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This commit introduces the AVTP Clock Reference Format (CRF) Synchronizer element. This element implements the AVTP CRF Listener as described in IEEE 1722-2016 Section 10. CRF is useful in synchronizing events within different systems by distributing a common clock. This is useful in a scenario where there are multiple talkers who are sending data to a single listener which is processing that data. E.g. CCTV cameras on a network sending AVTP video streams to a base station to display on the same screen. It is assumed that all the systems are already time-synchronized with each other. So, the AVTP Talker essentially adjusts the AVTP Presentation Time so it's phase-locked with the reference clock provided by the CRF stream. There are 2 different roles of systems which participate in CRF data exchange. A system can either be a CRF Talker, which samples it's own clock and generates a stream of timestamps to transmit over the network, or a CRF Listener, the system which receives the generated timestamps and recovers the media clock from the timestamps. It then adjusts it's own clock to align with recovered media clock. The timestamps generated by the talker may not be continuous and the listener might have to interpolate some timestamps to recover the media clock. The number of timestamps to interpolate is mentioned in the CRF stream AVTPDU (Refer IEEE 1722-2016 Section 10.4 for AVTPDU structure). Only CRF Listener has been implemented in this commit. The CRF Sync element will create a separate thread to listen for the CRF stream. This thread will calculate and store the average period of the recovered media clock. The pipeline thread will use this stored period along with the first timestamp of the latest CRF AVTPDU received to calculate adjustment for timestamps in the audio/video streams. In case of CRF AVTPDUs with single timestamp, two consecutive CRF AVTPDUs will be used to figure out the average period of the recovered media clock. In case of H264 streams, both AVTP timestamp and H264 timestamp will be adjusted. In the future commits, another "CRF Checker" element will be introduced which will validate the timestamps on the AVTP Listener side. Which is why a lot of code has been implemented as part of the gstcrfbase class.
249 lines
7.6 KiB
C
249 lines
7.6 KiB
C
/*
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* GStreamer AVTP Plugin
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* Copyright (C) 2019 Intel Corporation
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
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* Boston, MA 02110-1301, USA.
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*/
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/**
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* SECTION:element-avtpcrfsync
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* @see_also: avtpcrfcheck
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*
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* Adjust the Presentation Time from AVTPDUs to align with the reference clock
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* provided by the CRF stream. For detailed information see chapter 10 in
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* https://standards.ieee.org/standard/1722-2016.html. A helpful aid for
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* visualizing CRF and it's advantages can be found at
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* http://grouper.ieee.org/groups/1722/contributions/2014/1722a-rsilfvast-Diagrams%20for%20Common%20Timing%20Grid%20and%20Presentation%20Time%20(for%20review%20and%20discussion).pdf
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* (Look at page 1).
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*
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* <refsect2>
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* <title>Example pipeline</title>
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* |[
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* gst-launch-1.0 audiotestsrc ! audioconvert ! avtpaafpay ! avtpcrfsync ! avtpsink
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* ]| This example pipeline will adjust the timestamps for rawaudio payload.
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* Refer to the avtpcrfcheck example to validate the adjusted timestamp.
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* </refsect2>
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*/
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#include <avtp.h>
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#include <avtp_aaf.h>
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#include <avtp_crf.h>
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#include <avtp_cvf.h>
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#include <glib.h>
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#include <math.h>
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#include "gstavtpcrfbase.h"
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#include "gstavtpcrfsync.h"
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#include "gstavtpcrfutil.h"
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GST_DEBUG_CATEGORY_STATIC (avtpcrfsync_debug);
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#define GST_CAT_DEFAULT (avtpcrfsync_debug)
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#define gst_avtp_crf_sync_parent_class parent_class
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G_DEFINE_TYPE (GstAvtpCrfSync, gst_avtp_crf_sync, GST_TYPE_AVTP_CRF_BASE);
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static GstFlowReturn gst_avtp_crf_sync_transform_ip (GstBaseTransform * parent,
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GstBuffer * buffer);
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static void
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gst_avtp_crf_sync_class_init (GstAvtpCrfSyncClass * klass)
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{
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GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
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gst_element_class_set_static_metadata (element_class,
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"Clock Reference Format (CRF) Synchronizer",
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"Filter/Network/AVTP",
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"Synchronize Presentation Time from AVTPDUs so they are phase-locked with clock provided by CRF stream",
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"Vedang Patel <vedang.patel@intel.com>");
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GST_BASE_TRANSFORM_CLASS (klass)->transform_ip =
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GST_DEBUG_FUNCPTR (gst_avtp_crf_sync_transform_ip);
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GST_DEBUG_CATEGORY_INIT (avtpcrfsync_debug, "avtpcrfsync", 0,
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"CRF Synchronizer");
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}
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static void
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gst_avtp_crf_sync_init (GstAvtpCrfSync * avtpcrfsync)
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{
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/* Nothing to do here. */
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}
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static void
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set_avtp_tstamp (GstAvtpCrfSync * avtpcrfsync, struct avtp_stream_pdu *pdu,
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GstClockTime tstamp)
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{
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int res;
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guint32 type;
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res =
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avtp_pdu_get ((struct avtp_common_pdu *) pdu, AVTP_FIELD_SUBTYPE, &type);
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g_assert (res == 0);
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switch (type) {
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case AVTP_SUBTYPE_AAF:
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res = avtp_aaf_pdu_set (pdu, AVTP_AAF_FIELD_TIMESTAMP, tstamp);
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g_assert (res == 0);
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break;
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case AVTP_SUBTYPE_CVF:
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res = avtp_cvf_pdu_set (pdu, AVTP_CVF_FIELD_TIMESTAMP, tstamp);
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g_assert (res == 0);
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break;
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default:
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GST_ERROR_OBJECT (avtpcrfsync, "type 0x%x not supported.\n", type);
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break;
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}
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}
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static void
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set_avtp_mr_bit (GstAvtpCrfSync * avtpcrfsync, struct avtp_stream_pdu *pdu,
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guint64 mr)
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{
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int res;
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guint32 type;
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res =
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avtp_pdu_get ((struct avtp_common_pdu *) pdu, AVTP_FIELD_SUBTYPE, &type);
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g_assert (res == 0);
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switch (type) {
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case AVTP_SUBTYPE_AAF:
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res = avtp_aaf_pdu_set (pdu, AVTP_AAF_FIELD_MR, mr);
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g_assert (res == 0);
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break;
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case AVTP_SUBTYPE_CVF:
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res = avtp_cvf_pdu_set (pdu, AVTP_CVF_FIELD_MR, mr);
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g_assert (res == 0);
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break;
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default:
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GST_ERROR_OBJECT (avtpcrfsync, "type 0x%x not supported.\n", type);
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break;
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}
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}
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static GstFlowReturn
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gst_avtp_crf_sync_transform_ip (GstBaseTransform * parent, GstBuffer * buffer)
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{
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GstClockTime tstamp, h264_time = 0, adjusted_tstamp, adjusted_h264_time = 0;
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GstAvtpCrfBase *avtpcrfbase = GST_AVTP_CRF_BASE (parent);
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GstAvtpCrfSync *avtpcrfsync = GST_AVTP_CRF_SYNC (avtpcrfbase);
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GstAvtpCrfThreadData *thread_data = &avtpcrfbase->thread_data;
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GstClockTime current_ts = thread_data->current_ts;
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gdouble avg_period = thread_data->average_period;
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struct avtp_stream_pdu *pdu;
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gboolean h264_packet;
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GstMapInfo info;
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gboolean res;
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if (!avg_period || !current_ts)
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return GST_FLOW_OK;
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res = gst_buffer_map (buffer, &info, GST_MAP_READWRITE);
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if (!res) {
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GST_ELEMENT_ERROR (avtpcrfsync, RESOURCE, OPEN_WRITE,
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("cannot access buffer"), (NULL));
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return GST_FLOW_ERROR;
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}
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if (!buffer_size_valid (&info)) {
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GST_DEBUG_OBJECT (avtpcrfsync, "Malformed AVTPDU, discarding it");
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goto exit;
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}
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pdu = (struct avtp_stream_pdu *) info.data;
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h264_packet = h264_tstamp_valid (pdu);
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if (h264_packet) {
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res = avtp_cvf_pdu_get (pdu, AVTP_CVF_FIELD_H264_TIMESTAMP, &h264_time);
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g_assert (res == 0);
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/*
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* Extrapolate H264 tstamp to 64 bit and assume it's greater than CRF
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* timestamp.
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*/
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h264_time |= current_ts & 0xFFFFFFFF00000000;
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if (h264_time < current_ts)
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h264_time += (1ULL << 32);
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/*
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* float typecasted to guint64 truncates the decimal part. So, round() it
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* before casting.
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*/
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adjusted_h264_time =
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(GstClockTime) roundl (current_ts + ceill (((gdouble) h264_time -
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current_ts) / avg_period) * avg_period);
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res =
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avtp_cvf_pdu_set (pdu, AVTP_CVF_FIELD_H264_TIMESTAMP,
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adjusted_h264_time);
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g_assert (res == 0);
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GST_LOG_OBJECT (avtpcrfsync,
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"Adjust H264 timestamp in CVF packet. tstamp: %" G_GUINT64_FORMAT
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" adjusted_tstamp: %" G_GUINT64_FORMAT,
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h264_time & 0xFFFFFFFF, adjusted_h264_time & 0xFFFFFFFF);
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}
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tstamp = get_avtp_tstamp (avtpcrfbase, pdu);
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if (tstamp == GST_CLOCK_TIME_NONE)
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goto exit;
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/*
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* Extrapolate the 32-bit AVTP Timestamp to 64-bit and assume it's greater
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* than the 64-bit CRF timestamp.
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*/
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tstamp |= current_ts & 0xFFFFFFFF00000000;
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if (tstamp < current_ts)
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tstamp += (1ULL << 32);
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/*
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* float typecasted to guint64 truncates the decimal part. So, round() it
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* before casting.
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*/
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adjusted_tstamp =
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(GstClockTime) roundl (current_ts + ceill ((tstamp -
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current_ts) / avg_period) * avg_period);
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set_avtp_tstamp (avtpcrfsync, pdu, adjusted_tstamp);
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set_avtp_mr_bit (avtpcrfsync, pdu, thread_data->mr);
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GST_LOG_OBJECT (avtpcrfsync,
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"Adjust AVTP timestamp. tstamp: %" G_GUINT64_FORMAT
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" Adjusted tstamp: %" G_GUINT64_FORMAT,
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tstamp & 0xFFFFFFFF, adjusted_tstamp & 0xFFFFFFFF);
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/*
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* Since we adjusted the AVTP/H264 presentation times in the AVTPDU, we also
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* need to adjust buffer times by the same amount so that the buffer is
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* transmitted at the right time.
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*/
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if (h264_packet) {
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if (GST_BUFFER_DTS (buffer) != GST_CLOCK_TIME_NONE)
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GST_BUFFER_DTS (buffer) += adjusted_tstamp - tstamp;
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GST_BUFFER_PTS (buffer) += adjusted_h264_time - h264_time;
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} else {
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GST_BUFFER_PTS (buffer) += adjusted_tstamp - tstamp;
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}
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exit:
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gst_buffer_unmap (buffer, &info);
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return GST_FLOW_OK;
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}
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gboolean
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gst_avtp_crf_sync_plugin_init (GstPlugin * plugin)
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{
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return gst_element_register (plugin, "avtpcrfsync", GST_RANK_NONE,
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GST_TYPE_AVTP_CRF_SYNC);
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}
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