[FFmpeg-devel] [PATCH 1/3] avformat/utils: function to get the formatted ntp time

[Michael Niedermayer]

On Tue, Apr 24, 2018 at 02:46:56PM +0530, vdixit at akamai.com wrote:
> From: Vishwanath Dixit <vdixit at akamai.com>
> 
> This utility function creates 64-bit NTP time format as per the RFC
> 5905.
> A simple explaination of 64-bit NTP time format is here
> http://www.beaglesoft.com/Manual/page53.htm
> ---
>  libavformat/internal.h |  8 ++++++++
>  libavformat/utils.c    | 20 ++++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/libavformat/internal.h b/libavformat/internal.h
> index 3582682..e9f758f 100644
> --- a/libavformat/internal.h
> +++ b/libavformat/internal.h
> @@ -240,6 +240,14 @@ void ff_read_frame_flush(AVFormatContext *s);
>  uint64_t ff_ntp_time(void);
>  
>  /**
> + * Get the NTP time stamp formatted as per the RFC-5905.
> + *
> + * @param ntp_time NTP time in micro seconds (since NTP epoch)
> + * @return the formatted NTP time stamp
> + */
> +uint64_t ff_time_ntp_format(uint64_t ntp_time);
> +
> +/**
>   * Append the media-specific SDP fragment for the media stream c
>   * to the buffer buff.
>   *
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index c25eab4..b59d426 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -4637,6 +4637,26 @@ uint64_t ff_ntp_time(void)
>      return (av_gettime() / 1000) * 1000 + NTP_OFFSET_US;
>  }
>  
> +uint64_t ff_time_ntp_format(uint64_t ntp_time)
> +{
> +    uint64_t ntp_ts, frac_part;
> +    uint32_t sec, usec;
> +
> +    //current ntp time in seconds and micro seconds

> +    sec = ntp_time / 1000000;

This can be truncated


> +    usec = ntp_time % 1000000;
> +
> +    //encoding in ntp timestamp format
> +    frac_part = usec * 0xFFFFFFFFULL;
> +    frac_part /= 1000000;
> +
> +    ntp_ts = (uint64_t) sec;
> +    ntp_ts <<= 32;
> +    ntp_ts |= frac_part;
> +
> +    return ntp_ts;

this looks similar to what av_rescale does.


also ff_time_ntp_format() is a bad name. It does not give any hint
on if ntp time is the input or output of the call

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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