From 4e1e8784aa254b16ca506001227450da66eaa2c3 Mon Sep 17 00:00:00 2001
From: Timothy Pearson <tpearson@raptorengineering.com>
Date: Mon, 25 Nov 2019 17:30:39 -0600
Subject: Add support for ALSA link timestamps

This allows certain drivers, such as the Raptor/Magewell ProCapture PerfectSync driver stack, to guarantee correct timestamps and A/V sync
---
 libavdevice/alsa_dec.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/libavdevice/alsa_dec.c b/libavdevice/alsa_dec.c
index 0b3b7e4..f59b043 100644
--- a/libavdevice/alsa_dec.c
+++ b/libavdevice/alsa_dec.c
@@ -131,18 +131,30 @@ static int audio_read_packet(AVFormatContext *s1, AVPacket *pkt)
     dts = 0;
 #if HAVE_ALSA_HR_TS
     if (s->use_driver_timestamps) {
-        tstamp_config.type_requested = 1;
+        if (s->use_driver_timestamps & 4) {
+            tstamp_config.type_requested = 2;
+        }
+        else {
+          tstamp_config.type_requested = 1;
+        }
         tstamp_config.report_delay = 1;
         snd_pcm_status_set_audio_htstamp_config(s->st, &tstamp_config);
         if (snd_pcm_status(s->h, s->st) >= 0) {
             struct timespec ts;
-            snd_pcm_status_get_driver_htstamp(s->st, &ts);
+            if (s->use_driver_timestamps & 4) {
+                snd_pcm_status_get_audio_htstamp(s->st, &ts);
+                delay = 0;
+            }
             if ((ts.tv_sec == 0) && (ts.tv_nsec == 0)) {
-                // Try alternate access method
+                // Try alternate access method #1
+              snd_pcm_status_get_driver_htstamp(s->st, &ts);
+            }
+            if ((ts.tv_sec == 0) && (ts.tv_nsec == 0)) {
+                // Try alternate access method #2
                 snd_pcm_status_get_htstamp(s->st, &ts);
             }
-            dts = (int64_t)ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
             delay = snd_pcm_status_get_delay(s->st);
+            dts = (int64_t)ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
         }
     }
 #endif
@@ -152,9 +164,14 @@ static int audio_read_packet(AVFormatContext *s1, AVPacket *pkt)
         dts = av_gettime();
         snd_pcm_delay(s->h, &delay);
     }
-
     dts -= av_rescale(delay + res, 1000000, s->sample_rate);
-    pkt->pts = ff_timefilter_update(s->timefilter, dts, s->last_period);
+
+    if (s->use_driver_timestamps & 4) {
+        pkt->pts = dts;
+    }
+    else {
+        pkt->pts = ff_timefilter_update(s->timefilter, dts, s->last_period);
+    }
     s->last_period = res;
 
     pkt->size = res * s->frame_size;
-- 
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