• FFmpeg开发实战(五):FFmpeg 抽取音视频的视频数据


     如何使用FFmpeg抽取音视频的视频数据,代码如下:

    // FFmpegTest.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
    //
    
    #include "pch.h"
    #include <iostream>
    #include "AACFormat.h"
    
    #define __STDC_CONSTANT_MACROS
    #define __STDC_FORMAT_MACROS
    
    // For extractVideo
    #ifndef AV_WB32
    #   define AV_WB32(p, val) do {                 
            uint32_t d = (val);                     
            ((uint8_t*)(p))[3] = (d);               
            ((uint8_t*)(p))[2] = (d)>>8;            
            ((uint8_t*)(p))[1] = (d)>>16;           
            ((uint8_t*)(p))[0] = (d)>>24;           
        } while(0)
    #endif
    
    // For extractVideo
    #ifndef AV_RB16
    #   define AV_RB16(x)                           
        ((((const uint8_t*)(x))[0] << 8) |          
          ((const uint8_t*)(x))[1])
    #endif
    
    
    extern "C"{
    #include <stdio.h>
    #include "libavcodec/avcodec.h"
    #include "libavformat/avformat.h"
    #include "libavutil/log.h"
    }
    
    // For extractVideo
    static int alloc_and_copy(AVPacket *out,
        const uint8_t *sps_pps, uint32_t sps_pps_size,
        const uint8_t *in, uint32_t in_size)
    {
        uint32_t offset = out->size;
        uint8_t nal_header_size = offset ? 3 : 4;
        int err;
    
        err = av_grow_packet(out, sps_pps_size + in_size + nal_header_size);
        if (err < 0)
            return err;
    
        if (sps_pps)
            memcpy(out->data + offset, sps_pps, sps_pps_size);
        memcpy(out->data + sps_pps_size + nal_header_size + offset, in, in_size);
        if (!offset) {
            AV_WB32(out->data + sps_pps_size, 1);
        }
        else {
            (out->data + offset + sps_pps_size)[0] =
                (out->data + offset + sps_pps_size)[1] = 0;
            (out->data + offset + sps_pps_size)[2] = 1;
        }
    
        return 0;
    }
    
    // For extractVideo
    int h264_extradata_to_annexb(const uint8_t *codec_extradata, const int codec_extradata_size, AVPacket *out_extradata, int padding)
    {
        uint16_t unit_size;
        uint64_t total_size = 0;
        uint8_t *out = NULL, unit_nb, sps_done = 0,
            sps_seen = 0, pps_seen = 0, sps_offset = 0, pps_offset = 0;
        const uint8_t *extradata = codec_extradata + 4;
        static const uint8_t nalu_header[4] = { 0, 0, 0, 1 };
        int length_size = (*extradata++ & 0x3) + 1; // retrieve length coded size, 用于指示表示编码数据长度所需字节数
    
        sps_offset = pps_offset = -1;
    
        /* retrieve sps and pps unit(s) */
        unit_nb = *extradata++ & 0x1f; /* number of sps unit(s) */
        if (!unit_nb) {
            goto pps;
        }
        else {
            sps_offset = 0;
            sps_seen = 1;
        }
    
        while (unit_nb--) {
            int err;
    
            unit_size = AV_RB16(extradata);
            total_size += unit_size + 4;
            if (total_size > INT_MAX - padding) {
                av_log(NULL, AV_LOG_ERROR,
                    "Too big extradata size, corrupted stream or invalid MP4/AVCC bitstream
    ");
                av_free(out);
                return AVERROR(EINVAL);
            }
            if (extradata + 2 + unit_size > codec_extradata + codec_extradata_size) {
                av_log(NULL, AV_LOG_ERROR, "Packet header is not contained in global extradata, "
                    "corrupted stream or invalid MP4/AVCC bitstream
    ");
                av_free(out);
                return AVERROR(EINVAL);
            }
            if ((err = av_reallocp(&out, total_size + padding)) < 0)
                return err;
            memcpy(out + total_size - unit_size - 4, nalu_header, 4);
            memcpy(out + total_size - unit_size, extradata + 2, unit_size);
            extradata += 2 + unit_size;
        pps:
            if (!unit_nb && !sps_done++) {
                unit_nb = *extradata++; /* number of pps unit(s) */
                if (unit_nb) {
                    pps_offset = total_size;
                    pps_seen = 1;
                }
            }
        }
    
        if (out)
            memset(out + total_size, 0, padding);
    
        if (!sps_seen)
            av_log(NULL, AV_LOG_WARNING,
                "Warning: SPS NALU missing or invalid. "
                "The resulting stream may not play.
    ");
    
        if (!pps_seen)
            av_log(NULL, AV_LOG_WARNING,
                "Warning: PPS NALU missing or invalid. "
                "The resulting stream may not play.
    ");
    
        out_extradata->data = out;
        out_extradata->size = total_size;
    
        return length_size;
    }
    
    // For extractVideo
    int h264_mp4toannexb(AVFormatContext *fmt_ctx, AVPacket *in, FILE *dst_fd)
    {
    
        AVPacket *out = NULL;
        AVPacket spspps_pkt;
    
        int len;
        uint8_t unit_type;
        int32_t nal_size;
        uint32_t cumul_size = 0;
        const uint8_t *buf;
        const uint8_t *buf_end;
        int            buf_size;
        int ret = 0, i;
    
        out = av_packet_alloc();
    
        buf = in->data;
        buf_size = in->size;
        buf_end = in->data + in->size;
    
        do {
            ret = AVERROR(EINVAL);
            if (buf + 4 /*s->length_size*/ > buf_end)
                goto fail;
    
            for (nal_size = 0, i = 0; i < 4/*s->length_size*/; i++)
                nal_size = (nal_size << 8) | buf[i];
    
            buf += 4; /*s->length_size;*/
            unit_type = *buf & 0x1f;
    
            if (nal_size > buf_end - buf || nal_size < 0)
                goto fail;
    
            /*
            if (unit_type == 7)
                s->idr_sps_seen = s->new_idr = 1;
            else if (unit_type == 8) {
                s->idr_pps_seen = s->new_idr = 1;
                */
                /* if SPS has not been seen yet, prepend the AVCC one to PPS */
                /*
                if (!s->idr_sps_seen) {
                    if (s->sps_offset == -1)
                        av_log(ctx, AV_LOG_WARNING, "SPS not present in the stream, nor in AVCC, stream may be unreadable
    ");
                    else {
                        if ((ret = alloc_and_copy(out,
                                             ctx->par_out->extradata + s->sps_offset,
                                             s->pps_offset != -1 ? s->pps_offset : ctx->par_out->extradata_size - s->sps_offset,
                                             buf, nal_size)) < 0)
                            goto fail;
                        s->idr_sps_seen = 1;
                        goto next_nal;
                    }
                }
            }
            */
    
            /* if this is a new IDR picture following an IDR picture, reset the idr flag.
             * Just check first_mb_in_slice to be 0 as this is the simplest solution.
             * This could be checking idr_pic_id instead, but would complexify the parsing. */
             /*
             if (!s->new_idr && unit_type == 5 && (buf[1] & 0x80))
                 s->new_idr = 1;
    
             */
             /* prepend only to the first type 5 NAL unit of an IDR picture, if no sps/pps are already present */
            if (/*s->new_idr && */unit_type == 5 /*&& !s->idr_sps_seen && !s->idr_pps_seen*/) {
    
                h264_extradata_to_annexb(fmt_ctx->streams[in->stream_index]->codec->extradata,
                    fmt_ctx->streams[in->stream_index]->codec->extradata_size,
                    &spspps_pkt,
                    AV_INPUT_BUFFER_PADDING_SIZE);
    
                if ((ret = alloc_and_copy(out,
                    spspps_pkt.data, spspps_pkt.size,
                    buf, nal_size)) < 0)
                    goto fail;
                /*s->new_idr = 0;*/
            /* if only SPS has been seen, also insert PPS */
            }
            /*else if (s->new_idr && unit_type == 5 && s->idr_sps_seen && !s->idr_pps_seen) {
                if (s->pps_offset == -1) {
                    av_log(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable
    ");
                    if ((ret = alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
                        goto fail;
                } else if ((ret = alloc_and_copy(out,
                                            ctx->par_out->extradata + s->pps_offset, ctx->par_out->extradata_size - s->pps_offset,
                                            buf, nal_size)) < 0)
                    goto fail;
            }*/ else {
                if ((ret = alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
                    goto fail;
                /*
                if (!s->new_idr && unit_type == 1) {
                    s->new_idr = 1;
                    s->idr_sps_seen = 0;
                    s->idr_pps_seen = 0;
                }
                */
            }
    
    
            len = fwrite(out->data, 1, out->size, dst_fd);
            if (len != out->size) {
                av_log(NULL, AV_LOG_DEBUG, "warning, length of writed data isn't equal pkt.size(%d, %d)
    ",
                    len,
                    out->size);
            }
            fflush(dst_fd);
    
        next_nal:
            buf += nal_size;
            cumul_size += nal_size + 4;//s->length_size;
        } while (cumul_size < buf_size);
    
        /*
        ret = av_packet_copy_props(out, in);
        if (ret < 0)
            goto fail;
    
        */
    fail:
        av_packet_free(&out);
    
        return ret;
    }
    
    
    // 使用FFmpeg从视频中抽取视频
    void extractVideo() {
    
        // Start Code 特征码
        // PSP PPS(从codec->extradata即在数据空间中存放)
    
        // 设置日志输出等级
        av_log_set_level(AV_LOG_INFO);
    
        AVFormatContext *fmt_ctx = NULL;
        AVPacket pkt;
    
        // 注册所有的格式和编解码器
        av_register_all();
    
        int ret;
        int len;
        int video_index = -1;
    
        // 打开输入文件
        ret = avformat_open_input(&fmt_ctx, "111.mp4", NULL, NULL);
    
        // 检查打开输入文件是否成功
        if (ret < 0) {
            printf("cant open file,error message = %s", av_err2str(ret));
            return;
        }
       // 打开输出文件
        FILE* dst_fd = fopen("111.H264", "wb");  // w 写入  b 二进制文件
    
        // 检查输出文件打开是否成功,如果失败,就输出日志,并关闭输出文件的引用
        if (!dst_fd) {
            av_log(NULL, AV_LOG_ERROR, "Can't Open Out File!
    ");
            avformat_close_input(&fmt_ctx);
        }
    
        av_init_packet(&pkt);
        pkt.data = NULL;
        pkt.size = 0;
    
        for (int i = 0; i < fmt_ctx->nb_streams; i++) {
            if (fmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
                video_index = i;
                break;
            }
        }
    
        printf("Video Stream Index = %d", video_index);
    
        // 检查发现视频流的结果
        if (video_index < 0) {
            av_log(NULL, AV_LOG_ERROR, "Can't find Best Video Stream!
    ");
            //printf("Reason = %s", av_err2str(ret));
            // 关闭输出文件和输出文件的引用
            avformat_close_input(&fmt_ctx);
            fclose(dst_fd);
            return;
        }
    
        while (av_read_frame(fmt_ctx, &pkt) >= 0) {
            if (pkt.stream_index == video_index) {
                h264_mp4toannexb(fmt_ctx, &pkt, dst_fd);
            }
            // 将引用基数减一
            av_packet_unref(&pkt);
        }
    
        // 关闭文件(输入/输出)
        avformat_close_input(&fmt_ctx);
        if (dst_fd) {
            fclose(dst_fd);
        }
    }
    
    int main(int argc, char* argv[]) {
        /**使用FFmpeg从视频中抽取视频 **/
        extractVideo();
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/renhui/p/10398293.html
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