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

[Devin Heitmueller]

Hi Matt,

Thanks for your contribution.  Comments inline.

On Mon, Jul 7, 2025 at 9:40 PM Matt via ffmpeg-devel
<ffmpeg-devel at ffmpeg.org> wrote:
> 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>

Not needed (see below)

>  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);
> +            }

The sleep calls should use av_usleep(), which is portable and you
don't need unistd.h.  Also, there should be some limit so that it
doesn't block forever if video frames are scheduled very far in the
future (e.g. after 1 second, give up and log a warning).

Devin

-- 
Devin Heitmueller, Senior Software Engineer
LTN Global Communications
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