C语言中使用FFmpeg读取视频文件后将音频流写入其他文件

1.输出为aac格式的音频流（写入成功，播放失败）

  1. 编写代码
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#include <stdio.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>

int main(int argc, char* argv[]) {
    if (argc < 3) {
        printf("Usage: %s <input_video> <output_audio>\n", argv[0]);
        return -1;
    }

    const char* input_file = argv[1];
    const char* output_file = argv[2];

    ///av_register_all();

    AVFormatContext* format_context = NULL;
    if (avformat_open_input(&format_context, input_file, NULL, NULL) != 0) {
        fprintf(stderr, "Could not open input file '%s'\n", input_file);
        return -1;
    }

    if (avformat_find_stream_info(format_context, NULL) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        avformat_close_input(&format_context);
        return -1;
    }

    AVStream* audio_stream = NULL;
    for (unsigned int i = 0; i < format_context->nb_streams; i++) {
        if (format_context->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            audio_stream = format_context->streams[i];
            break;
        }
    }

    if (!audio_stream) {
        fprintf(stderr, "Could not find audio stream\n");
        avformat_close_input(&format_context);
        return -1;
    }

    FILE* output_fp = fopen(output_file, "wb");
    if (!output_fp) {
        fprintf(stderr, "Could not open output file '%s'\n", output_file);
        avformat_close_input(&format_context);
        return -1;
    }

    AVPacket packet;
    while (av_read_frame(format_context, &packet) >= 0) {
        if (packet.stream_index == audio_stream->index) {
            fwrite(packet.data, 1, packet.size, output_fp);
        }
        av_packet_unref(&packet);
    }

    fclose(output_fp);
    avformat_close_input(&format_context);
    return 0;
}

  1. 运行

    1
    extract_audio input.mp4 output_audio.aac

2.输出为mp3

  1. 代码
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#include <stdio.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavutil/channel_layout.h>

int main(int argc, char* argv[]) {
    if (argc < 3) {
        printf("Usage: %s <input_video> <output_audio>\n", argv[0]);
        return -1;
    }

    const char* input_file = argv[1];
    const char* output_file = argv[2];

    // 检查输出文件扩展名
    const char* ext = strrchr(output_file, '.');
    if (!ext || (strcmp(ext, ".mp3") != 0)) {
        fprintf(stderr, "Output file must have .mp3 extension\n");
        return -1;
    }

    AVFormatContext* format_context = NULL;
    if (avformat_open_input(&format_context, input_file, NULL, NULL) != 0) {
        fprintf(stderr, "Could not open input file '%s'\n", input_file);
        return -1;
    }

    if (avformat_find_stream_info(format_context, NULL) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        avformat_close_input(&format_context);
        return -1;
    }

    AVStream* audio_stream = NULL;
    for (unsigned int i = 0; i < format_context->nb_streams; i++) {
        if (format_context->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            audio_stream = format_context->streams[i];
            break;
        }
    }

    if (!audio_stream) {
        fprintf(stderr, "Could not find audio stream\n");
        avformat_close_input(&format_context);
        return -1;
    }

    // 创建输出格式上下文，明确指定 MP3 格式
    AVFormatContext* output_format_context = NULL;
    avformat_alloc_output_context2(&output_format_context, NULL, "mp3", output_file);
    if (!output_format_context) {
        fprintf(stderr, "Could not create output context\n");
        avformat_close_input(&format_context);
        return -1;
    }

    AVStream* output_stream = avformat_new_stream(output_format_context, NULL);
    if (!output_stream) {
        fprintf(stderr, "Could not create output stream\n");
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 查找 MP3 编码器
    const AVCodec* mp3_codec = avcodec_find_encoder(AV_CODEC_ID_MP3);
    if (!mp3_codec) {
        fprintf(stderr, "Could not find MP3 encoder\n");
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    AVCodecContext* mp3_codec_context = avcodec_alloc_context3(mp3_codec);
    if (!mp3_codec_context) {
        fprintf(stderr, "Could not allocate MP3 codec context\n");
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 设置 MP3 编码参数
    mp3_codec_context->bit_rate = 128000;
    mp3_codec_context->sample_rate = audio_stream->codecpar->sample_rate;
    mp3_codec_context->sample_fmt = mp3_codec->sample_fmts[0];

    // 设置声道布局
    AVChannelLayout ch_layout = AV_CHANNEL_LAYOUT_STEREO;
    av_channel_layout_copy(&mp3_codec_context->ch_layout, &ch_layout);

    // 打开 MP3 编码器
    if (avcodec_open2(mp3_codec_context, mp3_codec, NULL) < 0) {
        fprintf(stderr, "Could not open MP3 codec\n");
        avcodec_free_context(&mp3_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 复制编码器参数到输出流
    if (avcodec_parameters_from_context(output_stream->codecpar, mp3_codec_context) < 0) {
        fprintf(stderr, "Could not copy codec parameters to output stream\n");
        avcodec_free_context(&mp3_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 打开输出文件
    if (avio_open(&output_format_context->pb, output_file, AVIO_FLAG_WRITE) < 0) {
        fprintf(stderr, "Could not open output file '%s'\n", output_file);
        avcodec_free_context(&mp3_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 写入文件头
    if (avformat_write_header(output_format_context, NULL) < 0) {
        fprintf(stderr, "Error occurred when writing header\n");
        avio_closep(&output_format_context->pb);
        avcodec_free_context(&mp3_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 解码和重编码音频数据
    AVPacket* packet = av_packet_alloc();
    AVFrame* frame = av_frame_alloc();
    AVPacket* out_packet = av_packet_alloc();

    // 打开输入解码器
    AVCodecContext* decoder_ctx = avcodec_alloc_context3(NULL);
    avcodec_parameters_to_context(decoder_ctx, audio_stream->codecpar);
    const AVCodec* decoder = avcodec_find_decoder(decoder_ctx->codec_id);
    avcodec_open2(decoder_ctx, decoder, NULL);

    while (av_read_frame(format_context, packet) >= 0) {
        if (packet->stream_index == audio_stream->index) {
            int ret = avcodec_send_packet(decoder_ctx, packet);
            if (ret < 0) {
                fprintf(stderr, "Error sending packet for decoding\n");
                continue;
            }

            while (ret >= 0) {
                ret = avcodec_receive_frame(decoder_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0) {
                    fprintf(stderr, "Error during decoding\n");
                    break;
                }

                // 发送帧到编码器
                ret = avcodec_send_frame(mp3_codec_context, frame);
                if (ret < 0) {
                    fprintf(stderr, "Error sending frame for encoding\n");
                    continue;
                }

                while (ret >= 0) {
                    ret = avcodec_receive_packet(mp3_codec_context, out_packet);
                    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                        break;
                    else if (ret < 0) {
                        fprintf(stderr, "Error during encoding\n");
                        break;
                    }

                    out_packet->stream_index = 0;
                    av_interleaved_write_frame(output_format_context, out_packet);
                    av_packet_unref(out_packet);
                }
            }
        }
        av_packet_unref(packet);
    }

    // 写入文件尾
    av_write_trailer(output_format_context);

    // 清理资源
    avcodec_free_context(&decoder_ctx);
    av_frame_free(&frame);
    av_packet_free(&packet);
    av_packet_free(&out_packet);
    avio_closep(&output_format_context->pb);
    avcodec_free_context(&mp3_codec_context);
    avformat_free_context(output_format_context);
    avformat_close_input(&format_context);

    return 0;
}

  1. 运行

    1
    extract_audio input.mp4 output_audio.mp3

3.修复噪音

  1. 代码
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#include <stdio.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/opt.h>
#include <libavutil/channel_layout.h>
#include <libswresample/swresample.h>

int main(int argc, char* argv[]) {
    if (argc < 3) {
        printf("Usage: %s <input_video> <output_audio>\n", argv[0]);
        return -1;
    }

    const char* input_file = argv[1];
    const char* output_file = argv[2];

    // 检查输出文件扩展名
    const char* ext = strrchr(output_file, '.');
    if (!ext || (strcmp(ext, ".mp3") != 0)) {
        fprintf(stderr, "Output file must have .mp3 extension\n");
        return -1;
    }

    AVFormatContext* format_context = NULL;
    if (avformat_open_input(&format_context, input_file, NULL, NULL) != 0) {
        fprintf(stderr, "Could not open input file '%s'\n", input_file);
        return -1;
    }

    if (avformat_find_stream_info(format_context, NULL) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        avformat_close_input(&format_context);
        return -1;
    }

    printf("Input file duration: %lld seconds\n", format_context->duration / AV_TIME_BASE);

    AVStream* audio_stream = NULL;
    int audio_stream_idx = -1;
    for (unsigned int i = 0; i < format_context->nb_streams; i++) {
        if (format_context->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            audio_stream = format_context->streams[i];
            audio_stream_idx = i;
            printf("Found audio stream at index %d\n", i);
            break;
        }
    }

    if (!audio_stream) {
        fprintf(stderr, "Could not find audio stream\n");
        avformat_close_input(&format_context);
        return -1;
    }

    printf("Audio Stream Info:\n");
    printf("Codec ID: %d\n", audio_stream->codecpar->codec_id);
    printf("Sample Rate: %d\n", audio_stream->codecpar->sample_rate);
    printf("Channels: %d\n", audio_stream->codecpar->ch_layout.nb_channels);

    AVFormatContext* output_format_context = NULL;
    avformat_alloc_output_context2(&output_format_context, NULL, "mp3", output_file);
    if (!output_format_context) {
        fprintf(stderr, "Could not create output context\n");
        avformat_close_input(&format_context);
        return -1;
    }

    AVStream* output_stream = avformat_new_stream(output_format_context, NULL);
    if (!output_stream) {
        fprintf(stderr, "Could not create output stream\n");
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 查找解码器
    const AVCodec* input_codec = avcodec_find_decoder(audio_stream->codecpar->codec_id);
    if (!input_codec) {
        fprintf(stderr, "Could not find input codec\n");
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    AVCodecContext* input_codec_context = avcodec_alloc_context3(input_codec);
    if (!input_codec_context) {
        fprintf(stderr, "Could not allocate input codec context\n");
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    if (avcodec_parameters_to_context(input_codec_context, audio_stream->codecpar) < 0) {
        fprintf(stderr, "Could not copy codec params to input codec context\n");
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    if (avcodec_open2(input_codec_context, input_codec, NULL) < 0) {
        fprintf(stderr, "Could not open input codec\n");
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    const AVCodec* output_codec = avcodec_find_encoder(AV_CODEC_ID_MP3);
    if (!output_codec) {
        fprintf(stderr, "Could not find MP3 encoder\n");
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    AVCodecContext* output_codec_context = avcodec_alloc_context3(output_codec);
    if (!output_codec_context) {
        fprintf(stderr, "Could not allocate output codec context\n");
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 设置输出编码器参数
    output_codec_context->bit_rate = 192000;
    output_codec_context->sample_rate = input_codec_context->sample_rate;
    output_codec_context->sample_fmt = output_codec->sample_fmts[0];

    // 设置声道布局
    AVChannelLayout stereo = AV_CHANNEL_LAYOUT_STEREO;
    av_channel_layout_copy(&output_codec_context->ch_layout, &stereo);

    if (avcodec_open2(output_codec_context, output_codec, NULL) < 0) {
        fprintf(stderr, "Could not open output codec\n");
        avcodec_free_context(&output_codec_context);
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    if (avcodec_parameters_from_context(output_stream->codecpar, output_codec_context) < 0) {
        fprintf(stderr, "Could not copy codec params to output stream\n");
        avcodec_free_context(&output_codec_context);
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 创建重采样上下文
    SwrContext* swr_ctx = swr_alloc();
    if (!swr_ctx) {
        fprintf(stderr, "Could not allocate resampler context\n");
        avcodec_free_context(&output_codec_context);
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    // 设置重采样参数
    av_opt_set_chlayout(swr_ctx, "in_chlayout", &input_codec_context->ch_layout, 0);
    av_opt_set_chlayout(swr_ctx, "out_chlayout", &output_codec_context->ch_layout, 0);
    av_opt_set_int(swr_ctx, "in_sample_rate", input_codec_context->sample_rate, 0);
    av_opt_set_int(swr_ctx, "out_sample_rate", output_codec_context->sample_rate, 0);
    av_opt_set_sample_fmt(swr_ctx, "in_sample_fmt", input_codec_context->sample_fmt, 0);
    av_opt_set_sample_fmt(swr_ctx, "out_sample_fmt", output_codec_context->sample_fmt, 0);

    if (swr_init(swr_ctx) < 0) {
        fprintf(stderr, "Could not initialize resampler\n");
        swr_free(&swr_ctx);
        avcodec_free_context(&output_codec_context);
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    if (!(output_format_context->oformat->flags & AVFMT_NOFILE)) {
        if (avio_open(&output_format_context->pb, output_file, AVIO_FLAG_WRITE) < 0) {
            fprintf(stderr, "Could not open output file\n");
            swr_free(&swr_ctx);
            avcodec_free_context(&output_codec_context);
            avcodec_free_context(&input_codec_context);
            avformat_free_context(output_format_context);
            avformat_close_input(&format_context);
            return -1;
        }
    }

    if (avformat_write_header(output_format_context, NULL) < 0) {
        fprintf(stderr, "Could not write header\n");
        avio_closep(&output_format_context->pb);
        swr_free(&swr_ctx);
        avcodec_free_context(&output_codec_context);
        avcodec_free_context(&input_codec_context);
        avformat_free_context(output_format_context);
        avformat_close_input(&format_context);
        return -1;
    }

    AVPacket* input_packet = av_packet_alloc();
    AVFrame* input_frame = av_frame_alloc();
    AVFrame* output_frame = av_frame_alloc();
    AVPacket* output_packet = av_packet_alloc();

    int64_t total_samples = 0;

    while (av_read_frame(format_context, input_packet) >= 0) {
        if (input_packet->stream_index == audio_stream_idx) {
            if (avcodec_send_packet(input_codec_context, input_packet) < 0) {
                fprintf(stderr, "Error sending packet for decoding\n");
                continue;
            }

            while (avcodec_receive_frame(input_codec_context, input_frame) >= 0) {
                output_frame->nb_samples = av_rescale_rnd(
                    swr_get_delay(swr_ctx, input_frame->sample_rate) + input_frame->nb_samples,
                    output_codec_context->sample_rate,
                    input_frame->sample_rate,
                    AV_ROUND_UP
                );

                output_frame->format = output_codec_context->sample_fmt;
                output_frame->sample_rate = output_codec_context->sample_rate;
                av_channel_layout_copy(&output_frame->ch_layout, &output_codec_context->ch_layout);

                if (av_frame_get_buffer(output_frame, 0) < 0) {
                    fprintf(stderr, "Could not allocate output frame samples\n");
                    continue;
                }

                if (swr_convert(swr_ctx,
                    output_frame->data,
                    output_frame->nb_samples,
                    (const uint8_t**)input_frame->data,
                    input_frame->nb_samples) < 0) {
                    fprintf(stderr, "Error while converting\n");
                    continue;
                }

                total_samples += output_frame->nb_samples;
                printf("Processing samples: %d\n", output_frame->nb_samples);

                if (avcodec_send_frame(output_codec_context, output_frame) < 0) {
                    fprintf(stderr, "Error sending frame for encoding\n");
                    continue;
                }

                while (avcodec_receive_packet(output_codec_context, output_packet) >= 0) {
                    printf("Writing packet of size: %d\n", output_packet->size);
                    if (av_interleaved_write_frame(output_format_context, output_packet) < 0) {
                        fprintf(stderr, "Error writing packet\n");
                    }
                    av_packet_unref(output_packet);
                }
                av_frame_unref(output_frame);
            }
            av_frame_unref(input_frame);
        }
        av_packet_unref(input_packet);
    }

    printf("Total processed samples: %lld\n", total_samples);

    // Flush encoder
    avcodec_send_frame(output_codec_context, NULL);
    while (avcodec_receive_packet(output_codec_context, output_packet) >= 0) {
        printf("Writing final packet of size: %d\n", output_packet->size);
        av_interleaved_write_frame(output_format_context, output_packet);
        av_packet_unref(output_packet);
    }

    av_write_trailer(output_format_context);

    av_packet_free(&input_packet);
    av_packet_free(&output_packet);
    av_frame_free(&input_frame);
    av_frame_free(&output_frame);
    swr_free(&swr_ctx);
    avcodec_free_context(&output_codec_context);
    avcodec_free_context(&input_codec_context);
    avio_closep(&output_format_context->pb);
    avformat_free_context(output_format_context);
    avformat_close_input(&format_context);

    return 0;
}

  1. 运行

    1
    extract_audio input.mp4 output_audio.mp3