[FFmpeg-devel] [PATCH] Playout to DeckLink will wait for all buffered frames before stopping.

[FFmpeg-devel] [PATCH] Playout to DeckLink will wait for all buffered frames before stopping.

[Matt via ffmpeg-devel]

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From: matthew@watchgood.com
To: ffmpeg-devel@ffmpeg.org
Cc: Matthew Rademaker <matthew@watchgood.com>
Subject: [PATCH] Playout to DeckLink will wait for all buffered frames before stopping.
Date: Tue,  8 Jul 2025 11:39:38 +1000
Message-ID: <20250708013949.3044652-1-matthew@watchgood.com>

From: Matthew Rademaker <matthew@watchgood.com>

Instead of stopping video output to the card as soon as encoding is
finished, wait until the card reports that all buffered frames have
been played out. Wait longer if there are more frames, shorter if
there are fewer so that we end ASAP.

See https://ffmpeg.org/pipermail/ffmpeg-devel/2025-March/340634.html

Signed-off-by: Matthew Rademaker <matthew@watchgood.com>
---
 libavdevice/decklink_enc.cpp | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/libavdevice/decklink_enc.cpp b/libavdevice/decklink_enc.cpp
index cb8f91730e..5751f27de8 100644
--- a/libavdevice/decklink_enc.cpp
+++ b/libavdevice/decklink_enc.cpp
@@ -20,6 +20,7 @@
  */

 #include <atomic>
+#include <unistd.h>
 using std::atomic;

 /* Include internal.h first to avoid conflict between winsock.h (used by
@@ -369,11 +370,26 @@ av_cold int ff_decklink_write_trailer(AVFormatContext *avctx)
 {
     struct decklink_cctx *cctx = (struct decklink_cctx *)avctx->priv_data;
     struct decklink_ctx *ctx = (struct decklink_ctx *)cctx->ctx;
+    uint32_t buffered;

     if (ctx->playback_started) {
         BMDTimeValue actual;
         ctx->dlo->StopScheduledPlayback(ctx->last_pts * ctx->bmd_tb_num,
                                         &actual, ctx->bmd_tb_den);
+        av_log(avctx, AV_LOG_DEBUG, "Stopped at %ld, requested %ld\n", actual, ctx->last_pts * ctx->bmd_tb_num);
+        while (1){
+            ctx->dlo->GetBufferedVideoFrameCount(&buffered);
+            if (buffered <= 0){
+                break;
+            }
+            av_log(avctx, AV_LOG_DEBUG, "Waiting for %d buffered frames to finish\n", buffered);
+            if (buffered < 5) {
+                usleep(1);
+            } else {
+                usleep(300);
+            }
+        }
+        av_log(avctx, AV_LOG_DEBUG, "All frames returned, finishing up\n");
         ctx->dlo->DisableVideoOutput();
         if (ctx->audio)
             ctx->dlo->DisableAudioOutput();
--
2.43.0


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