if ((ret = rtspCtx->ctx->iformat->read_header(rtspCtx->ctx, &ap)) < 0){ av_log(NULL, AV_LOG_ERROR, "[%s:%d\n]read_header failed ret=%d,filename=%s", __FUNCTION__, __LINE__,ret,rtspCtx->ctx->filename); goto fail; }

这段代码是用于读取 RTSP 流的头信息，其中 rtspCtx 是一个 RTSP 上下文结构体，ctx 是一个 AVFormatContext 结构体，iformat 指向了 AVInputFormat 结构体，read_header 是 AVInputFormat 结构体中的函数指针，用于读取媒体文件的头信息。如果读取失败，会输出错误信息并跳转到 fail 标签处进行错误处理。

相关问题

基于ffmpeg-3.3.4的只播放MP4文件的音频demo

以下是基于 FFmpeg 3.3.4 的只播放 MP4 文件音频的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/frame.h>
#include <libavutil/mem.h>
#include <libavutil/time.h>
#include <libavutil/opt.h>

#define AUDIO_INBUF_SIZE 20480
#define AUDIO_REFILL_THRESH 4096

static int quit = 0;

static void sigterm_handler(int sig)
{
    quit = 1;
}

int main(int argc, char **argv)
{
    AVFormatContext *fmt_ctx = NULL;
    AVCodecContext *dec_ctx = NULL;
    AVCodec *dec = NULL;
    int stream_idx = -1;
    AVPacket pkt;
    AVFrame *frame = NULL;
    uint8_t inbuf[AUDIO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
    int inbuf_size;
    AVPacket avpkt;
    int ret;
    int64_t pts;
    int64_t duration;

    if (argc <= 1) {
        fprintf(stderr, "Usage: %s <input file>\n", argv[0]);
        exit(0);
    }

    signal(SIGINT, sigterm_handler);
    signal(SIGTERM, sigterm_handler);

    av_register_all();

    if (avformat_open_input(&fmt_ctx, argv[1], NULL, NULL) < 0) {
        fprintf(stderr, "Could not open input file '%s'", argv[1]);
        exit(1);
    }

    if (avformat_find_stream_info(fmt_ctx, NULL) < 0) {
        fprintf(stderr, "Could not find stream information");
        exit(1);
    }

    av_dump_format(fmt_ctx, 0, argv[1], 0);

    for (int i = 0; i < fmt_ctx->nb_streams; i++) {
        if (fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            stream_idx = i;
            break;
        }
    }

    if (stream_idx == -1) {
        fprintf(stderr, "Could not find audio stream");
        exit(1);
    }

    dec = avcodec_find_decoder(fmt_ctx->streams[stream_idx]->codecpar->codec_id);
    if (!dec) {
        fprintf(stderr, "Failed to find codec\n");
        exit(1);
    }

    dec_ctx = avcodec_alloc_context3(dec);
    if (!dec_ctx) {
        fprintf(stderr, "Failed to allocate codec context\n");
        exit(1);
    }

    if (avcodec_parameters_to_context(dec_ctx, fmt_ctx->streams[stream_idx]->codecpar) < 0) {
        fprintf(stderr, "Failed to copy codec parameters to codec context\n");
        exit(1);
    }

    if (avcodec_open2(dec_ctx, dec, NULL) < 0) {
        fprintf(stderr, "Failed to open codec\n");
        exit(1);
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Failed to allocate frame\n");
        exit(1);
    }

    pts = AV_NOPTS_VALUE;
    duration = AV_NOPTS_VALUE;

    while (av_read_frame(fmt_ctx, &pkt) >= 0) {
        if (pkt.stream_index == stream_idx) {
            avpkt = pkt;
            while (avpkt.size > 0) {
                ret = avcodec_send_packet(dec_ctx, &avpkt);
                if (ret < 0) {
                    fprintf(stderr, "Error sending a packet for decoding\n");
                    break;
                }

                while (ret >= 0) {
                    ret = avcodec_receive_frame(dec_ctx, frame);
                    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                        break;
                    } else if (ret < 0) {
                        fprintf(stderr, "Error during decoding\n");
                        exit(1);
                    }

                    if (pts == AV_NOPTS_VALUE) {
                        pts = frame->pts;
                    }

                    if (duration == AV_NOPTS_VALUE) {
                        duration = frame->pkt_duration;
                    }

                    inbuf_size = av_samples_get_buffer_size(NULL, dec_ctx->channels, frame->nb_samples,
                                                            dec_ctx->sample_fmt, 1);
                    memcpy(inbuf, frame->data[0], inbuf_size);

                    // Play audio
                    write(STDOUT_FILENO, inbuf, inbuf_size);
                }

                avpkt.size -= ret;
                avpkt.data += ret;
            }
        }

        av_packet_unref(&pkt);

        if (quit) {
            break;
        }
    }

    avcodec_free_context(&dec_ctx);
    avformat_close_input(&fmt_ctx);
    av_frame_free(&frame);
    av_free(inbuf);

    return 0;
}

这个示例代码会读取 MP4 文件中的音频数据，并将其输出到标准输出。您可以将标准输出重定向到音频播放程序中，以实现播放音频的功能。

请注意，在实际使用中，需要根据具体的需求添加错误处理、参数配置等功能。

ffmpeg_g -re -i /home/tsdl/Downloads/FPV_2021-0-1_12-37-23.h264 -vcodec libx264 -profile:v baseline -r 25 -g 50 -f rtc "http://192.168.114.34:1985/rtc/v1/whip/?app=live&stream=livestream"将上面命令使用FFmpeg最新的API转化成C语言代码

以下是将给定的FFmpeg命令使用最新的API转换为C语言代码的示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>

int main(int argc, char *argv[]) {
    AVFormatContext *fmt_ctx = NULL;
    AVCodecContext *video_dec_ctx = NULL, *video_enc_ctx = NULL;
    AVCodec *video_dec = NULL, *video_enc = NULL;
    AVStream *video_stream = NULL;
    AVOutputFormat *output_fmt = NULL;
    AVFormatContext *output_fmt_ctx = NULL;
    AVPacket pkt;
    int ret, i;

    // Initialize the AVFormatContext
    if ((ret = avformat_open_input(&fmt_ctx, "/home/tsdl/Downloads/FPV_2021-0-1_12-37-23.h264", NULL, NULL)) < 0) {
        fprintf(stderr, "Could not open input file\n");
        exit(1);
    }

    if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        exit(1);
    }

    // Find the video stream
    for (i = 0; i < fmt_ctx->nb_streams; i++) {
        if (fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream = fmt_ctx->streams[i];
            break;
        }
    }

    if (!video_stream) {
        fprintf(stderr, "Could not find video stream\n");
        exit(1);
    }

    // Initialize the video decoder
    video_dec = avcodec_find_decoder(video_stream->codecpar->codec_id);
    if (!video_dec) {
        fprintf(stderr, "Could not find video decoder\n");
        exit(1);
    }

    video_dec_ctx = avcodec_alloc_context3(video_dec);
    if (!video_dec_ctx) {
        fprintf(stderr, "Could not allocate video decoder context\n");
        exit(1);
    }

    if ((ret = avcodec_parameters_to_context(video_dec_ctx, video_stream->codecpar)) < 0) {
        fprintf(stderr, "Could not initialize video decoder context\n");
        exit(1);
    }

    if ((ret = avcodec_open2(video_dec_ctx, video_dec, NULL)) < 0) {
        fprintf(stderr, "Could not open video decoder\n");
        exit(1);
    }

    // Initialize the video encoder
    video_enc = avcodec_find_encoder_by_name("libx264");
    if (!video_enc) {
        fprintf(stderr, "Could not find video encoder\n");
        exit(1);
    }

    video_enc_ctx = avcodec_alloc_context3(video_enc);
    if (!video_enc_ctx) {
        fprintf(stderr, "Could not allocate video encoder context\n");
        exit(1);
    }

    // Set video encoder options
    av_opt_set(video_enc_ctx->priv_data, "profile", "baseline", 0);
    av_opt_set(video_enc_ctx->priv_data, "tune", "zerolatency", 0);
    video_enc_ctx->width = video_dec_ctx->width;
    video_enc_ctx->height = video_dec_ctx->height;
    video_enc_ctx->sample_aspect_ratio = video_dec_ctx->sample_aspect_ratio;
    video_enc_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    video_enc_ctx->time_base = av_inv_q(video_stream->avg_frame_rate);
    video_enc_ctx->gop_size = 50;
    video_enc_ctx->framerate = video_stream->avg_frame_rate;

    if ((ret = avcodec_open2(video_enc_ctx, video_enc, NULL)) < 0) {
        fprintf(stderr, "Could not open video encoder\n");
        exit(1);
    }

    // Initialize the output format context
    if ((ret = avformat_alloc_output_context2(&output_fmt_ctx, NULL, "rtc", "http://192.168.114.34:1985/rtc/v1/whip/?app=live&stream=livestream")) < 0) {
        fprintf(stderr, "Could not allocate output format context\n");
        exit(1);
    }

    output_fmt = output_fmt_ctx->oformat;

    // Add the video stream to the output format context
    video_stream = avformat_new_stream(output_fmt_ctx, NULL);
    if (!video_stream) {
        fprintf(stderr, "Could not create video stream\n");
        exit(1);
    }

    video_stream->codecpar->codec_id = video_enc->id;
    video_stream->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
    video_stream->codecpar->width = video_enc_ctx->width;
    video_stream->codecpar->height = video_enc_ctx->height;
    video_stream->codecpar->format = video_enc_ctx->pix_fmt;
    video_stream->codecpar->codec_tag = 0;
    avcodec_parameters_to_context(video_stream->codec, video_stream->codecpar);

    // Write the output format header
    if ((ret = avformat_write_header(output_fmt_ctx, NULL)) < 0) {
        fprintf(stderr, "Could not write output format header\n");
        exit(1);
    }

    // Read frames from input, encode and write to output
    while (1) {
        if ((ret = av_read_frame(fmt_ctx, &pkt)) < 0) {
            break;
        }

        if (pkt.stream_index == video_stream->index) {
            av_packet_rescale_ts(&pkt, video_stream->time_base, video_enc_ctx->time_base);
            pkt.flags |= AV_PKT_FLAG_KEY;

            if ((ret = avcodec_send_packet(video_enc_ctx, &pkt)) < 0) {
                fprintf(stderr, "Could not send packet to video encoder\n");
                exit(1);
            }

            while (ret >= 0) {
                ret = avcodec_receive_packet(video_enc_ctx, &pkt);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    fprintf(stderr, "Error encoding video frame\n");
                    exit(1);
                }

                av_packet_rescale_ts(&pkt, video_enc_ctx->time_base, video_stream->time_base);
                pkt.stream_index = video_stream->index;

                if ((ret = av_interleaved_write_frame(output_fmt_ctx, &pkt)) < 0) {
                    fprintf(stderr, "Error writing video frame\n");
                    exit(1);
                }

                av_packet_unref(&pkt);
            }
        }

        av_packet_unref(&pkt);
    }

    // Write the output format trailer
    av_write_trailer(output_fmt_ctx);

    // Cleanup
    avformat_close_input(&fmt_ctx);
    avcodec_free_context(&video_dec_ctx);
    avcodec_free_context(&video_enc_ctx);
    avformat_free_context(output_fmt_ctx);

    return 0;
}

注意：以上示例代码仅供参考，具体实现可能需要根据您的需求进行修改。同时，您需要添加FFmpeg库的链接，并将FFmpeg头文件和库文件添加到编译路径中。