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

總結(jié)

• 硬件解碼數(shù)據(jù),其實和軟解碼比較類似. 都是初始化解碼器上下文,配置參數(shù),然后讀取packet數(shù)據(jù)送入解碼器,取出freme.
• 硬解碼需要初始化硬件解碼上下文,然后把上下文綁定到解碼器上下文上

流程圖

graph TB
ahftbn[av_hwdevice_find_type_by_name]
-->afoi[avformat_open_input]
-->affsi[avformat_find_stream_info]
-->afbs[av_find_best_stream]
-->acghc[avcodec_get_hw_config]
-->alc[avcodec_alloc_context3]
-->acptc[avcodec_parameters_to_context]
-->hdi[hw_decoder_init]
-->ahcc[av_hwdevice_ctx_create]
-->aco[avcodec_open2]
-->arf{av_read_frame>0?}
arf-->|no|release
arf -->|yes|dw[decode_write]
-->acsp[avcodec_send_packet]
-->afa[av_frame_alloc]
-->acrf{avcodec_receive_frame>0}
-->|yes|ahftd[av_hwframe_transfer_data]
-->aigbs[av_image_get_buffer_size]
-->aictb[av_image_copy_to_buffer]
-->acrf
acrf-->|no|release

image-20201029170355411

代碼

/**
 * @file
 * HW-Accelerated decoding example.
 *
 * @example hw_decode.c
 * This example shows how to do HW-accelerated decoding with output
 * frames from the HW video surfaces.
 */

#include <stdio.h>

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/pixdesc.h>
#include <libavutil/hwcontext.h>
#include <libavutil/opt.h>
#include <libavutil/avassert.h>
#include <libavutil/imgutils.h>

static AVBufferRef *hw_device_ctx = NULL;
static enum AVPixelFormat hw_pix_fmt;
static FILE *output_file = NULL;

static int hw_decoder_init(AVCodecContext *ctx, const enum AVHWDeviceType type) {
    int err = 0;

    //根據(jù)類型.找到合適的硬件解碼器上下文,硬解碼的相關(guān)信息在hw_device中
    if ((err = av_hwdevice_ctx_create(&hw_device_ctx, type,
                                      NULL, NULL, 0)) < 0) {
        fprintf(stderr, "Failed to create specified HW device.\n");
        return err;
    }
    //把硬解碼上下文保存在解碼器上下文中.同時釋放原有的引用,拷貝新的引用
    ctx->hw_device_ctx = av_buffer_ref(hw_device_ctx);

    return err;
}

//獲取硬件格式
static enum AVPixelFormat get_hw_format(AVCodecContext *ctx,
                                        const enum AVPixelFormat *pix_fmts) {
    const enum AVPixelFormat *p;

    for (p = pix_fmts; *p != -1; p++) {
        if (*p == hw_pix_fmt)
            return *p;
    }

    fprintf(stderr, "Failed to get HW surface format.\n");
    return AV_PIX_FMT_NONE;
}

static int decode_write(AVCodecContext *avctx, AVPacket *packet) {
    AVFrame *frame = NULL, *sw_frame = NULL;
    AVFrame *tmp_frame = NULL;
    uint8_t *buffer = NULL;
    int size;
    int ret = 0;
//數(shù)據(jù)送入解碼器,
    ret = avcodec_send_packet(avctx, packet);
    if (ret < 0) {
        fprintf(stderr, "Error during decoding\n");
        return ret;
    }

    while (1) {
        //分配解碼幀
        if (!(frame = av_frame_alloc()) || !(sw_frame = av_frame_alloc())) {
            fprintf(stderr, "Can not alloc frame\n");
            ret = AVERROR(ENOMEM);
            goto fail;
        }
// 獲取解碼后的數(shù)據(jù)
        ret = avcodec_receive_frame(avctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            av_frame_free(&frame);
            av_frame_free(&sw_frame);
            return 0;
        } else if (ret < 0) {
            fprintf(stderr, "Error while decoding\n");
            goto fail;
        }

        if (frame->format == hw_pix_fmt) {
            /* retrieve data from GPU to CPU */
            //解碼后的數(shù)據(jù)frame送入,然后取回數(shù)據(jù)到sw_frame
            if ((ret = av_hwframe_transfer_data(sw_frame, frame, 0)) < 0) {
                fprintf(stderr, "Error transferring the data to system memory\n");
                goto fail;
            }
            tmp_frame = sw_frame;
        } else
            tmp_frame = frame;
//輸出數(shù)據(jù)大小
        size = av_image_get_buffer_size(tmp_frame->format, tmp_frame->width,
                                        tmp_frame->height, 1);
        buffer = av_malloc(size);
        if (!buffer) {
            fprintf(stderr, "Can not alloc buffer\n");
            ret = AVERROR(ENOMEM);
            goto fail;
        }
        //把圖片數(shù)據(jù)tmp_frame->data,拷貝到一個buf中 .后邊會寫出buf
        ret = av_image_copy_to_buffer(buffer, size,
                                      (const uint8_t *const *) tmp_frame->data,
                                      (const int *) tmp_frame->linesize, tmp_frame->format,
                                      tmp_frame->width, tmp_frame->height, 1);
        if (ret < 0) {
            fprintf(stderr, "Can not copy image to buffer\n");
            goto fail;
        }
//寫到文件中
        if ((ret = fwrite(buffer, 1, size, output_file)) < 0) {
            fprintf(stderr, "Failed to dump raw data.\n");
            goto fail;
        }

        fail:
        av_frame_free(&frame);
        av_frame_free(&sw_frame);
        av_freep(&buffer);
        if (ret < 0)
            return ret;
    }
}

/***
 * 硬件解碼數(shù)據(jù),其實和軟解碼比較類似. 都是初始化解碼器上下文,配置參數(shù),然后讀取packet數(shù)據(jù)送入解碼器,取出freme.
 * 硬解碼需要初始化硬件解碼上下文,然后把上下文綁定到解碼器上下文上
 * @param argc
 * @param argv
 * @return
 * 優(yōu)點(diǎn)：

比軟件處理速度快。
減少CPU的負(fù)荷餐胀，更省電。
避免數(shù)據(jù)拷貝否灾。許多硬件解碼器能夠生成輸出到硬件設(shè)備(比如顯存)的surface，這意味渲染輸出之前不需要額外的數(shù)據(jù)拷貝墨技。在某些情況下，它還可以支持硬件設(shè)備的surface輸入與編碼器一起使用健提，以避免在轉(zhuǎn)碼時候的數(shù)據(jù)拷貝伟叛。
缺點(diǎn)：

硬件編碼器生成的輸出質(zhì)量通常比好的軟件編碼器低得多[1]。
硬件加速方案依賴于各硬件和平臺的支持统刮，沒有統(tǒng)一的方案。
對于特定處理(比如編解碼)硬件加速的支持和更新迭代速度慢侥蒙。

作者：smallest_one
鏈接：http://www.reibang.com/p/c3f4daf2aaa3
來源：簡書
著作權(quán)歸作者所有。商業(yè)轉(zhuǎn)載請聯(lián)系作者獲得授權(quán)鞭衩，非商業(yè)轉(zhuǎn)載請注明出處娃善。
 */
int hw_decode_main(int argc, char *argv[]) {
    AVFormatContext *input_ctx = NULL;
    int video_stream, ret;
    AVStream *video = NULL;
    AVCodecContext *decoder_ctx = NULL;
    AVCodec *decoder = NULL;
    AVPacket packet;
    enum AVHWDeviceType type;
    int i;

    if (argc < 4) {
        fprintf(stderr, "Usage: %s <device type> <input file> <output file>\n", argv[0]);
        return -1;
    }
//通過名稱找到硬件解碼器
    type = av_hwdevice_find_type_by_name(argv[1]);
    if (type == AV_HWDEVICE_TYPE_NONE) {
        fprintf(stderr, "Device type %s is not supported.\n", argv[1]);
        fprintf(stderr, "Available device types:");
        while ((type = av_hwdevice_iterate_types(type)) != AV_HWDEVICE_TYPE_NONE)
            fprintf(stderr, " %s", av_hwdevice_get_type_name(type));
        fprintf(stderr, "\n");
        return -1;
    }

    /* open the input file */
    //打開輸入文件.
    if (avformat_open_input(&input_ctx, argv[2], NULL, NULL) != 0) {
        fprintf(stderr, "Cannot open input file '%s'\n", argv[2]);
        return -1;
    }
//找了流信息
    if (avformat_find_stream_info(input_ctx, NULL) < 0) {
        fprintf(stderr, "Cannot find input stream information.\n");
        return -1;
    }
//找到視頻流,獲取解碼器
    /* find the video stream information */
    ret = av_find_best_stream(input_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &decoder, 0);
    if (ret < 0) {
        fprintf(stderr, "Cannot find a video stream in the input file\n");
        return -1;
    }
    video_stream = ret;

    for (i = 0;; i++) {
        //從解碼器中取回硬件解碼器的配置
        const AVCodecHWConfig *config = avcodec_get_hw_config(decoder, i);
        if (!config) {
            fprintf(stderr, "Decoder %s does not support device type %s.\n",
                    decoder->name, av_hwdevice_get_type_name(type));
            return -1;
        }
        //配置信息支持硬件解碼,并且格式匹配
        if (config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX &&
            config->device_type == type) {
            hw_pix_fmt = config->pix_fmt;
            break;
        }
    }
//解碼器上下文分配數(shù)據(jù)
    if (!(decoder_ctx = avcodec_alloc_context3(decoder)))
        return AVERROR(ENOMEM);

    video = input_ctx->streams[video_stream];
    //視頻流信息拷貝到解碼器上下文
    if (avcodec_parameters_to_context(decoder_ctx, video->codecpar) < 0)
        return -1;

    decoder_ctx->get_format = get_hw_format;
//初始化硬件解碼器
    if (hw_decoder_init(decoder_ctx, type) < 0)
        return -1;
//用硬件解碼器的數(shù)據(jù)初始化解碼器上下文
    if ((ret = avcodec_open2(decoder_ctx, decoder, NULL)) < 0) {
        fprintf(stderr, "Failed to open codec for stream #%u\n", video_stream);
        return -1;
    }
//打開寫出文件
    /* open the file to dump raw data */
    output_file = fopen(argv[3], "w+b");

    /* actual decoding and dump the raw data */
    //老流程了.獲取packet.解碼出frame.寫入文件
    while (ret >= 0) {
        if ((ret = av_read_frame(input_ctx, &packet)) < 0)
            break;

        if (video_stream == packet.stream_index)
            //解碼并寫出數(shù)據(jù)
            ret = decode_write(decoder_ctx, &packet);

        av_packet_unref(&packet);
    }
//刷新硬件解碼器最后的數(shù)據(jù)
    /* flush the decoder */
    packet.data = NULL;
    packet.size = 0;
    ret = decode_write(decoder_ctx, &packet);
    av_packet_unref(&packet);

    if (output_file)
        fclose(output_file);
    avcodec_free_context(&decoder_ctx);
    avformat_close_input(&input_ctx);
    av_buffer_unref(&hw_device_ctx);

    return 0;
}