[Ffmpeg-devel-irc] ffmpeg.log.20171231

burek burek021 at gmail.com
Mon Jan 1 03:05:01 EET 2018

[00:00:17 CET] <c_14> question 1: why are you rescaling at all?
[00:01:25 CET] <bray90820_> I am actually scanning photos and wanted to make them 1080p while keeping the native aspect ratio
[00:01:38 CET] <BtbN> that doesn't really make sense
[00:01:43 CET] <BtbN> you'd add pointless black bars
[00:02:08 CET] <bray90820_> Keep the aspect ratio of the photo
[00:02:17 CET] <c_14> I assume he has 4:3 images and he's wondering weather to make the width 1080 or the height 1920?
[00:02:28 CET] <BtbN> how do you intend to scale them to a specific resolution, while keeping the aspect ratio?
[00:02:33 CET] <BtbN> The way to do that is to add black bars
[00:03:46 CET] <bray90820_> equivalent of 1080P
[00:03:54 CET] <BtbN> 1080p is 1920x1080
[00:04:00 CET] <c_14> bray90820_: just pick some good DPI setting on your scanner and don't worry about it
[00:04:28 CET] <BtbN> which, for a picture, is quite a lot resolution
[00:04:42 CET] <BtbN> it doesn't really make sense to scale them down. They'd look horrible if you ever printed them again
[00:05:58 CET] <furq> bray90820_: 1080p is 1920 and <=1080 or <=1920 and 1080
[00:06:41 CET] <bray90820_> furq: So if I kept 1920 i should be good?
[00:06:56 CET] <BtbN> why do you want to cripple your image quality?
[00:07:07 CET] <bray90820_> I'm not
[00:07:12 CET] <furq> e.g. 1440x1080 for 4:3, 1920x816 for 21:9
[00:07:16 CET] <BtbN> You're scaling them down massively
[00:07:22 CET] <BtbN> i'd call that cripplin
[00:07:24 CET] <BtbN> +g
[00:07:35 CET] <bray90820_> What resolution would you choose?
[00:07:39 CET] <furq> if this is by any chance for youtube then just make it 1080 high
[00:07:40 CET] <BtbN> the real one
[00:07:43 CET] <furq> that's the only thing they check afaik
[00:07:48 CET] <furq> but yeah for archival just don't scale it
[00:08:04 CET] <bray90820_> That would be 8K then
[00:09:30 CET] <bray90820_> Assuming what I'm viewing a side taken from 32mm film is the same as a negative
[00:13:09 CET] <c_14> depending on the source I might scan at around 4k, depends on what you're going to do with it though. Higher is often better because it offers you more flexibility.
[00:14:01 CET] <c3-Win> I've been told by compositors that when they get 4k (or in some cases 6k) scans of 35mm film they can actually see the individual grains of film.
[00:14:24 CET] <c3-Win> (When viewing the image in 1:1 mode)
[02:21:45 CET] <utack_> Hi. is there a way to see codec specific options for a specified codec?
[02:25:34 CET] <foul_owl> for sharing a video clip on, say, reddit, would you suggest gif or webm?
[02:29:21 CET] <foul_owl> I feel like gifs are easier to share
[02:29:34 CET] <foul_owl> The goal being to upload a clip that can be shared easily
[02:38:35 CET] <utack_> ok figured that out
[02:39:18 CET] <utack_> another question, can i do dual encodes? for example -i source.flac -c:a libopus -b:a 12k -c:a flac opus.flac
[02:50:04 CET] <relaxed> utack_: -i input <encoding options> output1 <encoding options> output2
[02:50:23 CET] <therage3> Opus is impressing me
[02:50:31 CET] <therage3> Even at 64kbps (!) you can only barely discern the artifacts, the music is still very much listenable
[02:50:44 CET] <therage3> Mp3 at 64kbps sounds like garbage
[02:51:39 CET] <therage3> Also, I'm doing some spectrograms of both the lossless source file and 64kbps Opus file. how on earth they managed to keep the frequency content that well in a 64kbps file all the way up to 20kHz is anyone's guess
[02:54:35 CET] <c3-Win> No guessing needed, just read the code! ;-)
[02:57:10 CET] <therage3> that's true, being a free and open-source codec, but it's not easy reading I bet
[02:59:07 CET] <c_14> there's also https://tools.ietf.org/html/rfc6716
[02:59:23 CET] <c_14> It's only 325 pages
[02:59:29 CET] <therage3> (lol)
[04:14:07 CET] <kepstin> yeah, I was just looking at https://people.xiph.org/~jm/opus/opus-1.2/ again a couple days ago - if the 64kbit/s is impressive, try the 32kbit/s sample
[04:14:22 CET] <kepstin> i mean, it's noticably lower quality, but really, that should not be possible in only 32kbit/s :)
[04:14:48 CET] <kepstin> it sounds better than the 64kbit/s mp3.
[04:17:09 CET] <JEEB> mpeg-1 layer 3 is old tho
[04:17:50 CET] <kepstin> true, I suppose a comparison with aac would be more appropriate (but which aac, aac-lc?)
[04:37:29 CET] <Afdal> AAC compares to Vorbis competitively
[04:37:43 CET] <Afdal> but Opus is really the absolutely emperor of audio codec right now
[04:37:56 CET] <Afdal> (lossy codecs)
[04:41:04 CET] <therage3> Agreed
[04:44:17 CET] <c3-Win> he-acc (high-efficiency) would be the one to compare it against. (LC=Low Complexity.)
[10:41:24 CET] <utack_> relaxed thanks. i wanted to encode to codec1 first, then the same file to codec2
[10:41:43 CET] <utack_> i think yours encodes one input to two outputs
[10:43:55 CET] <darsain> how can you set a max fps in encoding? not a specific fps, but max fps, so that anything below will stay unchanged and everything above will get capped
[10:45:04 CET] <darsain> preferably with some method that wont just do a dumb frame dropping when lowering fps and cause the video to stutter
[10:48:17 CET] <utack_> nvm i will just do it in two steps
[11:38:14 CET] <furq> utack_: if you mean you want to encode them one after the other then you'll need to run ffmpeg twice, yeah
[11:38:19 CET] <furq> i'm not sure why you'd want to do that though
[11:38:44 CET] <furq> especially for audio given that the flac and opus encoders are both singlethreaded
[12:01:43 CET] <utack_> furq to compare files in abx, it does not exactly take any "exotic" input files
[14:48:46 CET] <ayum> Hi, I am using h264_nvenc codec, I remember I tested h264_nvenc can reach 600 fps when encoding yuv format video file, but I tested it again at today, the performance is quite strange, the maximum fps is about 450 fps. same yuv video file, same 375.39 driver. what's the problem?
[16:01:07 CET] <Tachyon> ayum: no expert at all, but maybe the frames from yuyv are more difficult to encode?
[16:01:29 CET] <Tachyon> is it possible that it was static image in the past but now it has more moving objects in the scene?
[16:31:07 CET] <ayum> @Tachyon, Hi, my previous test and today test are using same yuv file, as I known so far, YUV file is rawvideo. there is no much overhead on decoding. I also checked is it a disk IO speed problem, but after I copied the yuv file to RAM disk, it's still same 450 fps
[16:31:29 CET] <Tachyon> hm, then I have no clue at all
[16:31:31 CET] <Tachyon> :(
[16:31:37 CET] <Tachyon> but as I said, I'm no expert
[16:32:30 CET] <ayum> @Tachyon, I reinstalled nvidia driver before, perhaps it's the driver problem. I am reinstall everything now. thanks
[20:47:39 CET] <relaxed> utack_: you want to encode to opus and then from opus to flac?
[20:48:11 CET] <therage3> I didn't catch the conversation, but what precisely would be the point of that?
[20:48:47 CET] <therage3> the flac would sound identical to the opus and it would presumably be a bigger file
[20:50:04 CET] <relaxed> I think he wants to test opus encoding with this, https://lacinato.com/cm/software/othersoft/abx , but it doesn't take opus as input
[20:50:48 CET] <relaxed> flac isn't either, so wav
[20:51:14 CET] <therage3> no, I do believe newer versions of the Opus encoder accept FLAC as input
[20:51:16 CET] <therage3> iirc
[20:51:52 CET] <relaxed> I'm talking about abx
[20:52:16 CET] <therage3> aha
[20:55:12 CET] <relaxed> utack_: ffmpeg -i INPUT -c:a libopus -f opus - 2>opusenc.log | ffmpeg -f ogg -i - output.wav
[20:56:08 CET] <kazuma_> should the -i after the pipe refrence somthing?
[20:56:27 CET] <furq> it does
[21:10:32 CET] <aiena> I have a question does anyone know if the ffmpeg VLC uses in ubuntu is different from the ffmpeg as a standalone?
[21:12:42 CET] <relaxed> I would assume ffmpeg and vlc on your system are using the same ffmpeg libs
[21:13:39 CET] <aiena> hmm interesting I think it may be vp9 glitching when seeking with play active
[21:13:58 CET] <aiena> e.g. if vlc is playing the file and you seek to another portion it glitches after a few seconds
[21:14:10 CET] <relaxed> have you tried mpv for video playback?
[21:14:19 CET] <aiena> what is mpv?
[21:14:32 CET] <furq> a video player that isn't vlc and is therefore better than vlc
[21:14:40 CET] <relaxed> it's a video player, mpv.io
[21:14:47 CET] <relaxed> highly recommend it
[21:15:03 CET] <aiena> I would like to try it wonder if it is already in the repos
[21:15:11 CET] <relaxed> yes
[21:15:17 CET] <tomonori__> Hi, I just found why the h264_nvenc performance is bad than my previous test, there is a "surfaces" options in h264_nvenc codec, default value is 32, in this case I can get only 450 fps, but if I change this value to 4, I can get over 600 fps.
[21:15:21 CET] <aiena> ffplay is awesome too but it is restricted
[21:15:32 CET] <tomonori__> anyone know what's this surface options did?
[21:16:19 CET] <therage3> tomonori__: https://ffmpeg.org/pipermail/ffmpeg-user/2016-October/033964.html
[21:16:22 CET] <aiena> relaxed: huh mpv has youtube-dl as a dependency
[21:16:31 CET] <furq> it has youtube-dl integration
[21:16:42 CET] <therage3> oh, that's fancy.
[21:16:45 CET] <therage3> Very nice
[21:16:46 CET] <furq> it's not an actual hard dependency but most distros will mark it as such
[21:16:50 CET] <aiena> ok so it can download with youtube-dl
[21:17:04 CET] <aiena> I have youtuve-dl but non distro managed
[21:18:15 CET] <aiena> furq: I know this is off-topic but does mpv have an option where you can type out the exact seek point you want?
[21:18:20 CET] <aiena> instead of scrobbling
[21:19:29 CET] <furq> if you mean on startup then --start
[21:19:50 CET] <therage3> Also
[21:19:51 CET] <therage3> <furq> a video player that isn't vlc and is therefore better than vlc
[21:19:56 CET] <therage3> ^ LOL
[21:21:59 CET] <aiena> I agree mpv looks good. therage3 honestly ffplay is awesome too
[21:22:15 CET] <therage3> yeah, I noticed it exists, never used it though
[21:22:15 CET] <aiena> only it has difficult GUI interactivity
[21:22:20 CET] <therage3> only ffmpeg and ffprobe so far :p
[21:22:22 CET] <Johnjay_> furq: after reading Bill's Guide from 2000 I think I'm starting to understand anamorphic video
[21:22:50 CET] <tomonori__> @therage3, I have another question about rate control, I see a document said, "if -b:v option is equal to -maxrate option, then ffmpeg is using CBR mode, and if the -maxrate option value greater than -b:v option, then it's VBR, right?"
[21:23:19 CET] <Johnjay_> it's basically cramming extra vertical resolution so you can lower the aspect ratio to work on both letterbox and standard 4:3 screens
[21:24:06 CET] <Johnjay_> therage3: I'm thinking of switching to mpv full time on my windows pc *just* for the resume playlist feature. it's fragile but it works
[21:24:20 CET] <tomonori__> @therage3, but I think it's "if -b:v option + -b:a option value equal to maxrate, it's CBR".
[21:28:53 CET] <furq> maxrate is usually particular to the video stream
[21:28:59 CET] <furq> you might be confusing it with muxrate
[21:29:26 CET] <furq> with that said, at least for x264, that's still not cbr
[21:29:28 CET] <tomonori__> oh, so the maxrate is only for control video stream, right?
[21:29:43 CET] <kepstin> Johnjay_: "anamorphic" is basically "we want to make a widescreen picture, but our recording media is designed for 4:3, guess we'll just squish it when recording then stretch it back for playback
[21:29:49 CET] <furq> x264 has a cbr ratecontrol method that will show up in the encoding settings
[21:30:01 CET] <furq> which pads all nalus to be the same size
[21:30:24 CET] <furq> the settings will say rc=cbr or nal-hrd=cbr or both
[21:30:32 CET] <furq> if those aren't set then it's just rate-limited abr
[21:30:44 CET] <tomonori__> I am using the qsv and nvenc based codec so far, for encoding live stream
[21:30:52 CET] <furq> oh right
[21:31:02 CET] <furq> maybe that statement is true for those, i've never used them
[21:31:04 CET] <tomonori__> I see nvenc actually has cbr and vbr options
[21:31:07 CET] <furq> but it's not true in general
[21:31:24 CET] <furq> that statement being the one you pasted
[21:31:40 CET] <Johnjay_> the main problem i have is both foobar2k and mpv will resume a playlist where you left off
[21:31:43 CET] <Johnjay_> but not in case of a crash
[21:31:49 CET] <Johnjay_> only in case of clean exit with Q
[21:32:28 CET] <Johnjay_> kepstin: that's anamorphic filming, different than anamorphic dvds. i think.
[21:33:04 CET] <kepstin> Johnjay_: nah, exactly the same thing, except that the stretching/squishing is done with digital scalers rather than lenses :)
[21:53:03 CET] <aiena> furq: does mpv use ffmpeg?
[21:56:15 CET] <Johnjay_> well considering it gives errors related to ffmpeg while playing
[21:56:17 CET] <Johnjay_> i assume yes
[22:00:15 CET] <furq> it uses the ffmpeg libs
[22:01:51 CET] <Buster> ! >2K< >4><!
[00:00:00 CET] --- Mon Jan  1 2018

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