MediaController’s play_media should not set current_time to 0 by default

[andrewshadura]

The documentation for the Load command says currentTime is optional:

Seconds since beginning of content. If the content is live content, and position is not specifed, the stream will start at the live position

This is vital to the ability to cast live streams and is not currently possible without deriving a separate controller overriding play_media. Please consider defaulting to None e.g. in this manner:

diff --git a/pychromecast/controllers/media.py b/pychromecast/controllers/media.py
index cc47db4..54f9904 100644
--- a/pychromecast/controllers/media.py
+++ b/pychromecast/controllers/media.py
@@ -492,7 +492,7 @@ class MediaController(BaseController):
         content_type,
         title=None,
         thumb=None,
-        current_time=0,
+        current_time=None,
         autoplay=True,
         stream_type=STREAM_TYPE_BUFFERED,
         metadata=None,
@@ -560,7 +560,7 @@ class MediaController(BaseController):
         content_type,
         title=None,
         thumb=None,
-        current_time=0,
+        current_time=None,
         autoplay=True,
         stream_type=STREAM_TYPE_BUFFERED,
         metadata=None,
@@ -628,7 +628,8 @@ class MediaController(BaseController):
                 "media": media,
                 MESSAGE_TYPE: TYPE_LOAD,
             }
-        msg["currentTime"] = current_time
+        if current_time is not None:
+            msg["currentTime"] = current_time
         msg["autoplay"] = autoplay
         msg["customData"] = {}

[emontnemery]

This seems reasonable enough, can you please explain what difference it makes though?
Do you want to deduce if it's live media by testing if current_time is None?

[andrewshadura]

No, I want to be able to play the live stream at the live stream position, not at two or three hours in the past (which is what 0 corresponds to).

[andrewshadura]

When I’m playing live TV streams, None plays what’s currently being aired, 0 plays the recording of however much the TV stream allows to seek into the past, in my case it’s about three hours.

[emontnemery]

OK. To make this a non-breaking change, I think the following change is enough, i.e. no change of default values:

                 "media": media,
                 MESSAGE_TYPE: TYPE_LOAD,
             }
-        msg["currentTime"] = current_time
+        if current_time is not None:
+            msg["currentTime"] = current_time
         msg["autoplay"] = autoplay
         msg["customData"] = {}

[andrewshadura]

I disagree: it makes more sense to make the default value the same as what the protocol specifies. It is not going to break anything since live TV streams didn't work anyway, anyone who wanted to watch the recording were likely passing an explicit zero already and the rest just used the cases where it didn't matter.

[emontnemery]

For a non live stream, does not setting currentTime have the same result as setting it to 0?

[andrewshadura]

I believe so; non-live contents starts playing from the beginning.

[emontnemery]

Can you give some examples of live streams where you see the problem (for testing)?

[emontnemery]

To be clear: Since what you propose is a breaking change, I'd really like to have some examples of live streams where setting currentTime to 0 starts playback from the past as you explain. Would that be possible?

[andrewshadura]

I’m afraid I’m not able to share the link since it’s not a public stream, and I’ve not tried watching other TV streams to be honest.

I don’t understand why you consider this a breaking change: watching live TV streams with a "backlog" didn’t work before but will work with this change, nothing else is affected by it.

[andrewshadura]

Okay, found you a public stream where this behaviour can be observed: http://mfe.cliptv.az/dash/BBC_World_News_SD.ism/playlist.mpd

Here, the live stream is playing on the laptop, and the current_time=0 is playing on the Chromecast:

[andrewshadura]

It’s not two or three hours difference, as with my other non-public stream, but a difference nevertheless.

[emontnemery]

Thanks!

Can you please explain again why what I proposed here is not good enough: #439 (comment)
What's the use case where it's not acceptable to pass None to currentTime (aside from the default behavior being more reasonable with the change)?

[andrewshadura]

It is acceptable, but I don’t understand why keep incorrect default behaviour (which goes against the spec) which I doubt anything depends on? What worked before, will still work since non-live videos default to 0 anyway.

[andrewshadura]

If you want even better compatibility, feel free to make it depend on the resource type being a live stream.

[emontnemery]

Thanks for the patience, implemented in #446