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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.
56 lines
1.8 KiB
C
56 lines
1.8 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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#ifndef __GST_AVTP_CRF_SYNC_H__
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#define __GST_AVTP_CRF_SYNC_H__
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#include <gst/gst.h>
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#include "gstavtpcrfbase.h"
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G_BEGIN_DECLS
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#define GST_TYPE_AVTP_CRF_SYNC (gst_avtp_crf_sync_get_type())
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#define GST_AVTP_CRF_SYNC(obj) \
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(G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_AVTP_CRF_SYNC,GstAvtpCrfSync))
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#define GST_AVTP_CRF_SYNC_CLASS(klass) \
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(G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_AVTP_CRF_SYNC,GstAvtpCrfSyncClass))
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#define GST_IS_AVTP_CRF_SYNC(obj) \
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(G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_AVTP_CRF_SYNC))
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#define GST_IS_AVTP_CRF_SYNC_CLASS(klass) \
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(G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_AVTP_CRF_SYNC))
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typedef struct _GstAvtpCrfSync GstAvtpCrfSync;
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typedef struct _GstAvtpCrfSyncClass GstAvtpCrfSyncClass;
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struct _GstAvtpCrfSync
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{
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GstAvtpCrfBase avtpcrfbase;
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};
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struct _GstAvtpCrfSyncClass
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{
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GstAvtpCrfBaseClass parent_class;
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};
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GType gst_avtp_crf_sync_get_type (void);
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gboolean gst_avtp_crf_sync_plugin_init (GstPlugin * plugin);
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G_END_DECLS
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#endif /* __GST_AVTP_CRF_SYNC_H__ */
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