裁剪FFmpeg编译GIF编码Demo时链接错误的排查与解决

需求背景 #

我需要使用FFmpeg的GIF编码功能将ARGB图像编码为GIF，因为GIF库的编码效果不如FFmpeg。但avcodec等库体积过大，因此对FFmpeg进行裁剪，仅保留GIF编码功能。

FFmpeg裁剪配置脚本 #

#!/bin/sh
# ./configure --prefix=$(pwd)/output --arch=arm --target-os=linux --enable-cross-compile --disable-asm --cross-prefix=arm-linux-gnueabihf- 
./configure --prefix=$(pwd)/output --target-os=linux --disable-asm \
--disable-gpl --enable-nonfree --enable-error-resilience --enable-debug --enable-shared --enable-small --enable-zlib \
--disable-ffmpeg --disable-ffprobe --disable-ffplay --disable-programs --disable-symver\
 --disable-doc --disable-htmlpages --disable-manpages --disable-podpages --disable-decoder=h264 --enable-avformat \
 --disable-txtpages --enable-avcodec --enable-avutil \
 --disable-avresample --disable-avfilter --disable-avdevice --disable-postproc \
 --disable-swscale --enable-decoder=gif --enable-demuxer=gif --enable-muxer=gif --disable-iconv \
 --disable-v4l2-m2m --disable-indevs --disable-outdevs

make clean
make -j8

make install

GIF编码测试Demo代码 #

#include <stdio.h>
// #include "output/include/imgutils.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/avutil.h"

int main() {
    AVCodec *enc_codec;
    AVCodecContext *enc_ctx = NULL;
    AVStream *stream = NULL;
    int ret;

    AVFormatContext *fmt_ctx = avformat_alloc_context();
    if (!fmt_ctx) {
        fprintf(stderr, "Could not allocate format context\n");
        return 1;
    }
    
    AVInputFormat *input_fmt = av_find_input_format("image2");
    if ((ret = avformat_open_input(&fmt_ctx, "input.bmp", input_fmt, NULL)) < 0) {
        fprintf(stderr, "Could not open input file %d\n", ret);
        return ret;
    }

    AVCodec *dec_codec = avcodec_find_decoder(AV_CODEC_ID_BMP);
    if (!dec_codec) {
        fprintf(stderr, "Decoder not found\n");
        return 1;
    }
    
    AVCodecContext *dec_ctx = avcodec_alloc_context3(dec_codec);
    if (!dec_ctx) {
        fprintf(stderr, "Could not allocate decoder context\n");
        return 1;
    }

    if ((ret = avcodec_open2(dec_ctx, dec_codec, NULL)) < 0) {
        fprintf(stderr, "Could not open decoder\n");
        return 1;
    }

    AVOutputFormat *out_fmt = av_guess_format("gif", NULL, NULL);
    if (!out_fmt) {
        fprintf(stderr, "Could not find output format\n");
        return 1;
    }

    AVFormatContext *out_ctx = NULL;
    if ((ret = avformat_alloc_output_context2(&out_ctx, out_fmt, NULL, NULL)) < 0) {
        fprintf(stderr, "Could not allocate output context\n");
        return 1;
    }

    stream = avformat_new_stream(out_ctx, NULL);
    if (!stream) {
        fprintf(stderr, "Could not create new stream\n");
        return 1;
    }

    enc_codec = avcodec_find_encoder(AV_CODEC_ID_GIF);
    if (!enc_codec) {
        fprintf(stderr, "Encoder not found\n");
        return 1;
    }

    enc_ctx = avcodec_alloc_context3(enc_codec);
    if (!enc_ctx) {
        fprintf(stderr, "Could not allocate encoder context\n");
        return 1;
    }

    if ((ret = avcodec_parameters_from_context(stream->codecpar, dec_ctx)) < 0) {
        fprintf(stderr, "Could not copy decoder parameters\n");
        return 1;
    }

    if ((ret = avcodec_open2(enc_ctx, enc_codec, NULL)) < 0) {
        fprintf(stderr, "Could not open encoder\n");
        return 1;
    }
    
    enc_ctx->pix_fmt = AV_PIX_FMT_RGB8; 
    enc_ctx->width = dec_ctx->width; 
    enc_ctx->height = dec_ctx->height; 
    enc_ctx->time_base = (AVRational){1, 25}; 

    avformat_init_output(out_ctx, NULL);

    if (!(out_fmt->flags & AVFMT_NOFILE)) {
        if ((ret = avio_open(&out_ctx->pb, "output.gif", AVIO_FLAG_WRITE)) < 0) {
            fprintf(stderr, "Could not open output file\n");
            return ret;
        }
    }

    avformat_write_header(out_ctx, NULL);

    AVFrame *frame = av_frame_alloc();
    AVPacket pkt;
    int frame_count = 0;

    while (av_read_frame(fmt_ctx, &pkt) >= 0) {
        avcodec_send_packet(dec_ctx, &pkt);
        while (avcodec_receive_frame(dec_ctx, frame) == 0) {
            avcodec_send_frame(enc_ctx, frame);
            while (avcodec_receive_packet(enc_ctx, &pkt) == 0) {
                pkt.stream_index = stream->index;
                av_interleaved_write_frame(out_ctx, &pkt);
                av_packet_unref(&pkt);
            }

            frame_count++;
            printf("Encoded frame %d\n", frame_count);
        }
        av_packet_unref(&pkt);
    }

    av_write_trailer(out_ctx);

    avcodec_close(enc_ctx);
    avcodec_free_context(&enc_ctx);
    avcodec_close(dec_ctx);
    avcodec_free_context(&dec_ctx);
    av_frame_free(&frame);

    avformat_close_input(&fmt_ctx);
    avformat_free_context(fmt_ctx);
    avio_close(out_ctx->pb);
    avformat_free_context(out_ctx);

    return 0;
}

Demo编译脚本 #

#!/bin/sh
gcc -o x2gif x2gif.c -L ./output/lib/ -l:libavformat.a -l:libavcodec.a -l:libavutil.a -lz -I ./output/include/

编译错误信息 #

./output/lib/libavutil.a(lfg.o): In function `av_bmg_get':
/data1/yang/tool/ffmpeg-3.4.4/libavutil/lfg.c:59: undefined reference to `log'
./output/lib/libavutil.a(hwcontext_cuda.o): In function `cuda_free_functions':
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:175: undefined reference to `dlclose'
./output/lib/libavutil.a(hwcontext_cuda.o): In function `cuda_load_functions':
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:192: undefined reference to `dlopen'
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:194: undefined reference to `dlsym'
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:195: undefined reference to `dlsym'
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:196: undefined reference to `dlsym'
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:197: undefined reference to `dlsym'
/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:198: undefined reference to `dlsym'
./output/lib/libavutil.a(hwcontext_cuda.o):/data1/yang/tool/ffmpeg-3.4.4/./compat/cuda/dynlink_loader.h:199: more undefined references to `dlsym' follow
./output/lib/libavutil.a(rational.o): In function `av_d2q':
/data1/yang/tool/ffmpeg-3.4.4/libavutil/rational.c:120: undefined reference to `floor'
./output/lib/libavutil.a(eval.o): In function `eval_expr':
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:184: undefined reference to `exp'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:185: undefined reference to `exp'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:189: undefined reference to `floor'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:190: undefined reference to `ceil'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:191: undefined reference to `trunc'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:192: undefined reference to `round'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:263: undefined reference to `pow'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:300: undefined reference to `floor'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:309: undefined reference to `pow'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:315: undefined reference to `hypot'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:316: undefined reference to `atan2'
./output/lib/libavutil.a(eval.o): In function `ff_exp10':
/data1/yang/tool/ffmpeg-3.4.4/libavutil/ffmath.h:44: undefined reference to `exp2'
./output/lib/libavutil.a(eval.o): In function `parse_primary':
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:417: undefined reference to `sinh'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:418: undefined reference to `cosh'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:419: undefined reference to `tanh'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:420: undefined reference to `sin'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:421: undefined reference to `cos'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:422: undefined reference to `tan'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:423: undefined reference to `atan'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:424: undefined reference to `asin'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:425: undefined reference to `acos'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:426: undefined reference to `exp'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:427: undefined reference to `log'
/data1/yang/tool/ffmpeg-3.4.4/libavutil/eval.c:428: undefined reference to `fabs'

问题 #

如何排查并解决该编译链接错误？

内容的提问来源于stack exchange，提问作者yangjinhui2936