title: ffmpeg_sample解讀_filtering_video
date: 2020-10-28 10:15:02
tags: [讀書筆記]
typora-copy-images-to: ./imgs
typora-root-url: ./imgs

總結(jié)

和之前的類似.初始化過濾器.從參數(shù)中讀進(jìn)來str也會(huì)轉(zhuǎn)換成過濾器.然后把他們連接起來,冉家解碼視頻.取出解碼后的幀,送入過濾器處理.取出處理完的幀,然后展示出來.流程和前幾個(gè)過濾器的都差不多.主要都是在看過濾器的連接和添加

流程圖

graph TB
 if[init_filters]
 -->afgbn[avfilter_get_by_name]
 -->afia[avfilter_inout_alloc]
 -->afga[avfilter_graph_alloc]
 -->afgcf[avfilter_graph_create_filter]
 -->aosil[av_opt_set_int_list]
 -->afgpp[avfilter_graph_parse_ptr]
 -->afgc[avfilter_graph_config]
 -->arf{av_read_frame>0?}
 -->|yes|acsp[avcodec_send_packet]
 arf-->|no|free[free]
 acsp-->acrf{avcodec_receive_frame>0?}
 -->|no|free[free]
 acrf-->|yes|abaff[av_buffersrc_add_frame_flags]
 -->absgf[av_buffersink_get_frame]
 -->df[display_frame]
 -->free[free]

image-20201029112249767

代碼

/**
 * @file
 * API example for decoding and filtering
 * @example filtering_video.c
 */

#define _XOPEN_SOURCE 600 /* for usleep */
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
#include <libavutil/opt.h>

const char *filter_descr = "scale=78:24,transpose=cclock";
/* other way:
   scale=78:24 [scl]; [scl] transpose=cclock // assumes "[in]" and "[out]" to be input output pads respectively
 */

static AVFormatContext *fmt_ctx;
static AVCodecContext *dec_ctx;
AVFilterContext *buffersink_ctx;//出參的過濾器上下文
AVFilterContext *buffersrc_ctx;//入?yún)⒌倪^濾器上下文
AVFilterGraph *filter_graph;
static int video_stream_index = -1;
static int64_t last_pts = AV_NOPTS_VALUE;

/**
 * 打開輸入文件,和音頻處理類似. 解碼出幀后.放入過濾器中處理
 * 過濾器有一個(gè)輸入過濾器,一個(gè)輸出過濾器.中又混合了string組成的過濾器.通過 AVFilterGraph 連接起來
 * @param filename
 * @return
 */
static int open_input_file(const char *filename)
{
    int ret;
    AVCodec *dec;
//打開文件.創(chuàng)建ftm_ctx格式上下文
    if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
        return ret;
    }
//找到合適的流信息
    if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
        return ret;
    }

    /* select the video stream */
    //選擇視頻流,得到索引,獲取解碼器
    ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n");
        return ret;
    }
    video_stream_index = ret;
//創(chuàng)建解碼器上下文
    /* create decoding context */
    dec_ctx = avcodec_alloc_context3(dec);
    if (!dec_ctx)
        return AVERROR(ENOMEM);
    //把視頻流中的解碼參數(shù)拷貝到解碼器上下文中
    avcodec_parameters_to_context(dec_ctx, fmt_ctx->streams[video_stream_index]->codecpar);

    /* init the video decoder */
    //用解碼器來設(shè)置解碼器上下文的參數(shù)
    if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");
        return ret;
    }

    return 0;
}
/**
 * 初始化過濾器
 * @param filters_descr
 * @return
 */
static int init_filters(const char *filters_descr)
{
    char args[512];
    int ret = 0;
    //數(shù)據(jù)輸入輸出過濾器以及 分配的輸入輸出buf
    const AVFilter *buffersrc  = avfilter_get_by_name("buffer");
    const AVFilter *buffersink = avfilter_get_by_name("buffersink");
    AVFilterInOut *outputs = avfilter_inout_alloc();
    AVFilterInOut *inputs  = avfilter_inout_alloc();
    AVRational time_base = fmt_ctx->streams[video_stream_index]->time_base;
    enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };

    //初始化過濾器圖形.用來連接多個(gè)過濾器
    filter_graph = avfilter_graph_alloc();
    if (!outputs || !inputs || !filter_graph) {
        ret = AVERROR(ENOMEM);
        goto end;
    }
    //把參數(shù)都寫到 args里
    /* buffer video source: the decoded frames from the decoder will be inserted here. */
    snprintf(args, sizeof(args),
            "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
            dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,
            time_base.num, time_base.den,
            dec_ctx->sample_aspect_ratio.num, dec_ctx->sample_aspect_ratio.den);
//用args 參數(shù)和buufersrc初始化過濾器上下文,并添加到 過濾器圖形中, 返回改過濾器上下文
    ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
                                       args, NULL, filter_graph);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");
        goto end;
    }
//初始化另一個(gè)過濾器上下文,添加到過濾器圖形匯總,
    /* buffer video sink: to terminate the filter chain. */
    ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
                                       NULL, NULL, filter_graph);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");
        goto end;
    }

    //設(shè)置 pix_fmts屬性
    ret = av_opt_set_int_list(buffersink_ctx, "pix_fmts", pix_fmts,
                              AV_PIX_FMT_NONE, AV_OPT_SEARCH_CHILDREN);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");
        goto end;
    }

    /*
     * Set the endpoints for the filter graph. The filter_graph will
     * be linked to the graph described by filters_descr.
     */

    /*
     * The buffer source output must be connected to the input pad of
     * the first filter described by filters_descr; since the first
     * filter input label is not specified, it is set to "in" by
     * default.
     */
    //把兩個(gè)輸入輸出的 上下文綁定到這兩個(gè) inout的結(jié)構(gòu)體上,
    // 這里我理解是,因?yàn)橛袀€(gè)字符串傳入的過濾器.這里是一種連接字符串產(chǎn)生的過濾器和上邊創(chuàng)建過濾器的方式
    outputs->name       = av_strdup("in");
    outputs->filter_ctx = buffersrc_ctx;
    outputs->pad_idx    = 0;
    outputs->next       = NULL;

    /*
     * The buffer sink input must be connected to the output pad of
     * the last filter described by filters_descr; since the last
     * filter output label is not specified, it is set to "out" by
     * default.
     */
    //這個(gè)輸出的input結(jié)構(gòu)體必須和 desrc 里的最好一個(gè)過濾器相連
    inputs->name       = av_strdup("out");
    inputs->filter_ctx = buffersink_ctx;
    inputs->pad_idx    = 0;
    inputs->next       = NULL;
//把字符串解析出的過濾器和 inout 中的輸入輸出過濾器連接起來
    if ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,
                                    &inputs, &outputs, NULL)) < 0)
        goto end;
//進(jìn)行配置
    if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
        goto end;

end:
    avfilter_inout_free(&inputs);
    avfilter_inout_free(&outputs);

    return ret;
}

static void display_frame(const AVFrame *frame, AVRational time_base)
{
    int x, y;
    uint8_t *p0, *p;
    int64_t delay;

    if (frame->pts != AV_NOPTS_VALUE) {
        if (last_pts != AV_NOPTS_VALUE) {
            /* sleep roughly the right amount of time;
             * usleep is in microseconds, just like AV_TIME_BASE. */
            delay = av_rescale_q(frame->pts - last_pts,
                                 time_base, AV_TIME_BASE_Q);
            if (delay > 0 && delay < 1000000)
                usleep(delay);
        }
        last_pts = frame->pts;
    }

    /* Trivial ASCII grayscale display. */
    p0 = frame->data[0];
    puts("\033c");
    for (y = 0; y < frame->height; y++) {
        p = p0;
        for (x = 0; x < frame->width; x++)
            putchar(" .-+#"[*(p++) / 52]);
        putchar('\n');
        p0 += frame->linesize[0];
    }
    fflush(stdout);
}

int filtering_video_main(int argc, char **argv)
{
    int ret;
    AVPacket packet;
    AVFrame *frame;
    AVFrame *filt_frame;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s file\n", argv[0]);
        exit(1);
    }

    frame = av_frame_alloc();
    filt_frame = av_frame_alloc();
    if (!frame || !filt_frame) {
        perror("Could not allocate frame");
        exit(1);
    }

    if ((ret = open_input_file(argv[1])) < 0)
        goto end;
    if ((ret = init_filters(filter_descr)) < 0)
        goto end;

    /* read all packets */
    while (1) {
        //讀取packet
        if ((ret = av_read_frame(fmt_ctx, &packet)) < 0)
            break;
//處理視頻
        if (packet.stream_index == video_stream_index) {
            //數(shù)據(jù)發(fā)送到解碼器
            ret = avcodec_send_packet(dec_ctx, &packet);
            if (ret < 0) {
                av_log(NULL, AV_LOG_ERROR, "Error while sending a packet to the decoder\n");
                break;
            }

            while (ret >= 0) {

                //解碼器中取出幀
                ret = avcodec_receive_frame(dec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    av_log(NULL, AV_LOG_ERROR, "Error while receiving a frame from the decoder\n");
                    goto end;
                }

                frame->pts = frame->best_effort_timestamp;

                /* push the decoded frame into the filtergraph */
                //把解碼后的幀數(shù)據(jù)放入過濾器圖中處理,
                if (av_buffersrc_add_frame_flags(buffersrc_ctx, frame, AV_BUFFERSRC_FLAG_KEEP_REF) < 0) {
                    av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
                    break;
                }

                /* pull filtered frames from the filtergraph */
                while (1) {//的到過濾器處理完的結(jié)果.輸出幀
                    ret = av_buffersink_get_frame(buffersink_ctx, filt_frame);
                    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                        break;
                    if (ret < 0)
                        goto end;
                    //展示幀數(shù)據(jù).釋放幀
                    display_frame(filt_frame, buffersink_ctx->inputs[0]->time_base);
                    av_frame_unref(filt_frame);
                }
                av_frame_unref(frame);
            }
        }
        av_packet_unref(&packet);
    }
end:
    avfilter_graph_free(&filter_graph);
    avcodec_free_context(&dec_ctx);
    avformat_close_input(&fmt_ctx);
    av_frame_free(&frame);
    av_frame_free(&filt_frame);

    if (ret < 0 && ret != AVERROR_EOF) {
        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
        exit(1);
    }

    exit(0);
}