From af680761cf7c3e97660e8e55c68f42e90b026bf9 Mon Sep 17 00:00:00 2001 From: Carl Hetherington Date: Sun, 2 Aug 2020 22:24:05 +0200 Subject: [PATCH] Detect soft 2:3 pulldown (telecine) files and decode them at 23.976. DVD rips from NTSC DVDs are sometimes (always?) encoded using soft 2:3 pulldown. The video frames are actually 23.976 but FFmpeg detects them as 29.97. With the current approach of the video decoder ignoring most PTSs and assuming a constant frame rate it is vital that the file contains the number of frames per second that the detected frame rate predicts. This fixes large sync errors with NTSC DVD rips (#1790). --- src/lib/ffmpeg_content.cc | 8 ++++++++ src/lib/ffmpeg_examiner.cc | 38 ++++++++++++++++++++++++++++++++++---- src/lib/ffmpeg_examiner.h | 7 ++++++- 3 files changed, 48 insertions(+), 5 deletions(-) diff --git a/src/lib/ffmpeg_content.cc b/src/lib/ffmpeg_content.cc index f3c0d01cb..1fb95535f 100644 --- a/src/lib/ffmpeg_content.cc +++ b/src/lib/ffmpeg_content.cc @@ -337,6 +337,14 @@ FFmpegContent::examine (shared_ptr film, shared_ptr job) set_default_colour_conversion (); } + if (examiner->has_video() && examiner->pulldown() && video_frame_rate() && fabs(*video_frame_rate() - 29.97) < 0.001) { + /* FFmpeg has detected this file as 29.97 and the examiner thinks it is using "soft" 2:3 pulldown (telecine). + * This means we can treat it as a 23.976fps file. + */ + set_video_frame_rate (24000.0 / 1001); + video->set_length (video->length() * 24.0 / 30); + } + #ifdef DCPOMATIC_VARIANT_SWAROOP _id = examiner->id (); #endif diff --git a/src/lib/ffmpeg_examiner.cc b/src/lib/ffmpeg_examiner.cc index cc6a62ff6..87bb8ce95 100644 --- a/src/lib/ffmpeg_examiner.cc +++ b/src/lib/ffmpeg_examiner.cc @@ -18,6 +18,7 @@ */ +#include "dcpomatic_log.h" #include "ffmpeg_examiner.h" #include "ffmpeg_content.h" #include "job.h" @@ -43,16 +44,24 @@ DCPOMATIC_ENABLE_WARNINGS using std::string; using std::cout; using std::max; +using std::vector; using boost::shared_ptr; using boost::optional; using namespace dcpomatic; +/* This is how many frames from the start of any video that we will examine to see if we + * can spot soft 2:3 pull-down ("telecine"). + */ +static const int PULLDOWN_CHECK_FRAMES = 16; + + /** @param job job that the examiner is operating in, or 0 */ FFmpegExaminer::FFmpegExaminer (shared_ptr c, shared_ptr job) : FFmpeg (c) , _video_length (0) , _need_video_length (false) + , _pulldown (false) { /* Find audio and subtitle streams */ @@ -106,9 +115,15 @@ DCPOMATIC_DISABLE_WARNINGS /* Run through until we find: * - the first video. * - the first audio for each stream. + * - the top-field-first and repeat-first-frame values ("temporal_reference") for the first PULLDOWN_CHECK_FRAMES video frames. */ int64_t const len = _file_group.length (); + /* A string which we build up to describe the top-field-first and repeat-first-frame values for the first few frames. + * It would be nicer to use something like vector here but we want to search the array for a pattern later, + * and a string seems a reasonably neat way to do that. + */ + string temporal_reference; while (true) { int r = av_read_frame (_format_context, &_packet); if (r < 0) { @@ -127,7 +142,7 @@ DCPOMATIC_DISABLE_WARNINGS DCPOMATIC_ENABLE_WARNINGS if (_video_stream && _packet.stream_index == _video_stream.get()) { - video_packet (context); + video_packet (context, temporal_reference); } bool got_all_audio = true; @@ -143,7 +158,7 @@ DCPOMATIC_ENABLE_WARNINGS av_packet_unref (&_packet); - if (_first_video && got_all_audio) { + if (_first_video && got_all_audio && temporal_reference.size() >= PULLDOWN_CHECK_FRAMES) { /* All done */ break; } @@ -173,6 +188,13 @@ DCPOMATIC_ENABLE_WARNINGS DCPOMATIC_ASSERT (fabs (*_rotation - 90 * round (*_rotation / 90)) < 2); } + LOG_GENERAL("Temporal reference was %1", temporal_reference); + if (temporal_reference.find("T2T3B2B3T2T3B2B3") || temporal_reference.find("B2B3T2T3B2B3T2T3")) { + /* The magical sequence (taken from mediainfo) suggests that 2:3 pull-down is in use */ + _pulldown = true; + LOG_GENERAL_NC("Suggest that this may be 2:3 pull-down (soft telecine)"); + } + #ifdef DCPOMATIC_VARIANT_SWAROOP AVDictionaryEntry* e = av_dict_get (_format_context->metadata, SWAROOP_ID_TAG, 0, 0); if (e) { @@ -182,12 +204,16 @@ DCPOMATIC_ENABLE_WARNINGS } +/** @param temporal_reference A string to which we should add two characters per frame; + * the first is T or B depending on whether it's top- or bottom-field first, + * ths seconds is 3 or 2 depending on whether "repeat_pict" is true or not. + */ void -FFmpegExaminer::video_packet (AVCodecContext* context) +FFmpegExaminer::video_packet (AVCodecContext* context, string& temporal_reference) { DCPOMATIC_ASSERT (_video_stream); - if (_first_video && !_need_video_length) { + if (_first_video && !_need_video_length && temporal_reference.size() >= PULLDOWN_CHECK_FRAMES) { return; } @@ -203,6 +229,10 @@ DCPOMATIC_ENABLE_WARNINGS _format_context->streams[_video_stream.get()] ).get_value_or (ContentTime ()).frames_round (video_frame_rate().get ()); } + if (temporal_reference.size() < PULLDOWN_CHECK_FRAMES) { + temporal_reference += (_frame->top_field_first ? "T" : "B"); + temporal_reference += (_frame->repeat_pict ? "3" : "2"); + } } } diff --git a/src/lib/ffmpeg_examiner.h b/src/lib/ffmpeg_examiner.h index 9ffb8421b..4f5110ca0 100644 --- a/src/lib/ffmpeg_examiner.h +++ b/src/lib/ffmpeg_examiner.h @@ -77,6 +77,10 @@ public: return _rotation; } + bool pulldown () const { + return _pulldown; + } + #ifdef DCPOMATIC_VARIANT_SWAROOP boost::optional id () const { return _id; @@ -84,7 +88,7 @@ public: #endif private: - void video_packet (AVCodecContext *); + void video_packet (AVCodecContext *, std::string& temporal_reference); void audio_packet (AVCodecContext *, boost::shared_ptr); std::string stream_name (AVStream* s) const; @@ -101,6 +105,7 @@ private: bool _need_video_length; boost::optional _rotation; + bool _pulldown; #ifdef DCPOMATIC_VARIANT_SWAROOP boost::optional _id; -- 2.30.2