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Linux下使用ffmpeg播放mp3/aac/wav文件的音乐播放器应用

星夢妙者
发布: 2025-04-19 20:13:51
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196人浏览过

使用ffmpeg实现一个播放器的想法虽然不新颖,但在嵌入式linux上通过ffmpeg的代码接口实现,并使用alsa接口输出音频,还是有一定挑战和趣味性的。以下是对原文的伪原创处理:


实现一个嵌入式Linux上的音频播放器,支持mp3、aac和wav格式的文件,是一个有趣的项目。基于ffmpeg的强大功能,我们可以实现这个播放器,主要利用ffmpeg的协议处理和音频解码能力。尽管网上有很多相关代码,但由于版本差异,接口存在变化,实际实现时仍需花费不少时间调试。

总结几点关键经验:

  • 多参考官方示例程序,路径为ffmpeg-4.1.9/tmp/share/ffmpeg/examples。
  • avcodec_open2函数调用失败时,需使用avcodec_parameters_to_context函数将找到的音频解码器复制到解码器上下文中。
  • av_read_frame函数可能会导致内存泄漏,应使用av_packet_unref(&input_packet)函数释放内存。
  • 要枚举ALSA播放设备,可使用snd_device_name_get_hint函数。
  • avcodec_receive_frame函数接收解码后的帧,只需申请一次内存,AVFrame *pframeSRC = av_frame_alloc()。

使用的是ffmpeg-4.1.9版本,编译选项如下:

//fdk-aac
root@lyz-VirtualBox:/home/lyz/work/broadcast_app/app/thirds_libs_src/fdk-aac/build# vim arm-gcc-cxx11.cmake
root@lyz-VirtualBox:/home/lyz/work/broadcast_app/app/thirds_libs_src/fdk-aac/build# cmake -DCMAKE_TOOLCHAIN_FILE=/home/lyz/work/broadcast_app/app/thirds_libs_src/fdk-aac/build/arm-gcc-cxx11.cmake ../
-- The C compiler identification is GNU 6.4.1
root@lyz-VirtualBox:/home/lyz/work/broadcast_app/app_linux# cat /home/lyz/work/broadcast_app/app/thirds_libs_src/fdk-aac/build/arm-gcc-cxx11.cmake
# Sample toolchain file for building with gcc compiler
# Typical usage:
#    *) cmake -H. -B_build -DCMAKE_TOOLCHAIN_FILE="${PWD}/toolchains/gcc.cmake"
SET(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)
# set compiler
set(CMAKE_C_COMPILER arm-openwrt-linux-gnueabi-gcc)
set(CMAKE_CXX_COMPILER arm-openwrt-linux-gnueabi-g++)
set(CONFIGURE_OPTS --enable-static=yes --enable-shared=no --disable-shared)
# set c++ standard
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)
//mp3
/home/lyz/work/broadcast_app/app/thirds_libs_src/lame-3.100
./configure --host=arm-openwrt-linux-gnueabi --prefix=${PWD}/build/
./configure --target-os=linux --prefix=/home/lyz/work/broadcast_app/app_linux/thirds_libs_src/ffmpeg-4.1.9/tmp --disable-shared --disable-muxers --enable-pic --enable-static --enable-gpl --enable-nonfree --enable-ffmpeg --disable-debug --disable-filters --disable-encoders --disable-hwaccels --enable-static --enable-libmp3lame --enable-demuxers --enable-parsers --enable-protocols --disable-x86asm --disable-stripping --extra-cflags='-I/home/lyz/work/broadcast_app/app_linux/libs/include/ -I/home/lyz/work/broadcast_app/app_linux/libs/include/lame -Os -fpic ' --extra-ldflags='-ldl -lm -L/home/lyz/work/broadcast_app/app_linux/libs/' --enable-decoder=aac --enable-swresample --enable-decoder=ac3
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在cpp文件中引用ffmpeg库时,如果出现链接错误,需要在头文件包含处添加两个前缀:

//.cpp
#include <alsa>
#ifdef __cplusplus
extern "C" {
#endif
#include "libavutil/time.h"
#include "libavformat/avformat.h"
#include "libavcodec/avcodec.h"
#include "libavdevice/avdevice.h"
#include "libswresample/swresample.h"
#include "libswscale/swscale.h"
#ifdef __cplusplus
}
#endif
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即使修改了头文件包含方式,仍然可能出现链接错误,这与链接库的顺序有关。错误的库链接顺序如下:

LDFLAGS +=  -L ./libs/  -lavcodec -lavfilter -lavformat -lavutil -lpostproc -lswscale -lswresample  -lfdk-aac -lmp3lame
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正确的库链接顺序应为:

LDFLAGS += -Wl,-Bstatic -L./libs -lavformat -lavcodec -lswscale -lswresample -lavutil -lavfilter -lavdevice -lpostproc -lfdk-aac -lmp3lame
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注意动态链接和静态链接的区别

LDFLAGS += -Wl,-Bstatic -L./libs -lavformat -lavcodec -lswscale -lswresample -lavutil -lavfilter -lavdevice -lpostproc -lfdk-aac -lmp3lame
LDFLAGS += -Wl,-Bdynamic -ldl -lm -lasound -lpthread
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在处理内存泄漏问题时,可以使用valgrind工具进行检测:

root@lyz-VirtualBox:/home/lyz/work/broadcast_app/app_linux# valgrind ./bas ./Test1.wav 0
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最后,使用ALSA接口完整播放mp3文件声音的代码如下:

//static const char *device = "hw:1,0"; /* playback device "hw:0,0" */
static snd_pcm_format_t format = SND_PCM_FORMAT_S16; /* sample format */
static unsigned int rate = 44100; /* stream rate */
static unsigned int channels = 2; /* count of channels */
static unsigned int buffer_time = 500000; /* ring buffer length in us */
static unsigned int period_time = 100000; /* period time in us */
static int resample = 1; /* enable alsa-lib resampling */
static snd_pcm_sframes_t buffer_size;
static snd_pcm_sframes_t period_size;
snd_pcm_access_t mode = SND_PCM_ACCESS_RW_INTERLEAVED;
static snd_output_t *output = NULL;
/*配置参数*/
static int set_hwparams(snd_pcm_t *handle,snd_pcm_hw_params_t *params,snd_pcm_access_t access){
unsigned int rrate;
snd_pcm_uframes_t size;
int err, dir = 0;
/* choose all parameters */
err = snd_pcm_hw_params_any(handle, params);
if (err < 0) {
    printf("Broken configuration for playback: no configurations available: %s\n", snd_strerror(err));
    return err;
}
/* set hardware resampling */
err = snd_pcm_hw_params_set_rate_resample(handle, params, resample);
if (err < 0) {
    printf("Resampling setup failed for playback: %s\n", snd_strerror(err));
    return err;
}
/* set the interleaved read/write format */
err = snd_pcm_hw_params_set_access(handle, params, access);
if (err < 0) {
    printf("Access type not available for playback: %s\n", snd_strerror(err));
    return err;
}
/* set the sample format */
err = snd_pcm_hw_params_set_format(handle, params, format);
if (err < 0) {
    printf("Sample format not available for playback: %s\n", snd_strerror(err));
    return err;
}
/* set the count of channels */
err = snd_pcm_hw_params_set_channels(handle, params, channels);
if (err < 0) {
    printf("Channels count (%i) not available for playbacks: %s\n", channels, snd_strerror(err));
    return err;
}
/* set the stream rate */
rrate = rate;
err = snd_pcm_hw_params_set_rate_near(handle, params, &rrate, 0);
if (err < 0) {
    printf("Rate %iHz not available for playback: %s\n", rate, snd_strerror(err));
    return err;
}
if (rrate != rate) {
    printf("Rate doesn't match (requested %iHz, get %iHz)\n", rate, err);
    return -EINVAL;
}
/* set the buffer time */
err = snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, &dir);
if (err < 0) {
    printf("Unable to set buffer time %i for playback: %s\n", buffer_time, snd_strerror(err));
    return err;
}
err = snd_pcm_hw_params_get_buffer_size(params, &buffer_size);
if (err < 0) {
    printf("Unable to get buffer size for playback: %s\n", snd_strerror(err));
    return err;
}
printf("buffer_size = %ld\n", buffer_size);
/* set the period time */
err = snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, &dir);
if (err < 0) {
    printf("Unable to set period time %i for playback: %s\n", period_time, snd_strerror(err));
    return err;
}
err = snd_pcm_hw_params_get_period_size(params, &period_size, &dir);
if (err < 0) {
    printf("Unable to get period size for playback: %s\n", snd_strerror(err));
    return err;
}
printf("period_size = %ld\n", period_size);
/* write the parameters to the driver */
err = snd_pcm_hw_params(handle, params);
if (err < 0) {
    printf("Unable to set hw params for playback: %s\n", snd_strerror(err));
    return err;
}
return 0;
}
int test_play_mp3(int argc, char *argv[]){
int rc;
int size;
int got_picture;
int nb_data;
bool pkt_pending = false;
int audio_stream_idx;
char **hints, **n;
char *alsa_device_name;
if (argc < 2) {
    printf("Usage: %s <file>\n", argv[0]);
    return 1;
}
AVFormatContext *infmt_ctx = NULL;
AVPacket *input_packet = av_packet_alloc();
AVFrame *pframeSRC = av_frame_alloc();
AVFrame *pframePCM = av_frame_alloc();
int ret;
if ((ret = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
    printf("Playback open error: %s\n", snd_strerror(ret));
    return ret;
}
if ((err = snd_pcm_hw_params_malloc(&params)) < 0) {
    printf("Cannot allocate hardware parameter structure (%s)\n", snd_strerror(err));
    return err;
}
if ((err = set_hwparams(handle, params, mode)) < 0) {
    printf("Setting of hwparams failed: %s\n", snd_strerror(err));
    snd_pcm_hw_params_free(params);
    snd_pcm_close(handle);
    return err;
}
if ((err = snd_pcm_sw_params_malloc(&swparams)) < 0) {
    printf("Cannot allocate software parameters structure (%s)\n", snd_strerror(err));
    return err;
}
if ((err = set_swparams(handle, swparams)) < 0) {
    printf("Setting of swparams failed: %s\n", snd_strerror(err));
    snd_pcm_sw_params_free(swparams);
    snd_pcm_hw_params_free(params);
    snd_pcm_close(handle);
    return err;
}
if ((err = snd_pcm_prepare(handle)) < 0) {
    printf("Cannot prepare audio interface for use (%s)\n", snd_strerror(err));
    return err;
}
printf("Try to open the device for playback - success\r\n");
snd_pcm_close (pcm);
pcm = NULL;
alsa_device_name = name;
break;
}
printf("found device:%s\r\n", alsa_device_name);
//break;
}}
n++;
}
printf("Playback device is %s\n", alsa_device_name);
/* Install error handler after enumeration, otherwise we'll get many
* error messages about invalid card/device ID.
*/
snd_lib_error_set_handler(alsa_error_handler);
err = snd_device_name_free_hint((void**)hints);
err = snd_output_stdio_attach(&output, stdout, 0);
if (err < 0) {
    printf("Attach output failed: %s\n", snd_strerror(err));
    return err;
}
if ((ret = avformat_open_input(&infmt_ctx, argv[1], NULL, NULL)) < 0) {
    fprintf(stderr, "Could not open input file '%s' (error '%s')\n", argv[1], av_err2str(ret));
    return ret;
}
infmt_ctx->max_analyze_duration = 5*AV_TIME_BASE;
//读取一部分视音频流并且获得一些相关的信息
ret=avformat_find_stream_info(infmt_ctx, NULL);
if (ret < 0) {
    fprintf(stderr, "Could not find stream information\n");
    avformat_close_input(&infmt_ctx);
    return ret;
}
audio_stream_idx = av_find_best_stream(infmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
if (audio_stream_idx < 0) {
    fprintf(stderr, "Could not find any audio stream in the file\n");
    avformat_close_input(&infmt_ctx);
    return -1;
}
AVCodecParameters *pCodecParameters = infmt_ctx->streams[audio_stream_idx]->codecpar;
if (pCodecParameters == NULL){
    printf("pCodecParameters is NULL\n");
    avformat_close_input(&infmt_ctx);
    return -1;
}
//找到解码器
const AVCodec* decodec = avcodec_find_decoder(pCodecParameters->codec_id);
if (!decodec) {
    printf("not find decoder codec audio_stream_idx:%d codec_id:%d\n", audio_stream_idx, pCodecParameters->codec_id);
    avformat_close_input(&infmt_ctx);
    return -1;
}
AVCodecContext *decodec_ctx = avcodec_alloc_context3(decodec);
if (!decodec_ctx) {
    printf("Can't allocate decoder context\n");
    avformat_close_input(&infmt_ctx);
    return AVERROR(ENOMEM);
}
if(avcodec_parameters_to_context(decodec_ctx, pCodecParameters) < 0) {
    printf("Could not copy codec parameters to context\n");
    avcodec_free_context(&decodec_ctx);
    avformat_close_input(&infmt_ctx);
    return -1;
}
pkt_timebase = infmt_ctx->streams[audio_stream_idx]->time_base;
#if 0
decodec_ctx->sample_rate = pCodecParameters->sample_rate;
decodec_ctx->sample_fmt = (AVSampleFormat)pCodecParameters->format   ;
decodec_ctx->channels = pCodecParameters->channels;
decodec_ctx->channel_layout = pCodecParameters->channel_layout;
#endif
//打开解码器
ret = avcodec_open2(decodec_ctx, decodec, NULL);
if (ret < 0) {
    printf("Could not open codec\n");
    avcodec_free_context(&decodec_ctx);
    avformat_close_input(&infmt_ctx);
    return ret;
}
pframePCM->format = AV_SAMPLE_FMT_S16;
pframePCM->channel_layout = AV_CH_LAYOUT_STEREO;
pframePCM->sample_rate = rate;
pframePCM->nb_samples = period_size;
pframePCM->channels = channels;
av_frame_get_buffer(pframePCM, 0);
#else
uint8_t *converted_input_samples = NULL;
int converted_input_samples_size = av_samples_alloc(&converted_input_samples, NULL,  channels ,  period_size,  AV_SAMPLE_FMT_S16, 0);
#endif
struct SwrContext *pcm_convert_ctx  = swr_alloc();
if (!pcm_convert_ctx) {
    printf("Could not allocate resampler context\n");
    free(buffer);
    return -1;
}
swr_alloc_set_opts(pcm_convert_ctx,
                   AV_CH_LAYOUT_STEREO,
                   AV_SAMPLE_FMT_S16,
                   pframePCM->sample_rate,
    av_get_default_channel_layout(decodec_ctx->channels),
                   decodec_ctx->sample_fmt,
                  decodec_ctx->sample_rate,
                   0,
                   NULL);
ret = swr_init(pcm_convert_ctx);
if (ret < 0) {
    printf("Could not open resampler context\n");
    swr_free(&pcm_convert_ctx);
    free(buffer);
    return -1;
}
pframeSRC->format = (AVSampleFormat)pCodecParameters->format   ;
pframeSRC->channel_layout = decodec_ctx->channel_layout;
pframeSRC->sample_rate = decodec_ctx->sample_rate;
pframeSRC->nb_samples =  (20*decodec_ctx->sample_rate * channels * 2) / 8000;;
pframeSRC->channels = channels;
av_frame_get_buffer(pframeSRC, 0);
#endif
int finished = 0;
int decode_ret = 0;
int data_size = av_get_bytes_per_sample(decodec_ctx->sample_fmt);
printf("data_size:%d,  frame_size:%d, dst_samples:%d\n", data_size,  pCodecParameters->frame_size, pframePCM->nb_samples);
while (!finished) {
ret=av_read_frame(infmt_ctx, input_packet);
if (ret != 0) {
    if (ret == AVERROR_EOF){
       finished = 1;
       break;
    }
            printf("fail to read_frame\n");
            break;
        }
        //avcodec_send_packet/avcodec_receive_frame
        //解码获取初始音频
        ret = avcodec_send_packet(decodec_ctx, input_packet);
        if (ret == AVERROR(EAGAIN)) {
            pkt_pending = true;
            continue;
        }
        if (ret < 0) {
            printf("Error sending a packet for decoding\n");
            break;
        }
        pkt_pending = false;
        while (ret >= 0) {
            ret = avcodec_receive_frame(decodec_ctx, pframeSRC);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            } else if (ret < 0) {
                printf("Error during decoding\n");
                break;
            }
            int source_samples = pframeSRC->nb_samples;
            int out_samples = source_samples;
            // uint8_t *write_2_pcm = NULL;
            if (out_samples != pframePCM->nb_samples){
                no_resample = 1;
                //读取到一帧音频或者视频
                //MP3->PCM,ret=swr_convert(pcm_convert_ctx, pframePCM->data, pframePCM->nb_samples,(const uint8_t **)pframeSRC->extended_data, pframeSRC->nb_samples);
                if (ret < 0) {
                    printf("[1]source_samples:%d, pframeSRC->nb_samples:%d,ret:%d\n", source_samples, pframeSRC->nb_samples, ret);
                    continue;
                } else {
                    //printf("[2]out_samples:%d, pframeSRC->nb_samples:%d,ret:%d\n", source_samples, pframeSRC->nb_samples, ret);
                }
                write_2_pcm = pframePCM->data[0];
                nb_data = ret;
            } else {
                printf("out_samples:%d, pframeSRC->nb_samples:%d  \n", out_samples, pframeSRC->nb_samples );
                nb_data = out_samples;
                write_2_pcm = pframeSRC->data[0];
            }
            //向硬件写入音频数据
            rc = snd_pcm_writei(handle, write_2_pcm, out_samples);
            if (rc == -EPIPE) {
                printf("underrun occurred\n");
                err=snd_pcm_prepare(handle);
                if(err < 0) {
                    printf("Can't recovery from underrun, prepare failed: %s\n", snd_strerror(err));
                    break;
                }
            }
            if (rc < 0) {
                printf("write to audio interface failed (%s)\n", snd_strerror(rc));
                break;
            }
            if (rc != out_samples) {
                printf("short write, write %d frames\n", rc);
            }
            av_packet_unref(input_packet);
        }
    }
    if (pcm_convert_ctx) {
        swr_free(&pcm_convert_ctx);
    }
    av_packet_free(&input_packet);
    if (pframeSRC) {
       av_frame_free(&pframeSRC);
    }
#if 1
    if (pframePCM) {
       av_frame_free(&pframePCM);
    }
#endif
    if(decodec_ctx != NULL){
        avcodec_close(decodec_ctx);
        avcodec_free_context(&decodec_ctx);
    }
    if (infmt_ctx != NULL) {
        avformat_close_input(&infmt_ctx);
        avformat_free_context(infmt_ctx);
    }
    snd_pcm_drain(handle);
    snd_pcm_close(handle);
    //free(converted_input_samples);
    free(buffer);
    free(alsa_device_name);
    return 0;
}
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参考:https://www.php.cn/link/94a5313663ab243911f0da89ed1096db

下一步计划是实现对rtsp流的请求。

2022/11/28更新:实现rtsp播放器,只需将播放路径直接设置为rtsp地址,操作非常简单!

Linux下使用ffmpeg播放mp3/aac/wav文件的音乐播放器应用

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