Fix streaming from the middle of the file.

Telegram/SourceFiles/data/data_document.cpp

@@ -326,6 +326,7 @@ void StartStreaming(
 
 		auto options = Media::Streaming::PlaybackOptions();
 		options.speed = 1.;
+		options.position = (document->duration() / 2) * crl::time(1000);
 		player->init(options);
 		player->updates(
 		) | rpl::start_with_next_error_done([=](Update &&update) {

Telegram/SourceFiles/media/streaming/media_streaming_audio_track.cpp

@@ -25,7 +25,8 @@ AudioTrack::AudioTrack(
 , _stream(std::move(stream))
 , _audioId(audioId)
 , _ready(std::move(ready))
-, _error(std::move(error)) {
+, _error(std::move(error))
+, _playPosition(options.position) {
 	Expects(_ready != nullptr);
 	Expects(_error != nullptr);
 	Expects(_audioId.playId() != 0);

Telegram/SourceFiles/media/streaming/media_streaming_audio_track.h

@@ -69,6 +69,8 @@ private:
 
 	// Accessed from the main thread.
 	base::Subscription _subscription;
+	// First set from the same unspecified thread before _ready is called.
+	// After that accessed from the main thread.
 	rpl::variable<crl::time> _playPosition;
 
 };

Telegram/SourceFiles/media/streaming/media_streaming_loader_mtproto.cpp

@@ -138,6 +138,13 @@ void LoaderMtproto::cancelRequestsBefore(int offset) {
 		_sender.requestCanceller(),
 		&base::flat_map<int, mtpRequestId>::value_type::second);
 	_requests.erase(from, till);
+
+	if (!_requests.empty() && _requests.front().first > offset) {
+		ranges::for_each(
+			base::take(_requests),
+			_sender.requestCanceller(),
+			&base::flat_map<int, mtpRequestId>::value_type::second);
+	}
 }
 
 } // namespace Streaming

Telegram/SourceFiles/media/streaming/media_streaming_video_track.cpp

@@ -280,7 +280,9 @@ VideoTrackObject::TrackTime VideoTrackObject::trackTime() const {
 	const auto correction = _audioId.playId()
 		? Media::Player::mixer()->getVideoTimeCorrection(_audioId)
 		: Media::Player::Mixer::TimeCorrection();
-	const auto knownValue = correction ? correction.audioPositionValue : 0;
+	const auto knownValue = correction
+		? correction.audioPositionValue
+		: _startedPosition;
 	const auto knownTime = correction
 		? correction.audioPositionTime
 		: _startedTime;
@@ -288,8 +290,7 @@ VideoTrackObject::TrackTime VideoTrackObject::trackTime() const {
 	const auto sinceKnown = (worldNow - knownTime);
 
 	result.worldNow = worldNow;
-	result.trackNow = _startedPosition
-		+ knownValue
+	result.trackNow = knownValue
 		+ crl::time(std::round(sinceKnown * _options.speed));
 	return result;
 }