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  1. Member
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    [apologies if this is asked before -- perhaps I don't know what to search for, but I've come up empty]

    I have a few *.mkv files holding H.265/AAC. When I view in vlc I can't easily skip around because the index seems to restrict seeking to very large movements only (intervals of about 50 seconds).

    Is it possible to regenerate just the indexing without transcoding the entire h.265 stream? If so, what's the recommended method? I'm comfortable with the linux command line, and megui, etc.

    Thanks for any tips!

    --------

    In case it helps, codec info from vlc:

    Codec: MPEG-H Part2/HEVC (H.265) (hevc)
    Decoded format: Planar 4:2:0 YUV

    Codec: MPEG AAC Audio (mp4a)
    Channels: 3F2R/LFE
    Sample rate: 48000 Hz
    AAC extension: SBR
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  2. Turn off Fast Seek in VLC. You can then seek to any frame -- but it may take a while with very long GOPs.

    In other words, there's probably nothing wrong with the index in your files. It's just that they were encoded with very long GOPs and VLC is set up to seek to the nearest keyframe (fast seek) not the requested frame (which can be very slow with long GOPs).
    Last edited by jagabo; 10th Oct 2016 at 08:53.
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  3. Member
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    Originally Posted by jagabo View Post
    Turn off Fast Seek in VLC.
    Thank you! I checked and fast seek is already off in VLC. Maybe a bug in VLC? I tried to find a PPA to upgrade to 2.2.4 but the only one I found did not work. But 16.10 will be out in a few days so I can check again then...

    In other words, there's probably nothing wrong with the index in your files. It's just that they were encoded with very long GOPs and VLC is set up to seek to the nearest keyframe (fast seek) not the requested frame (which can be very slow with long GOPs).
    Yeah what I was hoping for was a way to insert some keyframes into the GOPs without recompressing the whole stream, but I can see how that might be impossible.
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  4. You have to reencode if you want more frequent key frames.

    MediaInfo might show you the keyframe interval used to make your video. x265 stores the keyframe interval (along with all the other settings) in the metadata (the default is 250 frames). Other h.265 encoders may not.
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    Is that "keyint="? Yeah, says 1200, which comes to about 50 seconds at 23.976fps, which is exactly what I'm seeing. And I guess VLC just has a bug where it doesn't or can't slow seek in these MKVs? Or is there something else in the settings that might be causing that?:

    Writing library :
    x265 1.7+509-f4c267f28487:[Windows][GCC 4.8.2][64 bit] 8bit

    Encoding settings :
    wpp / ctu=64 / min-cu-size=8 / max-tu-size=32 / tu-intra-depth=1 / tu-inter-depth=1 / me=3 / subme=3 / merange=57 / no-rect / no-amp / max-merge=2 / temporal-mvp / no-early-skip / rdpenalty=0 / no-tskip / no-tskip-fast / strong-intra-smoothing / no-lossless / no-cu-lossless / no-constrained-intra / no-fast-intra / open-gop / no-temporal-layers / interlace=0 / keyint=1200 / min-keyint=23 / scenecut=40 / rc-lookahead=250 / lookahead-slices=0 / bframes=8 / bframe-bias=0 / b-adapt=2 / ref=3 / limit-refs=0 / weightp / weightb / aq-mode=1 / qg-size=32 / aq-strength=1.00 / cbqpoffs=0 / crqpoffs=0 / rd=3 / psy-rd=0.30 / rdoq-level=0 / psy-rdoq=0.00 / signhide / no-deblock / sao / sao-non-deblock / b-pyramid / cutree / rc=crf / crf=25.0 / qcomp=0.60 / qpmin=0 / qpmax=51 / qpstep=4 / ipratio=1.40 / pbratio=1.30
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  6. Yes, that's the keyframe interval. You might try using a different output module. Or turning off/on GPU decoding.
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    Thanks -- no luck, though...
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  8. Are there no scene changes in the movie? Always 50 seconds between? Since scenecut detection was activated there should normally be additional seeking points at each scene change. I don't know what muxer you used. You could try to extract the video using mkvextract and then mux again using mkvmerge (not directly remux from mkv to mkv).

    (VLC 2.X has known problems with open-gop in mp4, but not in mkv AFAIK. But maybe you want to try VLC 3.X nightly anyways.)
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    Originally Posted by sneaker View Post
    Are there no scene changes in the movie? Always 50 seconds between? Since scenecut detection was activated there should normally be additional seeking points at each scene change.
    Yeah, there are some spots where there were <50s keyframes, but they aren't common. Most of the jumps are at or near 50s.

    I don't know what muxer you used. You could try to extract the video using mkvextract and then mux again using mkvmerge (not directly remux from mkv to mkv).
    Thanks for the tip -- VLC says metadata is: _STATISTICS_WRITING_APP : mkvmerge v8.2.0 ('World of Adventure') 64bit
    (I didn't encode the files.)

    ...still worth a remux?

    (VLC 2.X has known problems with open-gop in mp4, but not in mkv AFAIK. But maybe you want to try VLC 3.X nightly anyways.)
    I'll keep that in mind, thanks very much.
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  10. Originally Posted by chconnor View Post
    VLC says metadata is: _STATISTICS_WRITING_APP : mkvmerge v8.2.0 ('World of Adventure') 64bit
    (I didn't encode the files.)

    ...still worth a remux?
    Probably not. Of course doing this is not difficult. Just costs a few minutes of your time.

    The other way you might be able to improve seeking time is to improve decoding performance. VLC 32 bit HEVC decoder is very slow. You might want to try Lentoid HEVC decoder. It's a DirectShowDecoder so you need to use it in a DirectShow player like MPC-BE or MPC-HC. (Can't tell you from the top of my head which of those still works with Windows XP SP2. I believe MPC-HC's included filters might require SP3.)

    For future encodes just remember to choose a lower keyint...
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