The existing code assumed that the first frame received by the decklink output would always be PTS zero. However if running in other timing modes than the default of CBR, items such as frame dropping at the beginning may result in starting at a non-zero PTS. For example, in our setup because we discard probing data and run with "-vsync 2" the first video frame scheduled to the decklink output will have a PTS around 170. Scheduling frames too far into the future will either fail or cause a backlog of frames scheduled far enough into the future that the entire pipeline will stall. Issue can be reproduced with the following command-line: ./ffmpeg -copyts -i foo.ts -f decklink -vcodec v210 -ac 2 'DeckLink Duo (4)' Keep track of the PTS of the first frame received, so that when we enable start playback we can provide that value to the decklink driver. Thanks to Marton Balint for review and suggestion to use AV_NOPTS_VALUE rather than zero for the initial value.
Showing the changes to libavdevice/decklink_enc.cpp (1 of 2 files). Show all
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| @@ -486,6 +486,9 @@ static int decklink_write_video_packet(AVFormatContext *avctx, AVPacket *pkt) · 485 unmodified lines | |||
| 486 | ctx->frames_buffer_available_spots--; | 486 | ctx->frames_buffer_available_spots--; |
| 487 | pthread_mutex_unlock(&ctx->mutex); | 487 | pthread_mutex_unlock(&ctx->mutex); |
| 488 | 488 | ||
| 489 | if (ctx->first_pts == AV_NOPTS_VALUE) | ||
| 490 | ctx->first_pts = pkt->pts; | ||
| 491 | |||
| 489 | /* Schedule frame for playback. */ | 492 | /* Schedule frame for playback. */ |
| 490 | hr = ctx->dlo->ScheduleVideoFrame((class IDeckLinkVideoFrame *) frame, | 493 | hr = ctx->dlo->ScheduleVideoFrame((class IDeckLinkVideoFrame *) frame, |
| 491 | pkt->pts * ctx->bmd_tb_num, | 494 | pkt->pts * ctx->bmd_tb_num, |
| @@ -505,14 +508,14 @@ static int decklink_write_video_packet(AVFormatContext *avctx, AVPacket *pkt) · 13 unmodified lines | |||
| 505 | " Video may misbehave!\n"); | 508 | " Video may misbehave!\n"); |
| 506 | 509 | ||
| 507 | /* Preroll video frames. */ | 510 | /* Preroll video frames. */ |
| 508 | if (!ctx->playback_started && pkt->pts > ctx->frames_preroll) { | 511 | if (!ctx->playback_started && pkt->pts > (ctx->first_pts + ctx->frames_preroll)) { |
| 509 | av_log(avctx, AV_LOG_DEBUG, "Ending audio preroll.\n"); | 512 | av_log(avctx, AV_LOG_DEBUG, "Ending audio preroll.\n"); |
| 510 | if (ctx->audio && ctx->dlo->EndAudioPreroll() != S_OK) { | 513 | if (ctx->audio && ctx->dlo->EndAudioPreroll() != S_OK) { |
| 511 | av_log(avctx, AV_LOG_ERROR, "Could not end audio preroll!\n"); | 514 | av_log(avctx, AV_LOG_ERROR, "Could not end audio preroll!\n"); |
| 512 | return AVERROR(EIO); | 515 | return AVERROR(EIO); |
| 513 | } | 516 | } |
| 514 | av_log(avctx, AV_LOG_DEBUG, "Starting scheduled playback.\n"); | 517 | av_log(avctx, AV_LOG_DEBUG, "Starting scheduled playback.\n"); |
| 515 | if (ctx->dlo->StartScheduledPlayback(0, ctx->bmd_tb_den, 1.0) != S_OK) { | 518 | if (ctx->dlo->StartScheduledPlayback(ctx->first_pts * ctx->bmd_tb_num, ctx->bmd_tb_den, 1.0) != S_OK) { |
| 516 | av_log(avctx, AV_LOG_ERROR, "Could not start scheduled playback!\n"); | 519 | av_log(avctx, AV_LOG_ERROR, "Could not start scheduled playback!\n"); |
| 517 | return AVERROR(EIO); | 520 | return AVERROR(EIO); |
| 518 | } | 521 | } |
| @@ -559,6 +562,7 @@ av_cold int ff_decklink_write_header(AVFormatContext *avctx) · 40 unmodified lines | |||
| 559 | ctx->list_formats = cctx->list_formats; | 562 | ctx->list_formats = cctx->list_formats; |
| 560 | ctx->preroll = cctx->preroll; | 563 | ctx->preroll = cctx->preroll; |
| 561 | ctx->duplex_mode = cctx->duplex_mode; | 564 | ctx->duplex_mode = cctx->duplex_mode; |
| 565 | ctx->first_pts = AV_NOPTS_VALUE; | ||
| 562 | if (cctx->link > 0 && (unsigned int)cctx->link < FF_ARRAY_ELEMS(decklink_link_conf_map)) | 566 | if (cctx->link > 0 && (unsigned int)cctx->link < FF_ARRAY_ELEMS(decklink_link_conf_map)) |
| 563 | ctx->link = decklink_link_conf_map[cctx->link]; | 567 | ctx->link = decklink_link_conf_map[cctx->link]; |
| 564 | cctx->ctx = ctx; | 568 | cctx->ctx = ctx; |