From 2aef9000a1c8d76d3072365ffcb471ebffa20d3d Mon Sep 17 00:00:00 2001
From: Andreas Schneider <asn@cryptomilk.org>
Date: Tue, 15 Mar 2022 14:26:16 +0100
Subject: [PATCH] Track first_dts instead of using non-upstream functions

The function av_stream_get_first_dts() is not an upstream ffmpeg function and
is not available if you build with system ffmpeg. We can easily track the
first_dts on our own.

See also
https://ffmpeg.org/pipermail/ffmpeg-devel/2021-September/285401.html

Bug: 1306560

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Change-Id: I90ba3cf2f2e16f56a0b405f26c67f911349fb71d
---
 media/filters/ffmpeg_demuxer.cc | 18 ++++++++++++------
 media/filters/ffmpeg_demuxer.h  |  3 +++
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
index 111899b661..799fc6e941 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -97,7 +97,7 @@ static base::TimeDelta FramesToTimeDelta(int frames, double sample_rate) {
                             sample_rate);
 }
 
-static base::TimeDelta ExtractStartTime(AVStream* stream) {
+static base::TimeDelta ExtractStartTime(AVStream* stream, int64_t first_dts) {
   // The default start time is zero.
   base::TimeDelta start_time;
 
@@ -107,12 +107,12 @@ static base::TimeDelta ExtractStartTime(AVStream* stream) {
 
   // Next try to use the first DTS value, for codecs where we know PTS == DTS
   // (excludes all H26x codecs). The start time must be returned in PTS.
-  if (av_stream_get_first_dts(stream) != kNoFFmpegTimestamp &&
+  if (first_dts != AV_NOPTS_VALUE &&
       stream->codecpar->codec_id != AV_CODEC_ID_HEVC &&
       stream->codecpar->codec_id != AV_CODEC_ID_H264 &&
       stream->codecpar->codec_id != AV_CODEC_ID_MPEG4) {
     const base::TimeDelta first_pts =
-        ConvertFromTimeBase(stream->time_base, av_stream_get_first_dts(stream));
+        ConvertFromTimeBase(stream->time_base, first_dts);
     if (first_pts < start_time)
       start_time = first_pts;
   }
@@ -283,6 +283,7 @@ FFmpegDemuxerStream::FFmpegDemuxerStream(
       fixup_negative_timestamps_(false),
       fixup_chained_ogg_(false),
       num_discarded_packet_warnings_(0),
+      first_dts_(AV_NOPTS_VALUE),
       last_packet_pos_(AV_NOPTS_VALUE),
       last_packet_dts_(AV_NOPTS_VALUE) {
   DCHECK(demuxer_);
@@ -349,6 +350,10 @@ void FFmpegDemuxerStream::EnqueuePacket(ScopedAVPacket packet) {
   int64_t packet_dts =
       packet->dts == AV_NOPTS_VALUE ? packet->pts : packet->dts;
 
+  if (first_dts_ == AV_NOPTS_VALUE) {
+    first_dts_ = packet_dts;
+  }
+
   // Chained ogg files have non-monotonically increasing position and time stamp
   // values, which prevents us from using them to determine if a packet should
   // be dropped. Since chained ogg is only allowed on single track audio only
@@ -1442,7 +1447,8 @@ void FFmpegDemuxer::OnFindStreamInfoDone(int result) {
 
     max_duration = std::max(max_duration, streams_[i]->duration());
 
-    base::TimeDelta start_time = ExtractStartTime(stream);
+    base::TimeDelta start_time =
+        ExtractStartTime(stream, streams_[i]->first_dts());
 
     // Note: This value is used for seeking, so we must take the true value and
     // not the one possibly clamped to zero below.
@@ -1599,7 +1605,7 @@ FFmpegDemuxerStream* FFmpegDemuxer::FindStreamWithLowestStartTimestamp(
   for (const auto& stream : streams_) {
     if (!stream || stream->IsEnabled() != enabled)
       continue;
-    if (av_stream_get_first_dts(stream->av_stream()) == kInvalidPTSMarker)
+    if (stream->first_dts() == AV_NOPTS_VALUE)
       continue;
     if (!lowest_start_time_stream ||
         stream->start_time() < lowest_start_time_stream->start_time()) {
@@ -1620,7 +1626,7 @@ FFmpegDemuxerStream* FFmpegDemuxer::FindPreferredStreamForSeeking(
     if (stream->type() != DemuxerStream::VIDEO)
       continue;
 
-    if (av_stream_get_first_dts(stream->av_stream()) == kInvalidPTSMarker)
+    if (stream->first_dts() == AV_NOPTS_VALUE)
       continue;
 
     if (!stream->IsEnabled())
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index c147309d6f..48a8f6ad8c 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -151,6 +151,8 @@ class MEDIA_EXPORT FFmpegDemuxerStream : public DemuxerStream {
   base::TimeDelta start_time() const { return start_time_; }
   void set_start_time(base::TimeDelta time) { start_time_ = time; }
 
+  int64_t first_dts() const { return first_dts_; }
+
  private:
   friend class FFmpegDemuxerTest;
 
@@ -208,6 +210,7 @@ class MEDIA_EXPORT FFmpegDemuxerStream : public DemuxerStream {
   bool fixup_chained_ogg_;
 
   int num_discarded_packet_warnings_;
+  int64_t first_dts_;
   int64_t last_packet_pos_;
   int64_t last_packet_dts_;
 };
-- 
2.35.1