20-60s buffering for LIVE media streaming & huge delay

[fornellas]

I've been debugging https://github.com/muammar/mkchromecast/issues/292, and traced the issue down to pychromecast / my Chromecast Audio.

Using examples/media_example.py, I was able to repro the issue. Here's the setup:

• Start this Flask server (FLASK_APP=pacast.py flask run --host=0.0.0.0).
  • It will spin parec & ffmpeg to stream captured audio.
• Use examples/media_example.py to connect the Chromecast to Flask.
  • Change play parameters to: cast.media_controller.play_media(args.url, "audio/aac", stream_type="LIVE").

We can then, see the delay:

• If Pulseaudio is quiet.
  • It gets stuck in BUFFERING for ~60s (~32k streamed), plays for ~1s, and back to BUFFERING.
• If Pulseaudio has output.
  • It gets stuck in BUFFERING for ~20s (~512k streamed), then switches to PLAYING.
  • Things play fine from this point on, but audio is 20s delayed.

Google documentation says that LIVE should work, but the described above behavior is the same with stream_type="BUFFERED".

If we try serving an MP3 from a URL for example, it starts playing within ~1s, as the Chromecast can fill its buffer pretty quick. I haven't tried, but I bet if we serve the MP3 file at 1kB/s, it'll buffer for the same 20s.

From all tests I did, data is being streamed from Flask to Chromecast in a reasonable amount of time, but Chromecast insists in buffer things (either 20s or 512k it seems) thus having a massive delay as a result.

Is there some Chromecast option we're missing to send for live streaming?

[muammar]

@fornellas thank you very much for your work here. I also look forward to knowing how to solve this issue.

[emontnemery]

Unfortunately, it seems LIVE is not working as expected for Chromecasts, as you have experienced the Chromecast device still buffers. A workaround is to send a "play" command after a few seconds of buffering, as discussed here: https://github.com/home-assistant/core/issues/16319#issuecomment-476351385 This works for some streams, but not all.

[muammar]

@emontnemery thanks for your reply. That is what I recently implemented and reduced the delay to ~6 seconds.

[fornellas]

@emontnemery I'll give the "play" hack a try when I find some time, tkz for the tip.

Do you happen to know if this issue happens with devices other than Chromecast Audio?

[pasikarkkainen]

I just did a few tests using Chrome and casting a tab which has some web audio player in it.. test result: hitting play/pause on the web audio player results in less than 1 second delay with the Chrome browser internal tab casting.

I tested with both Chromecast Ultra and Chromecast Audio devices. Similar less than 1 second delay/lag with both devices.

So yeah, definitely something wrong with the pychromecast LIVE mode..

[emontnemery]

@pasikarkkainen Right, but that is using the app "Chrome Audio Mirroring", not the builtin app "Default Media Receiver". The problem here is that "Default Media Receiver" buffers some live streams.

[clam-i-am]

@fornellas I opened this issue up on the catt issues board before I saw this. (catt appears to leverage pychromecast.) A few comments that may or may not be helpful...

In that issue I noticed a low bitrate live stream would undergo this "buffering" treatment for about 5 minutes before playing, while decent bitrate ones (e.g. 128kbps) would start up within 5-10 seconds. While my issue link above only shows output at a point in time, I can say that I too have seen the BUFFERING->PLAYING->immediately back to BUFFERING (if I re-run the info command in catt quickly enough).

Regarding your question "does this happen with other devices besides the Audio?" - I've see it on the Mini, Chromecast, and a Nest Hub, too. Same behavior across all.

Lastly, quickly triggering "play" for the buffering live stream has mixed results - doesn't appear to work with any consistency on this end.

[tjharman]

I agree, I have tried to work around this by triggering a "play" but it doesn't help. I can't figure out why some of my stations play straight away, and some take ages.

[Eerovil]

I've had success circumventing this problem by using another media controller app (BubbleUPNP).

The question remains, should we keep something like that as a completely separate app (callable in homeassistant via quick play), or perhaps add a global setting to pychromecast, where you could choose whatever "Media player app" you wish to use? I'll make a pull request with the quick_play feature for now.

EDIT: For some results: The stream I've tested with takes 20-25 seconds to start with the default player, but only 6 seconds with BubbleUPNP.

[emontnemery]

@Eerovil This sounds great! Does the Bubble UPNP work better then the default media receiver with all streams?

[Eerovil]

@emontnemery I couldn't say, since finding theses low-bitrate streams is pretty difficult. The stream used previously in the catt issue https://github.com/skorokithakis/catt/issues/264#issue-627857166 doesn't work anymore.

EDIT: It does work but there is rarely any audio. I'll try to see if I can get a measurement...

EDIT: Yup, something like 10 seconds for playback it seems. Not 100% sure though (I just restarted the stream when audio started coming)

[ankostis]

Thank you for yor efforts.

Just to mention that ~6sec with BubbleUPNP while still improving things, it does not seem like dealing with the problem.

Have you considered switching to an actual MPEG-DASH implementation, as muammar/mkchromecast#292 seems to suggest?

[emontnemery]

@ankostis who is the question for? pychromecast is not doing anything fancier than sending an URL to the Chromecast.

[Eerovil]

@ankostis If there is a Chromecast app with a better implementation (and also implements the media controller namespace) then surely using that is a better idea. You can use any app.

[ankostis]

pychromecast is not doing anything fancier than sending an URL to the Chromecast.

Thank you, i didn't know that.

[doiiido]

Hi everyone! Everyone is pointing out at the default receiver app on chromecast, but I've created an (very basic available on the codelab https://www.gstatic.com/eureka/cast_codelabs/src/live_codelab_src.zip) Chromecast receiver app and the delay is still about the same. Do you guys have any notes or wish for me to test specific flags?