ffmpeg+sdl2实现带音量柱的播放器

你可以使用FFmpeg和SDL2库来实现带有音量柱的播放器。下面是一个简单的示例代码，可以帮助你开始：

#include <stdio.h>
#include <SDL2/SDL.h>
#include <libavformat/avformat.h>
#include <libswresample/swresample.h>

#define SAMPLE_RATE 44100
#define CHANNELS 2
#define BUFFER_SIZE 4096

int main(int argc, char *argv[]) {
    if (argc < 2) {
        printf("Usage: %s <input_file>\n", argv[0]);
        return -1;
    }

    const char *inputFile = argv[1];

    // 初始化SDL
    if (SDL_Init(SDL_INIT_AUDIO) < 0) {
        printf("SDL initialization failed: %s\n", SDL_GetError());
        return -1;
    }

    // 打开输入文件
    AVFormatContext *formatContext = NULL;
    if (avformat_open_input(&formatContext, inputFile, NULL, NULL) != 0) {
        printf("Failed to open input file\n");
        return -1;
    }

    // 查找音频流信息
    if (avformat_find_stream_info(formatContext, NULL) < 0) {
        printf("Failed to find stream information\n");
        return -1;
    }

    // 查找音频流索引
    int audioStreamIndex = -1;
    for (int i = 0; i < formatContext->nb_streams; i++) {
        if (formatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            audioStreamIndex = i;
            break;
        }
    }

    if (audioStreamIndex == -1) {
        printf("Failed to find audio stream\n");
        return -1;
    }

    // 获取音频流解码参数
    AVCodecParameters *codecParams = formatContext->streams[audioStreamIndex]->codecpar;

    // 查找音频解码器
    AVCodec *codec = avcodec_find_decoder(codecParams->codec_id);
    if (codec == NULL) {
        printf("Failed to find decoder\n");
        return -1;
    }

    // 创建解码器上下文
    AVCodecContext *codecContext = avcodec_alloc_context3(codec);
    if (avcodec_parameters_to_context(codecContext, codecParams) != 0) {
        printf("Failed to copy decoder parameters to context\n");
        return -1;
    }

    // 打开解码器
    if (avcodec_open2(codecContext, codec, NULL) != 0) {
        printf("Failed to open decoder\n");
        return -1;
    }

    // 创建音频重采样上下文
    SwrContext *swrContext = swr_alloc();
    av_opt_set_int(swrContext, "in_channel_layout", codecContext->channel_layout, 0);
    av_opt_set_int(swrContext, "out_channel_layout", codecContext->channel_layout, 0);
    av_opt_set_int(swrContext, "in_sample_rate", codecContext->sample_rate, 0);
    av_opt_set_int(swrContext, "out_sample_rate", SAMPLE_RATE, 0);
    av_opt_set_sample_fmt(swrContext, "in_sample_fmt", codecContext->sample_fmt, 0);
    av_opt_set_sample_fmt(swrContext, "out_sample_fmt", AV_SAMPLE_FMT_S16, 0);
    swr_init(swrContext);

    // 设置SDL音频参数
    SDL_AudioSpec audioSpec;
    audioSpec.freq = SAMPLE_RATE;
    audioSpec.format = AUDIO_S16SYS;
    audioSpec.channels = CHANNELS;
    audioSpec.silence = 0;
    audioSpec.samples = BUFFER_SIZE;
    audioSpec.callback = NULL; // TODO: 实现音频回调函数
    audioSpec.userdata = codecContext;

    // 打开音频设备
    if (SDL_OpenAudio(&audioSpec, NULL) < 0) {
        printf("Failed to open audio device: %s\n", SDL_GetError());
        return -1;
    }

    // 开始播放
    SDL_PauseAudio(0);

    // 解码并播放音频数据
    AVPacket packet;
    av_init_packet(&packet);
    AVFrame *frame = av_frame_alloc();
    uint8_t *buffer = (uint8_t *) av_malloc(MAX_AUDIO_FRAME_SIZE);

    while (av_read_frame(formatContext, &packet) >= 0) {
        if (packet.stream_index == audioStreamIndex) {
            int ret = avcodec_send_packet(codecContext, &packet);
            if (ret < 0) {
                printf("Error sending a packet for decoding\n");
                break;
            }

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

                // 音频重采样
                int dstNbSamples = av_rescale_rnd(swr_get_delay(swrContext, frame->sample_rate) + frame->nb_samples,
                                                  SAMPLE_RATE, frame->sample_rate, AV_ROUND_UP);
                int nb = swr_convert(swrContext, &buffer, dstNbSamples, (const uint8_t **) frame->data, frame->nb_samples);
                int audioSize = nb * CHANNELS * av_get_bytes_per_sample(AV_SAMPLE_FMT_S16);

                // TODO: 更新音量柱

                // 播放音频数据
                SDL_QueueAudio(1, buffer, audioSize);
            }
        }

        av_packet_unref(&packet);
    }

    // 清理资源
    av_frame_free(&frame);
    av_free(buffer);
    swr_free(&swrContext);
    avcodec_close(codecContext);
    avformat_close_input(&formatContext);
    SDL_CloseAudio();
    SDL_Quit();

    return 0;
}

这只是一个简单的示例代码，你可能需要根据你的需求进行修改和扩展。要实现音量柱功能，你可以在音频回调函数中计算音频样本的能量，并将其映射到柱状图上。希望这对你有所帮助！