We fetch a camera stream over RTSP (Axis Q1755 H264). And after a random time we a start recording the stream to a file. I check the video file with ffprobe and realise the start time is not the start time of the recording it is the start time of fetch the stream. My Video has a length of 5 seconds and the start time of the video should be 0. But the real starttime of the Video is at second 20. This leads to a an incorrect timebase. (ffmpeg Version 3.3.3)
I try to repair it, but now i have some time the error timebase 1/180000... i marked my changes with the comment (timebase repair logic)
ffprobe Output (without timebase repair logic)
The start is higher as the duration, correctly the start is 0 and not 20.080000
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
'C:\testvideo.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.71.100 Duration: 00:00:05.04, start: 20.080000, bitrate: 2675 kb/s
Stream #0:0(und): Video: h264 (Baseline) (avc1 / 0x31637661), yuvj420p(pc, bt709), 800x450 [SAR 1:1 DAR 16:9], 2670 kb/s, 50.20 fps,
50 tbr, 180k tbn, 360k tbc (default)
Metadata:
handler_name : VideoHandler
Error after the add of timebase repair logic
[mpeg4 @ 00000178fcb12b40] timebase 1/180000 not supported by MPEG 4 standard, the maximum admitted value for the timebase denominator is 65535 Could not open codec 'mpeg4': Unspecified error Cannot start recording
Here some parts of my code
Start Logic
bool RecordingStreamGrabber::start()
{
CORE_LOG_INFO(m_logger, "Started RecordingStreamGrabber");
if (m_thread == NULL)
{
if (this->prepareInputStream())
{
m_run = true;
m_thread = new std::thread(RecordingStreamGrabber::run, this);
return true;
}
CORE_LOG_ERROR(m_logger, "Error starting RecrodingStreamGrabber");
return false;
}
return false;
}
Prepare Input/Output Stream
bool RecordingStreamGrabber::prepareInputStream()
{
CORE_LOG_INFO(m_logger, "Preparing Inputstream for recording: " << m_url);
m_ifmtctx = avformat_alloc_context();
interrupt_recording_nostop = false;
interrupt_recording_timeout = m_timeout; // Timeout in milisekunde
interrupt_recording_starttime = GetTickCount();
m_ifmtctx->interrupt_callback = interrupt_timeout_cb;
if (avformat_open_input(&m_ifmtctx, m_url.c_str(), NULL, NULL) != 0)
{
m_ifmtctx = NULL;
CORE_LOG_ERROR(m_logger, "Error opening recording URL: " << m_url);
return false;
}
interrupt_recording_nostop = true;
if (avformat_find_stream_info(m_ifmtctx, NULL) < 0)
{
CORE_LOG_ERROR(m_logger, "Error finding stream in URL: " << m_url);
avformat_close_input(&m_ifmtctx);
m_ifmtctx = NULL;
return false;
}
//search for the first video stream
m_stream_index = -1;
for (unsigned int i = 0; i < m_ifmtctx->nb_streams && m_stream_index == -1; i++)
{
m_iccx = m_ifmtctx->streams[i]->codec;
if (m_iccx->codec_type == AVMEDIA_TYPE_VIDEO)
{
m_istream = m_ifmtctx->streams[i];
m_stream_index = i;
}
}
if (m_stream_index == -1)
{
CORE_LOG_ERROR(m_logger, "Could not find video stream in URL: " << m_url);
avformat_close_input(&m_ifmtctx);
m_ifmtctx = NULL;
return false;
}
return true;
}
bool RecordingStreamGrabber::prepareOutputStream()
{
if (m_ofmtctx)
{
CORE_LOG_DEBUG(m_logger, "Close outputfile: " << m_targetfile);
avformat_free_context(m_ofmtctx);
m_ofmtctx = NULL;
}
m_ofmt = av_guess_format(NULL, m_targetfile.c_str(), NULL);
m_ofmtctx = avformat_alloc_context();
m_ofmtctx->oformat = m_ofmt;
if (avio_open2(&m_ofmtctx->pb, m_targetfile.c_str(), AVIO_FLAG_WRITE, NULL, NULL) != 0)
{
avformat_free_context(m_ofmtctx);
m_ofmtctx = NULL;
CORE_LOG_ERROR(m_logger, "Error opening outputfile: " << m_targetfile);
return false;
}
m_ostream = avformat_new_stream(m_ofmtctx, NULL);
avcodec_copy_context(m_ostream->codec, m_iccx);
m_ostream->sample_aspect_ratio.num = m_iccx->sample_aspect_ratio.num;
m_ostream->sample_aspect_ratio.den = m_iccx->sample_aspect_ratio.den;
/* time base: this is the fundamental unit of time (in seconds) in terms
of which frame timestamps are represented. for fixed-fps content,
timebase should be 1/framerate and timestamp increments should be
identically 1. */
m_ostream->time_base.num = m_iccx->time_base.num;
m_ostream->time_base.den = m_iccx->time_base.den;
avformat_write_header(m_ofmtctx, NULL);
#ifdef WIN32
sprintf_s(m_ofmtctx->filename, sizeof(m_ofmtctx->filename), "%s", m_targetfile.c_str());
#else
snprintf(m_ofmtctx->filename, sizeof(m_ofmtctx->filename), "%s", m_targetfile.c_str());
#endif
return true;
}
Recording Logic
void RecordingStreamGrabber::run(RecordingStreamGrabber *_this)
{
AVPacket packet;
av_init_packet(&packet);
int i = 0;
bool startFrame = true;
bool keyFrame = false;
int64_t pts, dts;
_this->m_tailWritten = true;
while (_this->m_run)
{
if (av_read_frame(_this->m_ifmtctx, &packet) >= 0)
{
if ((packet.flags & AV_PKT_FLAG_KEY) == AV_PKT_FLAG_KEY)
{
keyFrame = true;
CORE_LOG_DEBUG(_this->m_logger, "Detected key frame: " << i << "");
}
if (_this->m_record)
{
if (packet.stream_index == _this->m_stream_index)
{
packet.stream_index = _this->m_ostream->id;
if (_this->m_tailWritten == false || keyFrame == true)
{
//#####################################
//timebase repair logic (my changes)
//#####################################
AVStream *in_stream;
AVStream *out_stream;
in_stream = _this->m_ifmtctx->streams[packet.stream_index];
out_stream = _this->m_ofmtctx->streams[packet.stream_index];
if (startFrame)
{
pts = packet.pts;
dts = packet.dts;
startFrame = false;
}
packet.pts -= pts;
packet.dts -= dts;
packet.pts = av_rescale_q_rnd(packet.pts, in_stream->time_base, out_stream->time_base, (AVRounding)((int)AV_ROUND_NEAR_INF | (int)AV_ROUND_PASS_MINMAX));
packet.dts = av_rescale_q_rnd(packet.dts, in_stream->time_base, out_stream->time_base, (AVRounding)((int)AV_ROUND_NEAR_INF | (int)AV_ROUND_PASS_MINMAX));
packet.duration = av_rescale_q(packet.duration, in_stream->time_base, out_stream->time_base);
//end of my changes
av_interleaved_write_frame(_this->m_ofmtctx, &packet);
_this->m_tailWritten = false;
}
}
}
else if (_this->m_ofmtctx)
{
if (_this->m_tailWritten == false)
{
av_write_trailer(_this->m_ofmtctx);
avio_close(_this->m_ofmtctx->pb);
}
avformat_free_context(_this->m_ofmtctx);
_this->m_tailWritten = true;
_this->m_ofmtctx = NULL;
startFrame = true;
}
i++;
keyFrame = false;
}
av_free_packet(&packet);
av_init_packet(&packet);
}
if (_this->m_record)
{
av_write_trailer(_this->m_ofmtctx);
avio_close(_this->m_ofmtctx->pb);
}
if (_this->m_ofmtctx)
{
avformat_free_context(_this->m_ofmtctx);
_this->m_ofmtctx = NULL;
}
_this->m_record = false;
avformat_close_input(&_this->m_ifmtctx);
_this->m_ifmtctx = NULL;
}
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