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PostPosted: Sun May 01, 2016 12:27 pm 
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Joined: Fri May 21, 2004 11:55 pm
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Location: Silicon Valley, CA
Now that I'm transcoding Blu-Ray discs for my LH box, I'm running into an issue where my 16MB buffer for the internal player just isn't enough. I'm running a networked disk so the buffer size is currently 16MB and I'd like to push that up to 32 or even 64MB. I can't find any messages about changing this buffer size, so I'm wondering if any experts around here (I'm looking at you brfransen) have changed this or know how its controlled...

Joe B.

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PostPosted: Sun May 01, 2016 8:26 pm 
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Even more mysterious...

I find that SOME of my Blu-Ray rips play with 32M buffers, and others play with 16M buffers. All were ripped in the same way, with the same software (DVDFab9 for Mac).

How does the Myth internal player choose its buffer size? I am totally mystified.

My least favorite thing about Myth is that it hides so much of its machinations and it just seems impossible to find out tech details like this. When it works, it works great. But when it doesn't, you're pretty much stuck.

-- Joe B.

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PostPosted: Mon May 02, 2016 8:08 pm 
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Joined: Tue Aug 15, 2006 11:14 am
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Location: Orlando FL
Off the cuff educated guess
Not all blu-ray video files are created equal. Some are high bitrate and others are low bitrate. It all depends on how many bonus features they wanted to cram on to the disc.
How are you seeing the buffer size?

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PostPosted: Tue May 03, 2016 6:28 am 
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Matt, the buffer size can be found in the menu Playback > Playback Data.

Joe, I am not sure how that buffer is calculated and set but it does vary for me as well from 4MB to 32MB. It does seem that it is related to bit rate but there must be other factors as well because many of my recordings that are similar in bit rate end up with different buffer sizes. However, I don't recall ever seeing the available buffer below 99%. What are you seeing for available?


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PostPosted: Sat May 14, 2016 3:16 am 
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I've discovered that the "internal" player gives local video files a 4M buffer, networked files 16M, and "Matryoshka" (MKV) format files 32M. There does not seem to be any way to override or modify these defaults.

My video files are coming from a networked server, so they default to 16M buffer size. The 16M buffer does not provide enough buffering for a blu-ray converted to h.264 format in the MP4 format. The buffer starves when the video becomes busy and causes such gaps and jumping that it really isn't watchable. I can copy the BD file in MPEG2 form and it plays perfectly, but has an enormous size (typically 40-50GB).

I've had most success converting my BDs to Matryoshka format. The internal player assigns 32M buffering and the file plays perfectly. For some unexplained reason, the MKV container file winds up larger than the MP4 container, even with the same CRF encoding scheme and the same quality factor. But it plays perfectly in MKV format and will not play in MP4, so the choice is simple.

Joe

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PostPosted: Sat May 14, 2016 10:59 am 
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Are you sure it is not just a network IO issue? Have you tried copying the problem files local and playing them just to test? If there is still a problem it could be the compressing is too much for your CPU or video card.


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PostPosted: Sat May 14, 2016 5:25 pm 
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I'm using a pretty hefty Intel i5 dual-core and VAAPI for the playback, thanks to your expert help! I retired the little Celeron and replaced it with this i5 "cube" computer. It's a small box with only room for a PCIe SSD drive and some laptop memory.

The encodings are all h.264 using various container formats, chiefly MP4 and MKV. Recordings encoded with MP4 get assigned a 16M buffer, those done with MKV get a 32M buffer. The difference is that the 16M recordings drop quickly to 0% buffer and stall while the 32M ones never do. Movies are all high-budget, ultimate-quality HD-DVDs such as StarWars, Alien Anthology, and Lord of the Rings. Lots of eye-candy, lots of playback processing. VAAPI does an amazing job. The CPU loading never gets to 10%. It coasts by with one or two processors turning in 4-8% and the rest at 2%.

Network I/O is always problematic, but I've done the best I could here. The myth box is sitting on the same switch as my Drobo5N network file storage box. The Drobo has 5 drives, all 7200 RPM and NFS-rated, and an SSD for extra read caching. I've used both CIFS and NFS to mount the shares, to see if that makes a difference (it does not). The sustained read rate over the network is better than 80 Mbytes/sec, which is close enough to the theoretical max at 1 Gbps not to matter. It doesn't speak to the latency, but I hope the SSD is helping there. I used Netgear "Pro" switches so I could add some VLANs in the future if I want, but they are working as just simple switches now.

While it make be true that the system could easily handle a local h.264 recording, even though it would only get a 4M buffer and not the 16M that "normal" (not MKV) network shares get. But that would be kind of a pointless experiment as I'm not going back to internal drives for my myth box. There are just too many benefits to the network drive to go back.

-- Joe

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