我很难弄清楚在哪里可以找到这个..
我正在构建一个简单的记录器来了解这个视频压缩宇宙，我面临着一些奇怪的行为..
在此之前，我需要解释一下场景......
它非常简单......每次我调用 av_read_frame( input_context, input_packet ) 我将 pts 保存到 last_pts 变量中......
所以...
困扰我的是，我对 av_read_frame 的调用中约有 10% 得到 input_packet.pts > last_pts
当我尝试这样做时，导致来自编码器的错误消息......考虑到这一点，我决定在它发生时丢弃这些帧......
我认为仅仅丢帧不是一个好主意，因为如果我得到它们，它就需要以某种方式......
那么......当 last_pts > current_pts 时该怎么办？
我将粘贴我的测试代码，我使用从网络摄像头捕获视频并使用 libx264 编码器保存到 mp4 文件
#include <QCoreApplication>
extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <libavutil/avutil.h>
#include <libavdevice/avdevice.h>
}
#include <QTime>
#include <QThread>
#include <QDebug>
#define SM_DEBUG
static const double max_fps = 30;
static const double min_loop_duration = 1000 / max_fps;
static const double max_duration = 5; // in seconds
static void sleep_if_needed(const int &elapsed) {
int sleep_duration = min_loop_duration - elapsed;
if (sleep_duration > 0) {
QThread::msleep(sleep_duration);
}
}
#ifdef SM_DEBUG
static void log_packet(const AVPacket *pkt,
const AVRational &time_base,
int is_input=0)
{
qDebug() << ((is_input) ? QString(">>") : QString("<<")) << "Size:" << QString::number(pkt->size) <<
"pts:" << QString::number(pkt->pts) <<
"pts_time:" << QString::number(av_q2d(time_base) * pkt->pts) <<
"dts:" << QString::number(pkt->dts) <<
"dts_time:" << QString::number(av_q2d(time_base) * pkt->dts);
}
#endif
int main()
{
int input_w, input_h, output_w = 640, output_h = 480;
av_register_all();
avdevice_register_all();
avcodec_register_all();
#ifdef SM_DEBUG
av_log_set_level(AV_LOG_DEBUG);
#else
av_log_set_level(AV_LOG_ERROR);
#endif
AVFormatContext *ic;
AVFormatContext *oc;
AVInputFormat *ifmt;
AVDictionary *opts = 0;
AVCodecContext* dec_ctx;
AVCodecContext* enc_ctx;
AVCodec *dec;
AVCodec *enc;
AVStream* ist;
AVStream* ost;
ifmt = av_find_input_format("v4l2");
av_dict_set(&opts, "tune", "zerolatency", AV_DICT_APPEND);
ic = avformat_alloc_context();
ic->flags |= AVFMT_FLAG_NONBLOCK;
avformat_open_input(&ic, "/dev/video0", ifmt, &opts);
avformat_find_stream_info(ic, NULL);
av_dump_format(ic, 0, ic->filename, 0);
AVFrame *frame;
AVFrame *tmp_frame;
ist = ic->streams[0];
dec_ctx = ist->codec;
input_w = dec_ctx->width;
input_h = dec_ctx->height;
dec_ctx->flags |= CODEC_FLAG_LOW_DELAY;
dec = avcodec_find_decoder(dec_ctx->codec_id);
av_format_set_video_codec(ic, dec);
avcodec_open2(dec_ctx, dec, NULL);
// output
avformat_alloc_output_context2(&oc, NULL, "MP4", "/home/poste9/grava.mp4");
enc = avcodec_find_encoder(AV_CODEC_ID_H264);
ost = avformat_new_stream(oc, enc);
enc_ctx = ost->codec;
enc_ctx->codec_id = AV_CODEC_ID_H264;
enc_ctx->width = output_w;
enc_ctx->height = output_h;
ost->time_base.num = ist->time_base.num;
ost->time_base.den = ist->time_base.den;
enc_ctx->time_base = ost->time_base;
enc_ctx->gop_size = 250;
enc_ctx->keyint_min = 25;
enc_ctx->qmax = 51;
enc_ctx->qmin = 30;
enc_ctx->pix_fmt = AV_PIX_FMT_YUV422P;
enc_ctx->max_b_frames = 6;
enc_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
enc_ctx->flags |= CODEC_FLAG_LOW_DELAY;
avcodec_open2(enc_ctx, enc, NULL);
avio_open2(&oc->pb, oc->filename, AVIO_FLAG_WRITE,
&oc->interrupt_callback, NULL);
av_dump_format(oc, 0, oc->filename, 1);
avformat_write_header(oc, NULL);
struct SwsContext *sws_ctx;
sws_ctx = sws_getContext(input_w, input_h,
dec_ctx->pix_fmt,
output_w, output_h, enc_ctx->pix_fmt,
SWS_BICUBIC, NULL, NULL, NULL);
frame = av_frame_alloc();
tmp_frame = av_frame_alloc();
frame->format = enc_ctx->pix_fmt;
frame->width = output_w;
frame->height = output_h;
frame->pts = AV_NOPTS_VALUE;
av_frame_get_buffer(frame, 32);
av_frame_make_writable(frame);
int got_picture=0;
int got_packet=0;
double recording_duration = 0;
QTime timer;
AVPacket pkt_out;
av_init_packet(&pkt_out);
timer.start();
bool started_recording = false;
int64_t start_time = 0;
int64_t last_pts = INT64_MIN;
while(1) {
timer.restart();
AVPacket pkt_in;
av_read_frame(ic, &pkt_in);
if (pkt_in.size == 0) {
sleep_if_needed(timer.elapsed());
continue;
}
avcodec_decode_video2(dec_ctx, tmp_frame, &got_picture, &pkt_in);
#ifdef SM_DEBUG
log_packet(&pkt_in, ist->time_base, 1);
#endif
if (!started_recording) {
start_time = pkt_in.dts;
started_recording = true;
}
if (pkt_in.pts < last_pts) {
sleep_if_needed(timer.elapsed());
continue;
}
last_pts = pkt_in.pts;
frame->pts = (pkt_in.dts - start_time);
if (!got_picture) {
av_free_packet(&pkt_in);
sleep_if_needed(timer.elapsed());
continue;
} else {
sws_scale(sws_ctx, tmp_frame->data, tmp_frame->linesize,
0, input_h, frame->data, frame->linesize);
av_free_packet(&pkt_in);
}
av_init_packet(&pkt_out);
avcodec_encode_video2(enc_ctx, &pkt_out, frame, &got_packet);
if (got_packet) {
if (pkt_out.pts < pkt_out.dts) {
pkt_out.dts = pkt_out.pts;
}
pkt_out.stream_index = 0;
recording_duration = pkt_out.pts * av_q2d(ost->time_base);
#ifdef SM_DEBUG
log_packet(&pkt_out, ost->time_base, 0);
#endif
av_interleaved_write_frame(oc, &pkt_out);
av_free_packet(&pkt_out);
}
if (recording_duration >= max_duration) {
break;
} else {
sleep_if_needed(timer.elapsed());
}
}
av_write_trailer(oc);
av_dict_free(&opts);
av_frame_free(&frame);
av_frame_free(&tmp_frame);
sws_freeContext(sws_ctx);
avcodec_close(dec_ctx);
avcodec_close(enc_ctx);
avio_close(oc->pb);
avformat_free_context(oc);
avformat_close_input(&ic);
return 0;
}