[FFmpeg-devel] [PATCH] Extracting NTP timestamp from RTCP

[Michael Niedermayer]

On Thu, Nov 07, 2013 at 02:47:40PM -0700, Fred Rothganger wrote:
> On 11/07/2013 01:55 PM, Michael Niedermayer wrote:
> >+                if (s->start_time_realtime == 0) {
> >+                    s->start_time_realtime =
> >+                          (((uint64_t) rtpctx->first_rtcp_ntp_time >> 32       ) - NTP_OFFSET) * 1000000
> >+                        + ((           rtpctx->first_rtcp_ntp_time & 0xFFFFFFFF)               * 1000000 >> 32);
> >why doesnt this use av_rescale ?
> >
> >
> 
> Mainly because I didn't think of it. I would still choose this code
> because the math is more efficient. Since this code executes very
> rarely, I gather your concern is more about readability. Attached is
> another patch that uses av_rescale.

>  doc/APIchanges         |    3 +++
>  libavformat/avformat.h |    2 +-
>  libavformat/rtsp.c     |   11 +++++++++++
>  libavformat/version.h  |    2 +-
>  4 files changed, 16 insertions(+), 2 deletions(-)
> 7531702dc18dcfdd6e3017380c977acba2cd5c54  rtsp.patch
> diff --git a/doc/APIchanges b/doc/APIchanges
> index dfdc159..be3d90a 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -15,6 +15,9 @@ libavutil:     2012-10-22
>  
>  API changes, most recent first:
>  
> +2013-11-07 - xxxxxxx - lavf 55.21.101 - avformat.h
> +  Set AVFormatContext.start_time_realtime when decoding.
> +
>  2013-11-xx - xxxxxxx - lavc 55.41.100 / 55.25.0 - avcodec.h
>                         lavu 52.51.100 - frame.h
>    Add ITU-R BT.2020 and other not yet included values to color primaries,
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index 6bd54ce..1c4929d 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -1127,7 +1127,7 @@ typedef struct AVFormatContext {
>       * since the unix epoch (00:00 1st January 1970). That is, pts=0
>       * in the stream was captured at this real world time.
>       * - encoding: Set by user.
> -     * - decoding: Unused.
> +     * - decoding: Set by libavformt.
>       */
>      int64_t start_time_realtime;
>  
> diff --git a/libavformat/rtsp.c b/libavformat/rtsp.c
> index 3b88fc7..e5fe53d 100644
> --- a/libavformat/rtsp.c
> +++ b/libavformat/rtsp.c
> @@ -2051,6 +2051,17 @@ redo:
>                   * as this one. */
>                  int i;
>                  AVStream *st = NULL;
> +                if (s->start_time_realtime == 0) {
> +                    s->start_time_realtime =
> +                          (((uint64_t) rtpctx->first_rtcp_ntp_time >> 32       ) - NTP_OFFSET) * 1000000
> +                        + av_rescale  (rtpctx->first_rtcp_ntp_time & 0xFFFFFFFF,                 1000000, 1LL << 32);

why is first_rtcp_ntp_time split in low and high 32bit halfs ?

[...]


-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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