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：

#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\n");
            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\n");
            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.\n");

    if (!pps_seen)
        av_log(NULL, AV_LOG_WARNING,
            "Warning: PPS NALU missing or invalid. "
            "The resulting stream may not play.\n");

    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\n");
                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\n");
                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)\n",
                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!\n");
        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!\n");
        //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;
}