1365131 - Youtube videos stop to buffer every couple minutes

Status: REOPENED

(Core :: Audio/Video: Playback, enhancement, P2)

Description

[Katelyn Gadd (:kael)]

For the last month or so (maybe just a couple weeks?) Youtube videos have been stopping to buffer somewhat consistently every 2 minutes or so. Playback halts and it shows the buffering indicator very briefly, then it resumes.

The most likely culprit here seems to be a Firefox change. I'm on Aurora channel.

Comment 1

[Blake Wu [:bwu][:blakewu]]

Thanks for firing this bug. 
I am wondering if that has something to do with network or not. When you see this problem again, could you move your cursor onto the video, press the right button of your mouse and select the "Stats for nerds"? It would be worth checking "Connection Speed" and "Buffer Health" on "Stats for nerds". If possible, please capture it and post it here. 
Thanks.

Comment 2

[Jean-Yves Avenard [:jya]]

YouTube uses MediaSource Extension.

The buffering is entirely controlled by YouTube, Firefox has no control on how much will be buffered ahead of playback.

Download of data is entirely based on the speed of the connection, and whatever logic YouTube decided to implement.

Comment 3

[Jean-Yves Avenard [:jya]]

how are other browsers behaving? (using a desktop)

Comment 4

[Katelyn Gadd (:kael)]

(In reply to Blake Wu [:bwu][:blakewu] from comment #1)
> Thanks for firing this bug. 
> I am wondering if that has something to do with network or not. When you see
> this problem again, could you move your cursor onto the video, press the
> right button of your mouse and select the "Stats for nerds"? It would be
> worth checking "Connection Speed" and "Buffer Health" on "Stats for nerds".
> If possible, please capture it and post it here. 
> Thanks.

(In reply to Jean-Yves Avenard [:jya] from comment #3)
> how are other browsers behaving? (using a desktop)

I will test it out in Edge and Chrome and let you know. If the buffering is entirely under Google's control that rules out Firefox, I guess.

Comment 5

[Katelyn Gadd (:kael)]

Other browsers are fine. I'm going to try to capture the stats when this happens next. Is it possible one of my other open tabs could be interfering with Youtube's ability to fetch video segments? The last two times I watched videos right now, the buffer was in the 25-40s range, which makes it surprising that it could ever need to rebuffer unless it stopped being able to fetch segments. (Could just be Youtube's CDN, I guess?)

Comment 6

[Jean-Yves Avenard [:jya]]

Have you installed any particular extensions?

Please provide copy of about:support data..

If you right click on the video, select stats for nerds. You can have a quick view of what's happening.. like check if it's stalling while you still have data buffered ahead etc..
The last line shows how much data is buffered.

Comment 7

[Katelyn Gadd (:kael)]

Just for an update, this still happens, but isn't consistent. I had two stop-and-rebuffers on a video but when I cleared cache and restarted FF, it played from start to finish just fine.

Stats for nerds doesn't show much other than that it seems like the playback buffer may have instantaneously emptied, causing the rebuffer - but I don't know why that would happen. Under normal circumstances the playback buffer fills to 60+ seconds and doesn't drain until the end of the video.

Pasting about:support

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--

Comment 8

[Katelyn Gadd (:kael)]

Attachment: stats for nerds

Comment 9

[Jean-Yves Avenard [:jya]]

(In reply to K. Gadd (:kael) from comment #7)
> Just for an update, this still happens, but isn't consistent. I had two
> stop-and-rebuffers on a video but when I cleared cache and restarted FF, it
> played from start to finish just fine.


YouTube uses MediaSource extension with XHR request. Those aren't cached. So clearing the cache would have no effect whatsoever.

just luck I guess.

Do you force the resolution when watching a youtube video?

In Auto mode, the youtube player will assess your connection speed and ensure the quality selected allow for continuous playback without interruption.


> 
> Stats for nerds doesn't show much other than that it seems like the playback
> buffer may have instantaneously emptied, causing the rebuffer - but I don't
> know why that would happen. Under normal circumstances the playback buffer
> fills to 60+ seconds and doesn't drain until the end of the video.

buffer being fully cleared typically happens when the youtube player gets a buffer full error. It then clears the entire buffer an restart automatically.

I see nothing in your prefs that could have reduced the size of the allowed buffer (100MB for video, and 15MB for audio)...

Unless you force 4K videos, and machine is too slow to play properly, the buffer should never gets full normally...

The stats for nerds capture (you can just copy/paste the data BTW, much easier than doing a screen capture) shows 35s buffer which is about normal.

Comment 10

[Katelyn Gadd (:kael)]

I've had the buffer get up into the 70+ second range; so if the buffer gets too full it dumps it and restarts? I think that might be happening. Can I identify the size of the buffer in MB somehow? I'm on gigabit fiber, so it's possible it's just filling the buffer faster than it can play it back.

Comment 11

[Jean-Yves Avenard [:jya]]

All of this is controlled by the YouTube JS player.

if you could link to some videos at which it is happening, maybe I can attempt to reproduce it here.

Try this:

create a new integer pref:
media.mediasource.eviction_threshold.video
set the value to 157286400

and:
media.mediasource.eviction_threshold.audio
set the value to 31457280

see if it helps.

Comment 12

[Katelyn Gadd (:kael)]

Attachment: stats after eviction

Thanks for the suggestion, I'll test that.
I tried manually lowering the eviction threshold to test what happens when youtube's buffer is evicted and it doesn't match the problem I'm seeing (though it's quite weird). It's possible eviction is still involved, I suppose.

Is it possible that YT normally won't encounter buffer full errors, and as a result is misbehaving when it gets them (due to my unusual connection and use of FF instead of Chrome)?

Comment 13

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

This smells like buffer bloat to me. You can diagnose this issue with http://www.dslreports.com/speedtest

If the issue occurs, try turning off other devices on the network that may be uploading data. Mobile phones tend to sync photos when they join the network, which saturates upstream and pushes ping times up on problematic networks.

Try pinging 8.8.8.8 to see what your ping times look like when you're having trouble.

Comment 14

[Katelyn Gadd (:kael)]

I'm on gigabit fiber and the speedtest shows no buffer bloat.

Comment 15

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

(In reply to K. Gadd (:kael) from comment #14)
> I'm on gigabit fiber and the speedtest shows no buffer bloat.

Have you tried different machines on the same network or the same machine on different networks? Do you get the same result on Edge?

Does setting media.wmf.vp9.enabled=false make a difference?

Comment 16

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

Feel free to provide the above info and re-open the bug.

Comment 17

[Katelyn Gadd (:kael)]

I think this is probably actually https://bugzilla.mozilla.org/show_bug.cgi?id=1390680 and I didn't notice because it was stopping & restarting playback instead of failing like it does now. (The early failures leading up to complete playback failure in 1390680 do act like rebuffers)

I'll try turning off vp9.

Comment 18

[Katelyn Gadd (:kael)]

Attachment: stats screenshot.png

Sadly this recurs even with wmf.vp9.enabled set to false, though it seems less common. Saw it a few times today, most recently on https://www.youtube.com/watch?v=vrphM1J87rg part way through. I had the stats for nerds overlay open and it seems like the buffer drained suddenly, causing it to pause briefly. I've highlighted the spot where it happened.

Comment 19

[Jean-Yves Avenard [:jya]]

Using Firefox Nightly, Install the media devtools extension.

Then press ctrl-alt-I, then go into the media tab on the right.

Press the start button.

Now plays the video again, and observe the memory use, does it ever reach a particular number before it restarts to 0?

Youre using a standard build right?

Comment 20

[Katelyn Gadd (:kael)]

Regular ol' x64 developer edition. I'll try what you suggested in nightly.

Comment 21

[Katelyn Gadd (:kael)]

Playback failure on https://www.youtube.com/watch?v=pMOrfXMgNU4, which appears to be using the avc1 codec instead of vp9. Is there an about:config value to decode those in software as well?

Comment 22

[Jean-Yves Avenard [:jya]]

yes:
media.hardware-video-decoding.enabled

Comment 23

[Jean-Yves Avenard [:jya]]

if the problem is a sourcebuffer full error, it would show regardless of the video codec used.

Comment 24

[Katelyn Gadd (:kael)]

Part of the issue here is that turning off vp9 seems to have convinced youtube to send me avc for most videos, but some are still vp9.

Where do I find the memory use in media devtools? There are a lot of values here poorly labelled.

Comment 25

[Katelyn Gadd (:kael)]

Also, navigating between youtube videos with media devtools open seems to consistently tab crash.

https://crash-stats.mozilla.com/report/index/e8fd3536-fa1f-4aab-a5e5-029ce0170916
https://crash-stats.mozilla.com/report/index/d0cb5620-ae80-4a66-be80-3631a0170916

Comment 26

[Jean-Yves Avenard [:jya]]

          "Dumping Data for Demuxer": "7f958da8c000",
          "Dumping Audio Track Buffer(audio/webm)": "mLastAudioTime=7,821000",
          "Audio Track Buffer Details": "NumSamples=1390 Size=840650 Evictable=207287 NextGetSampleIndex=391 NextInsertionIndex=1390",
          "Audio Track Buffered": "ranges=[(0,000000, 27,801000)]",
          "Dumping Video Track Buffer(video/webm)": "mLastVideoTime=6,280000",
          "Video Track Buffer Details": "NumSamples=896 Size=2703124 Evictable=178292 NextGetSampleIndex=157 NextInsertionIndex=896",
          "Video Track Buffered": "ranges=[(0,000000, 35,840000)]",


"Size" is how much data the source buffer currently contains
"Evictable"is how much can be ejected.

Size should never go much over 100MiB for video and 15MiB for audio.

I'll lodge a bug for those crashes.

Comment 27

[Katelyn Gadd (:kael)]

OK, it happened once with devtools open, though I wasn't staring at them.

https://www.youtube.com/watch?v=pMOrfXMgNU4 had about 500 seconds buffered after ~10 minutes of playback, and then it briefly paused and the buffer reset to 0. Previously when I looked at it the buffer details showed something like 'numsamples=60000, size=40000000, evictable=38000000' The evictable and size values had been going up the whole time without ever going down, and the buffered range had a start of 0. After the pause/reset the size and evictable numbers had plummeted, and the buffered range starts at 599.04. I don't know if this means that it evicted all the evictable bytes or if it actually just threw the whole buffer away, but it seems like one of those two happened? That or youtube itself gave up and destroyed the media element and created a new one - that would explain the brief pause. (How can I check whether they've done that?)

Comment 28

[Jean-Yves Avenard [:jya]]

was that for audio or video?

Unless the resolution is very low, I doubt 500s of video would only amount for 40MB of data.
You did change your memory threshold though, increasing them greatly. We know it's not that, so please reset them back to their default value.

It is possible you got a decoding error and youtube restarted the media element. That information isn't available via the devtools however (yet) only through logging.



Using MOZ_LOG=MediaFormatReader:5,MediaSource:5 MOZ_LOG_FILE=path_to_file firefox.exe

would help find what exactly happened... It's very verbose ....

What's certain is there's something unique to your configuration, as you can imagine if we had such common issues with youtube, we would have had more reports than just yours.

Comment 29

[Katelyn Gadd (:kael)]

Later in my testing for that clip I got a decoding error and youtube gave up, so I turned off hw decoding. If decoding errors can cause the element to restart that means I may just be getting confused by bug 1390680 and everything else is fine.

The videos are often static images with music attached (soundtracks) so it seems plausible that the size numbers are correct. That was the video track. I'll reset the eviction threshold just to factor that out. YT seems happy to buffer up 500s while paused but it doesn't seem to do the evict/reset thing while paused.

Would it make sense if it were just the result of having a very fast connection? I feel like I'm probably not the only firefox user on gigabit, but it is pretty rare in the US.

Comment 30

[Katelyn Gadd (:kael)]

I haven't seen this in a few months, but I've had hardware decoding disabled that whole time. I'm going to turn hw decoding back on and see if the issue remains resolved.