[FFmpeg-devel] [PATCH] avformat/rtpdec: attach producer reference time if available

[James Almer]

On 3/17/2021 9:28 PM, Alok Priyadarshi wrote:
> This produces true wallclock time at rtp source instead of the
> local wallclock time at rtp client.
> ---
>   libavformat/internal.h |  8 ++++++++
>   libavformat/rtpdec.c   | 10 ++++++++++
>   libavformat/utils.c    |  9 +++++++++
>   3 files changed, 27 insertions(+)
> 
> diff --git a/libavformat/internal.h b/libavformat/internal.h
> index 17a6ab07d3..1e10cde00e 100644
> --- a/libavformat/internal.h
> +++ b/libavformat/internal.h
> @@ -254,6 +254,14 @@ uint64_t ff_ntp_time(void);
>    */
>   uint64_t ff_get_formatted_ntp_time(uint64_t ntp_time_us);
>   
> +/**
> + * Parse the NTP time in micro seconds (since NTP epoch).
> + *
> + * @param ntp_ts NTP time stamp formatted as per the RFC-5905.
> + * @return the time in micro seconds (since NTP epoch)
> + */
> +uint64_t ff_parse_ntp_time(uint64_t ntp_ts);
> +
>   /**
>    * Append the media-specific SDP fragment for the media stream c
>    * to the buffer buff.
> diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> index 3d5b200099..3e5f280f2f 100644
> --- a/libavformat/rtpdec.c
> +++ b/libavformat/rtpdec.c
> @@ -23,6 +23,7 @@
>   #include "libavutil/avstring.h"
>   #include "libavutil/intreadwrite.h"
>   #include "libavutil/time.h"
> +#include "libavcodec/packet_internal.h"
>   
>   #include "avformat.h"
>   #include "network.h"
> @@ -30,6 +31,7 @@
>   #include "url.h"
>   #include "rtpdec.h"
>   #include "rtpdec_formats.h"
> +#include "internal.h"
>   
>   #define MIN_FEEDBACK_INTERVAL 200000 /* 200 ms in us */
>   
> @@ -594,6 +596,14 @@ static void finalize_packet(RTPDemuxContext *s, AVPacket *pkt, uint32_t timestam
>       if (timestamp == RTP_NOTS_VALUE)
>           return;
>   
> +    if (s->last_rtcp_ntp_time != AV_NOPTS_VALUE) {
> +        uint64_t prft_us = ff_parse_ntp_time(s->last_rtcp_ntp_time) - NTP_OFFSET_US +
> +                           timestamp - s->last_rtcp_timestamp;
> +        if (ff_side_data_set_prft(pkt, prft_us) < 0) {

This is a libavcodec function. It can't be used from libavformat. You 
should instead manually add the side data using 
av_packet_new_side_data(pkt, AV_PKT_DATA_PRFT, 
sizeof(AVProducerReferenceTime)), then filling both the struct's 
wallclock and flags fields following the definition in the struct's doxy 
and ISO/IEC 14496-12, so flags should probably be 24.

That being said, what is expected to use this value? Decoders don't care 
about prft, so is your usecase a remuxing one?

> +            av_log(s->ic, AV_LOG_WARNING, "rtpdec: failed to set prft");
> +        }
> +    }
> +
>       if (s->last_rtcp_ntp_time != AV_NOPTS_VALUE && s->ic->nb_streams > 1) {
>           int64_t addend;
>           int delta_timestamp;
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index 7e5767ec60..569922beaf 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -4734,6 +4734,15 @@ uint64_t ff_get_formatted_ntp_time(uint64_t ntp_time_us)
>       return ntp_ts;
>   }
>   
> +uint64_t ff_parse_ntp_time(uint64_t ntp_ts)
> +{
> +    uint64_t sec = ntp_ts >> 32;
> +    uint64_t frac_part = ntp_ts & 0xFFFFFFFFULL;
> +    uint64_t usec = (frac_part * 1000000) / 0xFFFFFFFFULL;
> +
> +    return (sec * 1000000) + usec;
> +}
> +
>   int av_get_frame_filename2(char *buf, int buf_size, const char *path, int number, int flags)
>   {
>       const char *p;
>