x264 - bitrate always spikes high during beginning of video

[palaceplace]

edit: Spikes also happen randomly and climb as high as 51mbps, there are many spikes


[Attachment 50366 - Click to enlarge]

Im trying to convert some videos into bluray compliant streams and I have seen spikes as high as 180mbps during the first 3 or so seconds of my video. This freezes up my bluray player and stutters in the beginning and its not ideal. I managed to semi-solve this by applying a lighter black blank color during the beginning of the movie because it goes from complete black, to a cut to a light black solid and then it fades to the intro logo, now it spikes at 47mbps instead, but still high.

My guess is that it spikes because there is a sudden change in solid color shade in the beginning because after I fixed that shade to be one shade then gradually fade into the logo, the 100mbps+ spike dissapears. Here are my settings, what am I doing wrong? (1080p 24fps footage progressive and using an x264 frontend encoder for in adobe premiere):


[Attachment 50365 - Click to enlarge]

[sophisticles]

That's the way CRF encoding works, which is why I consider it a half baked encoding option, use 2 pass if you don't want the encoder to vary the bit rate wildly.

[jagabo]

Or just cap the peaks using bluray-compat, vbv-maxrate, and vbv-bufsize. Beware that Bitrate Viewer's report does not correspond to what's really needed for dvd or bd compatibility.

http://www.x264bluray.com/home/1080i

[pandy]

you need to specify max bitrate and sane buffer size - something like: "level=4.0:qpmin=8:vbv_maxrate=16000:vbv_bufsize=1 2000"

[KarMa]

That's the way CRF encoding works, which is why I consider it a half baked encoding option, use 2 pass if you don't want the encoder to vary the bit rate wildly.

Or maybe just use Bluray compliant settings -_-

--bluray-compat --vbv-maxrate 40000 --vbv-bufsize 30000 --level 4.1 --keyint 24 --open-gop --slices 4

[poisondeathray]

That's the way CRF encoding works, which is why I consider it a half baked encoding option, use 2 pass if you don't want the encoder to vary the bit rate wildly.

He's not using CRF...




His screenshot shows BD compliant settings , ABR 33000, maxrate 34000, buffer 30000 . Which front end is it ? Maybe it's not being passed correctly

You'd have to run it through a buffer analyzer to see if the spikes were violating VBV restrictions and contributing to the playback issues

Bitrate viewer is useless for this because it doesn't take into account the current buffer level at time "X"

[KarMa]

I'd suggest OP switches to voukoder encoder ( a free FFMPEG addon for Adobe PP that supports x264), and then make sure your GOPs are 24 frames as that GUI image you posted does not seem to support keyframe settings.

https://forum.videohelp.com/threads/385325-New-free-x264-plugin-for-premiere

[poisondeathray]

then make sure your GOPs are 24 frames as that GUI image you posted does not seem to support keyframe settings.

Actually it does, in the screenshot - that max GOP size setting is unchecked . That could be the problem

[palaceplace]

I was thinking about decreasing my buffer size but using the official x264 bluray compat guides they all put 30000 for it, and 40000 as max bitrate, but using that option spikes it even higher around the 50's

I'd suggest OP switches to voukoder encoder ( a free FFMPEG addon for Adobe PP that supports x264), and then make sure your GOPs are 24 frames as that GUI image you posted does not seem to support keyframe settings.

https://forum.videohelp.com/threads/385325-New-free-x264-plugin-for-premiere

actually this IS Voukoder, some settings arent word for word exactly like x264 so I got as close as I could form my other x264 presets non-Voukoder interface, maybe I did something wrong. Because some settings arent the same term, I'm not sure how keyint comes into play in this interface, I was guessing keyint had something to do with the GOP settings but unsure I hadnt touched it

Actually it does, in the screenshot - that max GOP size setting is unchecked . That could be the problem

I was thinking this could be the issue too, Ive only been really used to the term "keyint" from other h264 encoders, but im not sure how keyint translates to MAX GOP, should max gop be set and be 24? I'm not really sure how that works, should I checkbox it at 250? (x264 says 250 is reccomended but unsure about bluray compat). Honestly i think it might be the whole keyint thing, Voukoder though uses different terminology and commandline options. I might try regular x264 first, maybe it could be Voukoder as well

[jagabo]

GOP size _is_ keyint (max keyframe interval). The max for Blu-ray is 1 second of video. That means 24 for 24 fps, 60 for 60 fps, etc. The default in x264 is 250.