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

[Dixit, Vishwanath]

On 4/26/18 1:04 AM, Michael Niedermayer wrote:
> 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
Yes, but the truncated part is not getting discarded, as the following line is taking care of that. Please correct me if I have not understood what you have intended to say here.
>
>
>> +    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.
Not really. This is a unique format as defined in RFC 5905. (please see this page for high level understanding of this format http://www.beaglesoft.com/Manual/page53.htm )
>
>
> 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
Okay. I will submit a revised patch with a more meaningful function name. How does 'ff_get_formatted_ntp_time' sound like?
>
> [...]
>
>
>
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