replace incoming absolute timestamps of any source (#5081)

Absolute timestamps are used to generate recording segments, so users
should not be able to change them, unless explicitly allowed.

Parameter useAbsoluteTimestamp allowed to re-enable absolute timestamps
with RTSP and WebRTC, now it is extended to all protocols.

docs/2-usage/14-route-absolute-timestamps.md

@@ -3,8 +3,8 @@
 Some streaming protocols allow to route absolute timestamps, associated with each frame, that are useful for synchronizing several video or data streams together. In particular, _MediaMTX_ supports receiving absolute timestamps with the following protocols and devices:
 
 - HLS
-- RTSP (when the `useAbsoluteTimestamp` parameter is `true`)
-- WebRTC (when the `useAbsoluteTimestamp` parameter is `true`)
+- RTSP
+- WebRTC
 - Raspberry Pi Camera
 
 and supports sending absolute timestamps with the following protocols:
@@ -13,6 +13,14 @@ and supports sending absolute timestamps with the following protocols:
 - RTSP
 - WebRTC
 
+By default, absolute timestamps of incoming frames are not used, instead they are replaced with the current timestamp. This prevents users from arbitrarily changing recording dates, and also allows to support sources that do not send absolute timestamps. It is possible to preserve original absolute timestamps by toggling the `useAbsoluteTimestamp` parameter:
+
+```yml
+pathDefaults:
+  # Use absolute timestamp of frames, instead of replacing them with the current time.
+  useAbsoluteTimestamp: false
+```
+
 ## Absolute timestamp in HLS
 
 In the HLS protocol, absolute timestamps are routed by adding a `EXT-X-PROGRAM-DATE-TIME` tag before each segment:

internal/protocols/hls/to_stream.go

@@ -8,6 +8,7 @@ import (
 	"github.com/bluenviron/gohlslib/v2/pkg/codecs"
 	"github.com/bluenviron/gortsplib/v5/pkg/description"
 	"github.com/bluenviron/gortsplib/v5/pkg/format"
+	"github.com/bluenviron/mediamtx/internal/conf"
 	"github.com/bluenviron/mediamtx/internal/logger"
 	"github.com/bluenviron/mediamtx/internal/ntpestimator"
 	"github.com/bluenviron/mediamtx/internal/stream"
@@ -20,7 +21,7 @@ const (
 	ntpStateInitial ntpState = iota
 	ntpStateUnavailable
 	ntpStateAvailable
-	ntpStateDegraded
+	ntpStateReplace
 )
 
 func multiplyAndDivide(v, m, d int64) int64 {
@@ -33,11 +34,16 @@ func multiplyAndDivide(v, m, d int64) int64 {
 func ToStream(
 	c *gohlslib.Client,
 	tracks []*gohlslib.Track,
+	pathConf *conf.Path,
 	strm **stream.Stream,
 ) ([]*description.Media, error) {
 	var ntpStat ntpState
 	var ntpStatMutex sync.Mutex
 
+	if !pathConf.UseAbsoluteTimestamp {
+		ntpStat = ntpStateReplace
+	}
+
 	var medias []*description.Media //nolint:prealloc
 
 	for _, track := range tracks {
@@ -69,11 +75,11 @@ func ToStream(
 				_, avail := c.AbsoluteTime(ctrack)
 				if avail {
 					(*strm).Parent.Log(logger.Warn, "absolute timestamp appeared after stream started, we are not using it")
-					ntpStat = ntpStateDegraded
+					ntpStat = ntpStateReplace
 				}
 				return ntpEstimator.Estimate(pts)
 
-			default: // ntpStateDegraded
+			default: // ntpStateReplace
 				return ntpEstimator.Estimate(pts)
 			}
 		}

internal/protocols/hls/to_stream_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/bluenviron/gortsplib/v5/pkg/description"
 	"github.com/bluenviron/gortsplib/v5/pkg/format"
 	"github.com/bluenviron/mediacommon/v2/pkg/formats/mpegts"
+	"github.com/bluenviron/mediamtx/internal/conf"
 	"github.com/bluenviron/mediamtx/internal/stream"
 	"github.com/bluenviron/mediamtx/internal/test"
 	"github.com/bluenviron/mediamtx/internal/unit"
@@ -18,7 +19,7 @@ import (
 )
 
 func TestToStreamNoSupportedCodecs(t *testing.T) {
-	_, err := ToStream(nil, []*gohlslib.Track{}, nil)
+	_, err := ToStream(nil, []*gohlslib.Track{}, &conf.Path{}, nil)
 	require.Equal(t, ErrNoSupportedCodecs, err)
 }
 
@@ -92,8 +93,11 @@ func TestToStream(t *testing.T) {
 	c = &gohlslib.Client{
 		URI: "http://localhost:5781/stream.m3u8",
 		OnTracks: func(tracks []*gohlslib.Track) error {
-			medias, err2 := ToStream(c, tracks, &strm)
+			medias, err2 := ToStream(c, tracks, &conf.Path{
+				UseAbsoluteTimestamp: true,
+			}, &strm)
 			require.NoError(t, err2)
+
 			require.Equal(t, []*description.Media{{
 				Type: description.MediaTypeVideo,
 				Formats: []format.Format{&format.H264{

internal/staticsources/hls/source.go

@@ -94,7 +94,7 @@ func (s *Source) Run(params defs.StaticSourceRunParams) error {
 			decodeErrors.Increase()
 		},
 		OnTracks: func(tracks []*gohlslib.Track) error {
-			medias, err2 := hls.ToStream(c, tracks, &stream)
+			medias, err2 := hls.ToStream(c, tracks, params.Conf, &stream)
 			if err2 != nil {
 				return err2
 			}

mediamtx.yml

@@ -482,7 +482,7 @@ pathDefaults:
   # If the stream is not available, redirect readers to this path.
   # It can be can be a relative path (i.e. /otherstream) or an absolute RTSP URL.
   fallback:
-  # Route original absolute timestamps of RTSP and WebRTC frames, instead of replacing them.
+  # Use absolute timestamp of frames, instead of replacing them with the current time.
   useAbsoluteTimestamp: false
 
   ###############################################