL) < 0) {        printf("open audio codec failed\n");    }

start:
开辟解码前后的中间缓存（packet、YUV帧video_frame、RGB帧video_RGB_frame、audio_frame）
构造帧格式转换的context(视频帧sws_ctx、音频帧swr_ctx)

packet = av_packet_alloc();av_init_packet(packet);video_frame = av_frame_alloc();video_RGB_frame = av_frame_alloc();audio_frame = av_frame_alloc();sws_ctx = sws_getContext(video_codec_ctx->width, video_codec_ctx->height, getPixFormat(),                         video_codec_ctx->width, video_codec_ctx->height, AV_PIX_FMT_RGB24, SWS_BICUBIC,                         NULL, NULL, NULL);rgb_picture_size = avpicture_get_size(AV_PIX_FMT_RGB24, video_codec_ctx->width, video_codec_ctx->height);rgb_frame_buffer = (uint8_t *) (av_mallocz(rgb_picture_size));avpicture_fill((AVPicture *) video_RGB_frame, rgb_frame_buffer, AV_PIX_FMT_RGB24,               video_codec_ctx->width, video_codec_ctx->height);/**audio**/auto in_audio_channels = av_get_channel_layout_nb_channels(audio_codec_ctx->channel_layout);auto in_audio_sample_fmt = audio_codec_ctx->sample_fmt;auto in_audio_samplerate = audio_codec_ctx->sample_rate;auto in_audio_channel_layout = audio_codec_ctx->channel_layout;out_audio_channels = in_audio_channels;out_audio_samplerate = in_audio_samplerate;out_audio_sample_fmt = AV_SAMPLE_FMT_S16;out_audio_channel_layout = audio_codec_ctx->channel_layout;out_audio_length = av_samples_get_buffer_size(NULL, out_audio_channels, NB_SAMPLES, out_audio_sample_fmt, 1);swr_ctx = swr_alloc_set_opts(NULL,                             out_audio_channel_layout, out_audio_sample_fmt, out_audio_samplerate,                             in_audio_channel_layout, in_audio_sample_fmt, in_audio_samplerate,                             0, 0);swr_init(swr_ctx);av_dump_format(av_fmt_ctx, 0, m_video_path, 0);

captureFrame:抓取一帧。调用者通过外部循环去抓取视频每一帧
视频帧解码为YUV、YUV转RGB，对于PC抓取的数据是倒的，这里需要颠倒处理；这一步可以拆开，在显示时进行YUV转RGB，毕竟YUV内存占用量比RGB小不少
音频帧解码、重采样格式转换；
pts设置；
时间基转化与设置

FFrame *FFmpegCapturer::captureFrame() {    int ret;    int got_picture;    int got_frame;    double pts = 0;    ret = av_read_frame(av_fmt_ctx, packet);    if (ret < 0) {        printf("read no frame\n");        return NULL;    }    auto fframe = new FFrame();//    video    if (packet->stream_index == video_index) {        ret = avcodec_decode_video2(video_codec_ctx, video_frame, &got_picture, packet);//        ret = avcodec_send_packet(video_codec_ctx, packet);        if (ret < 0) {            printf("decode video failed\n");        }        if (packet->dts == AV_NOPTS_VALUE            && video_frame->opaque            && *(uint64_t *) video_frame->opaque != AV_NOPTS_VALUE) {            pts = *(uint64_t *) video_frame->opaque;        } else if (packet->dts != AV_NOPTS_VALUE) {            pts = packet->dts;        } else {            pts = 0;        }        pts *= av_q2d(av_fmt_ctx->streams[video_index]->time_base);        if (got_picture) {//            auto pts = av_frame_get_best_effort_timestamp(video_frame);            video_frame->data[0] += video_frame->linesize[0] * (video_codec_ctx->height - 1);            video_frame->linesize[0] *= -1;            video_frame->data[1] += video_frame->linesize[1] * (video_codec_ctx->height / 2 - 1);            video_frame->linesize[1] *= -1;            video_frame->data[2] += video_frame->linesize[2] * (video_codec_ctx->height / 2 - 1);            video_frame->linesize[2] *= -1;            sws_scale(sws_ctx, (const uint8_t *const *) (video_frame->data),                      video_frame->linesize, 0, video_codec_ctx->height,                      video_RGB_frame->data, video_RGB_frame->linesize);            fframe->hasVideo = true;            fframe->width = video_codec_ctx->width;            fframe->height = video_codec_ctx->height;            fframe->length = rgb_picture_size;            fframe->data = (BYTE *) av_mallocz(rgb_picture_size);            fframe->pts = current_pts + pts;//            printf("frame linesize %d length %d \n", video_RGB_frame->linesize[0], rgb_picture_size);            memcpy(fframe->data, video_RGB_frame->data[0], rgb_picture_size);        }    }//    audio    if (packet->stream_index == audio_index) {        ret = avcodec_decode_audio4(audio_codec_ctx, audio_frame, &got_frame, packet);        if (ret < 0) {            printf("decode audio failed\n");        }        if (packet->dts == AV_NOPTS_VALUE            && audio_frame->opaque            && *(uint64_t *) audio_frame->opaque != AV_NOPTS_VALUE) {            pts = *(uint64_t *) audio_frame->opaque;        } else if (packet->dts != AV_NOPTS_VALUE) {            pts = packet->dts;        } else {            pts = 0;        }//        av_rescale_q()时间基转换        pts *= av_q2d(av_fmt_ctx->streams[audio_index]->time_base);//转换为秒        if (got_frame) {//            todo            uint8_t *out_buffer = (uint8_t *) av_mallocz(MAX_AUDIO_FRAME_SZIE * 2);            int len = swr_convert(swr_ctx, &out_buffer, MAX_AUDIO_FRAME_SZIE,                                  (const uint8_t **) (audio_frame->data), audio_frame->nb_samples);            fframe->hasAudio = true;            fframe->data = out_buffer;            fframe->nChannels = out_audio_channels;            fframe->sampleRate = out_audio_samplerate;            fframe->length = av_samples_get_buffer_size(0, out_audio_channels, len, out_audio_sample_fmt, 1);            fframe->pts = current_pts + pts;            memcpy(fframe->data, out_buffer, fframe->length);        }    }//    current_pts += pts;    av_packet_unref(packet);    return fframe;}

release:最后一定要记得释放

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