FFmpeg解码音频和视频知识及代码演示

太过爱你忘了你带给我的痛 2023-10-13 11:19 11阅读 0赞

FFmpeg是一个开源的跨平台多媒体解决方案。它可以在命令行中执行各种音频和视频操作，如解码、编码、转换、裁剪、缩放等。

其中，解码音频和视频是FFmpeg的基本功能之一。本文将介绍FFmpeg解码音频和视频的知识和代码演示。

解码音频  
要解码音频，需要打开音频文件，获取音频流并解码。以下是解码音频的代码示例：

\`\`\`

include <stdio.h>  
include <stdlib.h>  
include <string.h>  
include <stdint.h>  
include <libavcodec/avcodec.h>  
include <libavformat/avformat.h>  
include <libavutil/audio\_fifo.h>  
include <libavutil/frame.h>  
int main(int argc, char\*\* argv) \{ // 打开输入音频文件 AVFormatContext\* formatctx = NULL; if (avformatopeninput(&formatctx, "input.mp3", NULL, NULL) != 0) \{ fprintf(stderr, "Failed to open input file\\n"); return -1; \}

// 获取音频流信息
    if (avformat_find_stream_info(format_ctx, NULL) < 0) {
        fprintf(stderr, "Failed to find stream information\n");
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 查找第一个音频流
    int audio_stream_idx = -1;
    for (int i = 0; i < format_ctx->nb_streams; i++) {
        if (format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            audio_stream_idx = i;
            break;
        }
    }
    if (audio_stream_idx == -1) {
        fprintf(stderr, "No audio stream found\n");
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 获取音频解码器
    AVCodec* codec = avcodec_find_decoder(format_ctx->streams[audio_stream_idx]->codecpar->codec_id);
    if (codec == NULL) {
        fprintf(stderr, "Unsupported codec\n");
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 打开音频解码器
    AVCodecContext* codec_ctx = avcodec_alloc_context3(codec);
    if (avcodec_parameters_to_context(codec_ctx, format_ctx->streams[audio_stream_idx]->codecpar) < 0) {
        fprintf(stderr, "Failed to copy codec parameters to decoder context\n");
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
    if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
        fprintf(stderr, "Failed to open codec\n");
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 初始化音频缓冲区和FIFO
    int frame_size = codec_ctx->frame_size;
    AVAudioFifo* fifo = av_audio_fifo_alloc(codec_ctx->sample_fmt, codec_ctx->channels, frame_size);
    if (fifo == NULL) {
        fprintf(stderr, "Failed to allocate audio FIFO\n");
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
    uint8_t** buffer = NULL;
    if (av_samples_alloc_array_and_samples(&buffer, NULL, codec_ctx->channels, frame_size, codec_ctx->sample_fmt, 0) < 0) {
        fprintf(stderr, "Failed to allocate audio buffer\n");
        av_audio_fifo_free(fifo);
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 解码音频流
    AVPacket packet;
    av_init_packet(&packet);
    while (av_read_frame(format_ctx, &packet) == 0) {
        if (packet.stream_index == audio_stream_idx) {
            int ret = avcodec_send_packet(codec_ctx, &packet);
            if (ret < 0) {
                fprintf(stderr, "Error sending a packet for decoding\n");
                break;
            }
            while (ret >= 0) {
                AVFrame* frame = av_frame_alloc();
                ret = avcodec_receive_frame(codec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    av_frame_free(&frame);
                    break;
                } else if (ret < 0) {
                    fprintf(stderr, "Error during decoding\n");
                    av_frame_free(&frame);
                    break;
                }
                int samples = av_samples_get_buffer_size(NULL, codec_ctx->channels, frame->nb_samples, codec_ctx->sample_fmt, 0);
                if (samples <= 0) {
                    av_frame_free(&frame);
                    continue;
                }
                memcpy(buffer[0], frame->data[0], samples);
                if (codec_ctx->channels > 1) {
                    memcpy(buffer[1], frame->data[1], samples / 2);
                }
                av_audio_fifo_write(fifo, (void**)buffer, frame->nb_samples);
                av_frame_free(&frame);
            }
        }
        av_packet_unref(&packet);
    }
    av_packet_unref(&packet);
     
    // 关闭音频解码器和输入文件，释放缓冲区和FIFO
    avcodec_free_context(&codec_ctx);
    avformat_close_input(&format_ctx);
    av_freep(&buffer[0]);
    av_freep(&buffer);
    av_audio_fifo_free(fifo);
     
    return 0;

解码视频  
要解码视频，需要打开视频文件，获取视频流并解码。以下是解码视频的代码示例：

\`\`\`

include <stdio.h>  
include <stdlib.h>  
include <string.h>  
include <stdint.h>  
include <libavcodec/avcodec.h>  
include <libavformat/avformat.h>  
include <libswscale/swscale.h>  
int main(int argc, char\*\* argv) \{ // 打开输入视频文件 AVFormatContext\* formatctx = NULL; if (avformatopeninput(&formatctx, "input.mp4", NULL, NULL) != 0) \{ fprintf(stderr, "Failed to open input file\\n"); return -1; \}

// 获取视频流信息
    if (avformat_find_stream_info(format_ctx, NULL) < 0) {
        fprintf(stderr, "Failed to find stream information\n");
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 查找第一个视频流
    int video_stream_idx = -1;
    for (int i = 0; i < format_ctx->nb_streams; i++) {
        if (format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_idx = i;
            break;
        }
    }
    if (video_stream_idx == -1) {
        fprintf(stderr, "No video stream found\n");
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 获取视频解码器
    AVCodec* codec = avcodec_find_decoder(format_ctx->streams[video_stream_idx]->codecpar->codec_id);
    if (codec == NULL) {
        fprintf(stderr, "Unsupported codec\n");
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 打开视频解码器
    AVCodecContext* codec_ctx = avcodec_alloc_context3(codec);
    if (avcodec_parameters_to_context(codec_ctx, format_ctx->streams[video_stream_idx]->codecpar) < 0) {
        fprintf(stderr, "Failed to copy codec parameters to decoder context\n");
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
    if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
        fprintf(stderr, "Failed to open codec\n");
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 初始化视频缓冲区和转换器
    AVFrame* frame = av_frame_alloc();
    AVFrame* rgb_frame = av_frame_alloc();
    uint8_t* buffer = NULL;
    int num_bytes = av_image_get_buffer_size(AV_PIX_FMT_RGB24, codec_ctx->width, codec_ctx->height, 1);
    if (num_bytes <= 0) {
        fprintf(stderr, "Failed to get image buffer size\n");
        av_frame_free(&rgb_frame);
        av_frame_free(&frame);
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
    buffer = (uint8_t*)av_malloc(num_bytes * sizeof(uint8_t));
    if (buffer == NULL) {
        fprintf(stderr, "Failed to allocate image buffer\n");
        av_frame_free(&rgb_frame);
        av_frame_free(&frame);
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
    av_image_fill_arrays(rgb_frame->data, rgb_frame->linesize, buffer, AV_PIX_FMT_RGB24, codec_ctx->width, codec_ctx->height, 1);
    struct SwsContext* sws_ctx = sws_getContext(codec_ctx->width, codec_ctx->height, codec_ctx->pix_fmt, codec_ctx->width, codec_ctx->height, AV_PIX_FMT_RGB24, SWS_BILINEAR, NULL, NULL, NULL);
    if (sws_ctx == NULL) {
        fprintf(stderr, "Failed to initialize color conversion context\n");
        av_freep(&buffer);
        av_frame_free(&rgb_frame);
        av_frame_free(&frame);
        avcodec_free_context(&codec_ctx);
        avformat_close_input(&format_ctx);
        return -1;
    }
     
    // 解码视频流
    AVPacket packet;
    av_init_packet(&packet);
    while (av_read_frame(format_ctx, &packet) == 0) {
        if (packet.stream_index == video_stream_idx) {
            int ret = avcodec_send_packet(codec_ctx, &packet);
            if (ret < 0) {
                fprintf(stderr, "Error sending a packet for decoding\n");
                break;
            }
            while (ret >= 0) {
                ret = avcodec_receive_frame(codec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    fprintf(stderr, "Error during decoding\n");
                    break;
                }
                sws_scale(sws_ctx, frame->data, frame->linesize, 0, codec_ctx->height, rgb_frame->data, rgb_frame->linesize);
                // 在此处可以将RGB图像显示或保存到文件中
            }
        }
        av_packet_unref(&packet);
    }
    av_packet_unref(&packet);
     
    // 关闭视频解码器和输入文件，释放缓冲区和转换器
    sws_freeContext(sws_ctx);
    av_freep(&buffer);
    av_frame_free(&rgb_frame);
    av_frame_free(&frame);
    avcodec_free_context(&codec_ctx);
    avformat_close_input(&format_ctx);
     
    return 0;

\} \`\`\`

上述代码示例展示了如何使用FFmpeg解码音频和视频。在实际应用中，还需要根据具体的需求对解码后的音频和视频进行处理、保存或播放等操作。