FFmpeg實(shí)現(xiàn)將編碼后數(shù)據(jù)保存成mp4

更新時(shí)間：2023年08月07日 14:13:40 作者：fengbingchun

這篇文章主要為大家詳細(xì)介紹了FFmpeg如何實(shí)現(xiàn)將編碼后數(shù)據(jù)保存成mp4，即從內(nèi)存塊中獲取原始數(shù)據(jù)，然后依次進(jìn)行解碼、編碼、最后保存成mp4視頻文件，感興趣的可以了解一下

以下測(cè)試代碼實(shí)現(xiàn)的功能是：持續(xù)從內(nèi)存塊中獲取原始數(shù)據(jù)，然后依次進(jìn)行解碼、編碼、最后保存成mp4視頻文件。

可保存成單個(gè)視頻文件，也可指定每個(gè)視頻文件的總幀數(shù)，保存多個(gè)視頻文件。

為了便于查看和修改，這里將可獨(dú)立的程序段存放在單個(gè)函數(shù)中：

1.線程函數(shù)set_packet：獨(dú)立線程，用于用戶(hù)向指定的內(nèi)存塊中持續(xù)寫(xiě)入數(shù)據(jù)，這里通過(guò)調(diào)用隊(duì)列類(lèi)PacketScaleQueue，可參考：FFmpeg中AVIOContext的使用方法詳解中說(shuō)明。這里填充的數(shù)據(jù)參考FFmpeg源碼中的doc/examples/encode_video.c：每次向隊(duì)列中寫(xiě)入一幀數(shù)據(jù)

void set_packet(PacketScaleQueue& packet_encode)
{
    while (packet_encode_flag) {
        Buffer buffer;
        packet_encode.popPacket(buffer);
        static int i = 0;
        // refrence: ffmpeg/doc/examples/encode_video.c
        // prepare a dummy image: Y
        unsigned char* p1 = buffer.data;
        for (auto y = 0; y < height; ++y) {
            for (auto x = 0; x < width; ++x) {
                p1[y * width + x] = x + y + i * 3;
            }
        }
        // Cb and Cr
        unsigned char* p2 = buffer.data + width * height;
        unsigned char* p3 = buffer.data + width * height + width * height / 4;
        for (auto y = 0; y < height / 2; ++y) {
            for (auto x = 0; x < width / 2; ++x) {
                p2[y * width / 2 + x] = 128 + y + i * 2;
                p3[y * width / 2 + x] = 64 + x + i * 5;
            }
        }
        packet_encode.pushScale(buffer);
        if (++i > 25) i = 0;
        std::this_thread::sleep_for(std::chrono::milliseconds(40));
    }
}

2.回調(diào)函數(shù)read_packet：avio_alloc_context中使用，不斷從隊(duì)列中獲取數(shù)據(jù)，av_read_frame中也會(huì)從這里獲取數(shù)據(jù)：每次從隊(duì)列中獲取一幀數(shù)據(jù)

int read_packet(void* opaque, uint8_t* buf, int buf_size)
{
    PacketScaleQueue* packet_encode = static_cast<PacketScaleQueue*>(opaque);
    Buffer buffer;
    packet_encode->popScale(buffer);
    memcpy(buf, buffer.data, buf_size);
    packet_encode->pushPacket(buffer);
    return buf_size;
}

3.函數(shù)get_input_format_context：創(chuàng)建輸入AVFormatContext，需要調(diào)用av_dict_set設(shè)置video_size和pixel_format

AVFormatContext* get_input_format_context(AVIOContext* avio_ctx)
{
    AVFormatContext* ifmt_ctx = avformat_alloc_context();
    if (!ifmt_ctx) {
        print_error_string(AVERROR(ENOMEM));
        return nullptr;
    }
    ifmt_ctx->pb = avio_ctx;
    AVDictionary* dict = nullptr;
    av_dict_set(&dict, "video_size", video_size, 0);
    av_dict_set(&dict, "pixel_format", pixel_format, 0);
    auto ret = avformat_open_input(&ifmt_ctx, nullptr, av_find_input_format("rawvideo"), &dict);
    if (ret < 0) {
        fprintf(stderr, "Could not open input\n");
        print_error_string(ret);
        return nullptr;
    }
    av_dict_free(&dict);
    ret = avformat_find_stream_info(ifmt_ctx, nullptr);
    if (ret < 0) {
        fprintf(stderr, "Could not find stream information\n");
        print_error_string(ret);
        return nullptr;
    }
    for (unsigned int i = 0; i < ifmt_ctx->nb_streams; ++i) {
        const AVStream* stream = ifmt_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, "error: no video stream\n");
        return nullptr;
    }
    if (ifmt_ctx->streams[video_stream_index]->codecpar->codec_id != AV_CODEC_ID_RAWVIDEO) {
        fprintf(stderr, "error: this test code only support rawvideo encode: %d\n", ifmt_ctx->streams[video_stream_index]->codecpar->codec_id);
        return nullptr;
    }
    av_dump_format(ifmt_ctx, 0, "nothing", 0);
    return ifmt_ctx;
}

4.函數(shù)get_decode_context：創(chuàng)建解碼AVCodecContext

AVCodecContext* get_decode_context(AVFormatContext* ifmt_ctx)
{
    AVCodec* decoder = nullptr;
    auto ret = av_find_best_stream(ifmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &decoder, 0);
    if (ret < 0) {
        fprintf(stderr, "fail to av_find_best_stream: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    AVCodecContext* dec_ctx = avcodec_alloc_context3(decoder);
    if (!dec_ctx) {
        fprintf(stderr, "fail to avcodec_alloc_context3\n");
        return nullptr;
    }
    ret = avcodec_parameters_to_context(dec_ctx, ifmt_ctx->streams[video_stream_index]->codecpar);
    if (ret < 0) {
        fprintf(stderr, "fail to avcodec_parameters_to_context: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    dec_ctx->framerate = av_guess_frame_rate(ifmt_ctx, ifmt_ctx->streams[video_stream_index], nullptr);
    ret = avcodec_open2(dec_ctx, decoder, nullptr);
    if (ret != 0) {
        fprintf(stderr, "fail to avcodec_open2: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    return dec_ctx;
}

5.函數(shù)get_encode_context：創(chuàng)建編碼AVCodecContext，注意對(duì)enc_ctx的相關(guān)成員的賦值

AVCodecContext* get_encode_context(AVFormatContext* ifmt_ctx)
{
    AVCodec* encodec = avcodec_find_encoder_by_name("mpeg1video"); // ffmpeg.exe -encoders
    if (!encodec) {
        fprintf(stderr, "fail to avcodec_find_encoder_by_name\n");
        return nullptr;
    }
    AVCodecContext* enc_ctx = avcodec_alloc_context3(encodec);
    if (!enc_ctx) {
        fprintf(stderr, "fail to avcodec_alloc_context3\n");
        return nullptr;
    }
    enc_ctx->bit_rate = 400000;
    enc_ctx->framerate = ifmt_ctx->streams[video_stream_index]->r_frame_rate;
    enc_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    enc_ctx->height = ifmt_ctx->streams[video_stream_index]->codecpar->height;
    enc_ctx->width = ifmt_ctx->streams[video_stream_index]->codecpar->width;
    enc_ctx->time_base = av_inv_q(av_d2q(frame_rate, 4096));
    enc_ctx->max_b_frames = 1;
    //if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER) // true
    enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    auto ret = avcodec_open2(enc_ctx, encodec, nullptr);
    if (ret != 0) {
        fprintf(stderr, "fail to avcodec_open2: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    return enc_ctx;
}

6.函數(shù)get_output_format_context：創(chuàng)建輸出AVFormatContext

AVFormatContext* get_output_format_context(const AVCodecContext* enc_ctx, const char* filename)
{
    AVFormatContext* ofmt_ctx = nullptr;
    auto ret = avformat_alloc_output_context2(&ofmt_ctx, nullptr, nullptr, filename);
    if (ret < 0 || !ofmt_ctx) {
        fprintf(stderr, "fail to avformat_alloc_output_context2: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    AVStream* out_stream = avformat_new_stream(ofmt_ctx, nullptr);
    if (!out_stream) {
        fprintf(stderr, "fail to avformat_new_stream\n");
        return nullptr;
    }
    ret = avcodec_parameters_from_context(out_stream->codecpar, enc_ctx);
    if (ret < 0) {
        fprintf(stderr, "fail to avcodec_parameters_from_context: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    out_stream->time_base = enc_ctx->time_base;
    if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE)) { // true
        ret = avio_open(&ofmt_ctx->pb, filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "fail to avio_open: %d\n", ret);
            print_error_string(ret);
            return nullptr;
        }
    }
    ret = avformat_write_header(ofmt_ctx, nullptr);
    if (ret < 0) {
        fprintf(stderr, "fail to avformat_write_header: %d\n", ret);
        print_error_string(ret);
        return nullptr;
    }
    av_dump_format(ofmt_ctx, 0, filename, 1);
    return ofmt_ctx;
}

7.函數(shù)decode: 注意對(duì)packet的判斷，它有可能為nullptr；調(diào)用一次avcodec_send_packet，可能需調(diào)用多次avcodec_receive_frame，因此需要將avcodec_receive_frame放在while中；需要對(duì)dec_ctx->time_base進(jìn)行設(shè)置

int decode(AVPacket* packet, AVFormatContext* ifmt_ctx, AVCodecContext* dec_ctx, AVFrame* frame)
{
    if (packet)
        av_packet_rescale_ts(packet, ifmt_ctx->streams[video_stream_index]->time_base, dec_ctx->time_base);
    auto ret = avcodec_send_packet(dec_ctx, packet);
    if (ret < 0) {
        fprintf(stderr, "fail to avcodec_send_packet: %d\n", ret);
        print_error_string(ret);
        return -1;
    }
    while (1) {
        ret = avcodec_receive_frame(dec_ctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) { // AVERROR(EAGAIN): decode is not yet complete
            //fprintf(stderr, "Warning: avcodec_receive_frame: %d\n", ret);
            //print_error_string(ret);
            break;
        }
        else if (ret < 0) {
            fprintf(stderr, "fail to avcodec_receive_frame: %d\n", ret);
            print_error_string(ret);
            return ret;
        }
        frame->pts = frame->best_effort_timestamp;
        break;
    }
    if (packet)
        av_packet_unref(packet);
    return 0;
}

8.函數(shù)encode：注意：調(diào)用一次avcodec_send_frame，可能需要調(diào)用多次avcodec_receive_packet，因此需要將avcodec_receive_packet放在while中；需要對(duì)ofmt_ctx->streams[0]->time_base進(jìn)行設(shè)置，否則生成的mp4中無(wú)法獲取幀速率；也可在調(diào)用avformat_write_header時(shí)設(shè)置video_track_timescale指定

int encode(AVCodecContext* enc_ctx, AVFrame* frame, AVPacket* packet, AVFormatContext* ifmt_ctx, AVFormatContext* ofmt_ctx)
{
    auto ret = avcodec_send_frame(enc_ctx, frame);
    if (ret < 0) {
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            fprintf(stderr, "Warning: avcodec_send_frame: %d\n", ret);
            print_error_string(ret);
            ret = 0;
        }
        else {
            fprintf(stderr, "fail to avcodec_send_frame: %d\n", ret);
            print_error_string(ret);
            return ret;
        }
    }
    while (1) {
        ret = avcodec_receive_packet(enc_ctx, packet);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) { // AVERROR(EAGAIN): encode is not yet complete
            //fprintf(stderr, "Warning: avcodec_receive_packet: %d\n", ret);
            //print_error_string(ret);
            break;
        }
        if (ret < 0) {
            fprintf(stderr, "fail to avcodec_receive_packet: %d\n", ret);
            print_error_string(ret);
            return ret;
        }
        packet->stream_index = 0;
        av_packet_rescale_ts(packet, ifmt_ctx->streams[video_stream_index]->time_base, ofmt_ctx->streams[0]->time_base);
        //packet2->pts = packet2->dts = frame->pts *
        //    ofmt_ctx->streams[0]->time_base.den / ofmt_ctx->streams[0]->time_base.num / 
        //    (enc_ctx->framerate.num / enc_ctx->framerate.den);
        ret = av_interleaved_write_frame(ofmt_ctx, packet);
        if (ret < 0) {
            print_error_string(ret);
            return ret;
        }
        av_packet_unref(packet);
    }
    return 0;
}

9.主函數(shù)test_ffmpeg_save_video_slice：注意：在退出前需要flush decoder和encoder；寫(xiě)入視頻文件需先調(diào)用avformat_write_header，然后持續(xù)調(diào)用av_interleaved_write_frame，退出前再需調(diào)用av_write_trailer；每次新文件的寫(xiě)入，需重新調(diào)用get_decode_context、get_encode_context、get_output_format_context并在之前作相應(yīng)free

int test_ffmpeg_save_video_slice()
{
    PacketScaleQueue packet_encode;
    packet_encode.init(queue_size, block_size);
    std::thread thread_packet(set_packet, std::ref(packet_encode));
    uint8_t* avio_ctx_buffer = static_cast<uint8_t*>(av_malloc(block_size));
    if (!avio_ctx_buffer) {
        print_error_string(AVERROR(ENOMEM));
        return -1;
    }
    AVIOContext* avio_ctx = avio_alloc_context(avio_ctx_buffer, block_size, 0, &packet_encode, &read_packet, nullptr, nullptr);
    if (!avio_ctx) {
        print_error_string(AVERROR(ENOMEM));
        return -1;
    }
    AVFormatContext* ifmt_ctx = get_input_format_context(avio_ctx);
    if (!ifmt_ctx) {
        fprintf(stderr, "fail to get_input_format_context\n");
        return -1;
    }
    AVPacket *packet = av_packet_alloc(), *packet2 = av_packet_alloc();
    if (!packet || !packet2) {
        fprintf(stderr, "fail to av_packet_alloc\n");
        return -1;
    }
    AVFrame* frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "fail to av_frame_alloc\n");
        return -1;
    }
    int count = 0, name = 1;
    AVCodecContext* enc_ctx = nullptr;
    AVFormatContext* ofmt_ctx = nullptr;
    AVCodecContext* dec_ctx = nullptr;
    while (1) {
        auto ret = av_read_frame(ifmt_ctx, packet);
        if (ret < 0) {
            break;
        }
        if (packet->stream_index != video_stream_index) {
            av_packet_unref(packet);
            continue;
        }
        if (count % slice_size == 0) {
            enc_ctx = get_encode_context(ifmt_ctx);
            if (!enc_ctx) {
                fprintf(stderr, "fail to avcodec_alloc_context3\n");
                return -1;
            }
            std::string filename = std::to_string(name) + ".mp4";
            filename = std::string(path) + filename;
            ofmt_ctx = get_output_format_context(enc_ctx, filename.c_str());
            if (!ofmt_ctx) {
                fprintf(stderr, "fail to get_output_format_context\n");
                return -1;
            }
            dec_ctx = get_decode_context(ifmt_ctx);
            if (!dec_ctx) {
                fprintf(stderr, "fail to get_decode_context\n");
                return -1;
            }
            ++name;
        }
        if (decode(packet, ifmt_ctx, dec_ctx, frame) != 0) return -1;
        if (encode(enc_ctx, frame, packet2, ifmt_ctx, ofmt_ctx) != 0) return -1;
        //fprintf(stdout, "count: %d\n", count);
        if (count + 1 == total_frames) { // terminate loop
            packet_encode_flag = false;
            // flush the decoder
            decode(nullptr, ifmt_ctx, dec_ctx, frame);
            if (frame->data[0])
                encode(enc_ctx, frame, packet2, ifmt_ctx, ofmt_ctx);
            // flush the encoder
            encode(enc_ctx, nullptr, packet2, ifmt_ctx, ofmt_ctx);
            av_write_trailer(ofmt_ctx);
            break;
        }
        ++count;
        if (count > 1 && count % slice_size == 0) {
            // flush the decoder
            decode(nullptr, ifmt_ctx, dec_ctx, frame);
            if (frame->data[0])
                encode(enc_ctx, frame, packet2, ifmt_ctx, ofmt_ctx);
            // flush the encoder
            encode(enc_ctx, nullptr, packet2, ifmt_ctx, ofmt_ctx);
            av_write_trailer(ofmt_ctx);
            avcodec_free_context(&dec_ctx);
            avcodec_free_context(&enc_ctx);
            avio_closep(&ofmt_ctx->pb);
            avformat_free_context(ofmt_ctx);
        }
    }
    av_packet_free(&packet);
    av_packet_free(&packet2);
    av_frame_free(&frame);
    avcodec_free_context(&dec_ctx);
    avcodec_free_context(&enc_ctx);
    avio_closep(&ofmt_ctx->pb);
    avformat_close_input(&ofmt_ctx);
    avformat_close_input(&ifmt_ctx);
    // note: the internal buffer could have changed, and be != avio_ctx_buffer
    if (avio_ctx) {
        av_freep(&avio_ctx->buffer);
        av_freep(&avio_ctx);
    }
    thread_packet.join();
    fprintf(stdout, "test finish\n");
    return 0;
}

執(zhí)行結(jié)果如下圖所示：

可調(diào)用ffprobe.exe驗(yàn)證每個(gè)生成的視頻文件的總幀數(shù)，如1.mp4,執(zhí)行如下命令：

ffprobe.exe -v error -select_streams v:0 -show_entries stream=nb_frames -of default=nokey=1:noprint_wrappers=1 1.mp4

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

到此這篇關(guān)于FFmpeg實(shí)現(xiàn)將編碼后數(shù)據(jù)保存成mp4的文章就介紹到這了,更多相關(guān)FFmpeg數(shù)據(jù)保存為mp4內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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