[Ffmpeg-devel-irc] ffmpeg.log.20140401

burek burek021 at gmail.com
Wed Apr 2 02:05:01 CEST 2014

[01:49] <voip> hello guys !
[01:49] <voip> please help me, where is mistake ?
[01:49] <voip> http://pastebin.com/NfXfnSx9
[01:50] <voip> its works on FFmpeg version 0.6.5
[02:10] <voip> llogan, can you help me pls ?
[03:01] <relevart> Hello, I'm trying to stream a 4k video with 200Mb/s+ bitrate. Turns out my laptop isn't fast enough. When I run it on my desktop(better CPU), I noticed a significant drop on decoding time - but an increase in scaling. I can't figure out why, please help! thanks
[03:04] <klaxa> 200 Mb/s is quite a lot
[03:04] <relevart> yeah I know
[03:04] <klaxa> also can you explain what you mean with scaling?
[03:05] <relevart> thanks I used sws_scale in FFmpeg library to scale the decoded frame into RGBA
[03:05] <relevart> and then update it with SFML texture to display
[03:06] <klaxa> never really used either
[03:07] <relevart> T.T it's hard to find related topic online
[03:07] <relevart> but thanks anyway
[08:08] <voix> im confused, first I read that coax can only deliver compressed 1080p, but then this product says it delivers full 1080p over coax from HDMI inputs http://www.provideoinstruments.com/pvi-hd-rf-modulators.html
[09:59] <luc4> Hello! Anyone who knows whether it is possible to mux an h264 stream without having to provide a h264 encoder?
[10:11] <brontosaurusrex> luc4, sure, what you need is a "muxer"
[10:12] <luc4> brontosaurusrex: in my code, which is working at the moment, I use avcodec_find_encoder to find codec info. Then I avformat_new_stream passing the codec info. How can I get the codec info without having the encoder? That is my problem.
[10:13] <brontosaurusrex> luc4, that would be over my head
[10:14] <luc4> brontosaurusrex: I'll keep trying then. Thanks anyway.
[13:34] <dannyzb> question : HTTP PSEUDO , RTMP or HLS ?
[13:34] <dannyzb> which one is better for the user and which one takes me less bandwidth
[14:14] <deni> i have a webm video that's 1366x713 resolution and i want to downscale it to 320x240. the command i'm using is:ffmpeg -i screencast.webm -s 320x240 -qscale 0 output.webm
[14:15] <deni> but the output video is so blurry...the text can't event be seen
[14:16] <relaxed> deni: look at `ffmpeg -h encoder=libvpx | less`
[14:17] <relaxed> deni: and use -crf instead of -qscale
[14:18] <deni> relaxed: tnx
[14:26] <deni> relaxed: i used -crf 63. the problem now is that random blurryness shows up here and there
[14:26] <deni> relaxed: i'm trying to make a screencast (of a terminal session) more readable
[14:29] <Jack64> crf 63 is very high
[14:29] <Jack64> crf 0 = lossless
[14:29] <Mavrik> default crf is about 25 not 60 :))
[14:29] <Jack64> crf 18 = widely accepted as visually lossless
[14:29] <iive> high quant -> low quality
[14:29] <deni> Jack64: Mavrik let me try 18 then. tnx
[14:29] <Mavrik> Jack64, is the scale the same for H.264 and libvpx
[14:30] <iive> or rather: high quant -> high loss
[14:30] <Jack64> not sure, I only work with H.264 -.-
[14:31] <Jack64> deni: make sure you have enough space to store the result files, they will be bigger than the ones generated using crf 63
[14:31] <deni> Jack64: it's a small video so no issues there. the text sill ends up being way to small
[14:32] <deni> :(
[14:32] <Jack64> well, you're reducing the video but you're not keeping the aspect ratio
[14:32] <Jack64> 1366x713 is not a common resolution
[14:33] <Jack64> and its ratio is not the same as 320x240
[14:34] <Jack64> so if you don't want stretched heads and whatnot, the real resolution you may want is something like 320x167
[14:34] <Jack64> try that
[14:34] <Jack64> and since you're going with such a low res, try crf 0
[14:34] <iive> avoid odd resolutions
[14:35] <JEEB> he is downscaling text, and I'm pretty damn sure that's not a good idea, esp. with 4:2:0
[14:35] <iive> better use multiples of 4,8 or 16
[14:35] <JEEB> > downscaling text > saying it isn't readable
[14:35] <JEEB> > all my little asdf
[14:35] <deni> Jack64: i used Kazaam for getting a screencast of the terminal window...not sure why it has such an odd resolution
[14:36] <Jack64> well that may be due to bad Kazaam configurations or odd monitor resolution
[14:36] <JEEB> if possible, rather crop than scale down the clip
[14:36] <JEEB> because unless your font size is absolutely humongous, the scaling is not going to be doing good things to readability
[14:37] <deni> Jack64: iive JEEB actually the clip is perfect as is when watched in full screen....the issue is when i emmbed it into a html video tag...then it becomes to small and not readable
[14:37] <deni> i mean i'm not sure i'm even doing the right thing here.
[14:37] <deni> JEEB: the font was really big when i took the screencast
[14:39] <iive> you are decreasing resolution about 4x3 times, it is normal that details are lost.
[14:39] <luc4> Hello! When I build ffmpeg I get after configure "debug symbols    yes". Does this mean I'm building in debug mode?
[14:40] <deni> iive: so the solution would be to record the screencast in a lower resolution so when i put into the video tag it doesn't need to to any resizing?
[14:40] <iive> i though that you are already doing that...
[14:40] <iive> scaling before encoding...
[14:41] <iive> scaling down throws away data, then you do encoding that throws away more data...
[14:43] <deni> iive: what i've done is record the screencast with kazaam which recoreded a video at 1366x713 (no idea why that weird resolution). i've put into the video tag that's 770x400 because that's the box i have on the website. i saw the text was tiny...and figured maybe if i lowered the resolution then the html would not need to do resizing and the text would be more readable
[14:43] <deni> that's the reasoning any way
[14:43] <deni> which may well be stupid/crazy/wrong
[14:43] <deni> i have no experience with video what so ever
[14:44] <iive> oh, scaling is what the web player have been doing...
[14:44] <iive> originally
[14:46] <iive> it is simple, every computer display have resolution of WxH pixels. some are 640x480, 1024x768, 1280x720, 1920x1080.
[14:47] <deni> yeah mine has 1366x768. and the 713 part might be bacause i was screencasting only a window...not the entire screen
[14:47] <iive> if you want to show 1920x1080 on 1280x720 display, you have to throw away some pixels. to smooth the image, pixels are averaged, so this causes blur.
[14:49] <iive> if you want to show 640x480 image on 1920x1080, you can double and quadrupel every pixel, but to make it less obvious, the new pixels are averaged over the existing ones. So the new image looks more blurry.
[14:50] <iive> now... i don't know what the image is...
[14:51] <iive> but let's say that the program have recorded the whole desktop (1920x1080) but you want only the portion with the terminal. if the terminal is just 640x480 window, then you can cut the rest of the image that you don't want.
[14:51] <deni> iive: the video is just me typing away in the shell...showing of a cli tool
[14:51] <iive> this process is called crop or cropping.
[14:54] <iive> what i'm saying... if you had a terminal window that is too big, it might contain scrollback and black areas that are not interested.
[14:54] <iive> you can cut them out, or you could redo the recording with smaller windows terminal.
[14:55] <deni> iive: i used the terminal window maximized
[14:55] <deni> iive: so better to have a smaller window and then just crop it
[14:55] <deni> iive: but then i would need to now the exact pixels what to crop right?
[14:56] <iive> it is possible that the program captures only the window.
[14:56] <deni> iive: duh..or that yes
[14:57] <iive> there are laptops with 1366/768 resolution.
[14:59] <iive> for crop you basically need 4 numbers. the width and height of the window you want to keep, and the x,y coordinates where that window starts.
[15:00] <iive> 0,0 is usually the upper left corner.
[15:01] <deni> iive: the screencasting tool can already take a screencast of only that window so there should be no need for croping
[15:02] <iive> great.
[15:29] <deni> iive: tnx for your help iive
[16:06] <damir__> hello
[16:15] <iive> damir__: hallo, if you have question, ask right away. if somebody knows the answer, it might answer when they look at the irc window..
[16:15] <iive> gah...
[17:03] <t4nk023> Hey guys, I'm building an android application, and I need to use some ffmpeg command. I've got a source video and I need to edit it: 1) Cut only the last 7 seconds. 2) Add a watermark(logo) on the top left side of the video.(00:00-00:07) 3) Add a video inside the source video on the bottom right side of the video.(00:00-00:07)  4) Add another video to the edited video from steps 1-3 (00:07-00:10)\  Can I do it in one ffmpeg command li
[17:05] <klaxa> your message got cut off at: "Can I do it in one ffmpeg command li"
[17:07] <t4nk023> Yes sorry,"Can I do it in one ffmpeg command line? What do I need to consider when I'm editing a video for a cellphone(quality,sizing..)?  Thank a lot!"
[19:04] <TekniQue> How can I detect if the source video being decoded by libavformat is interlaced or not?
[19:04] <TekniQue> I can't see any field to indicate that in AVCodecContext or AVFormatContext
[19:05] <TekniQue> am I blind or is there some other trick to it?
[19:08] <JEEB> I think there's a per-AVFrame field?
[19:08] <JEEB> also lavf doesn't decode
[20:29] <llogan> voip: did you figure out whatever problem you had? I was AFK.
[20:55] <voip> Hello guys
[20:57] <llogan> greetings and salutations
[21:03] <TGMCians> Hi everyone !
[21:03] <TGMCians> I am looking for official library of ffmpeg for android
[21:03] <TGMCians> Any link please, I did not find on their site
[21:10] <voip> I am tryng to convert pal rtmp stream to ac3 ntsc http://pastebin.com/bZWrkCAc
[21:10] <voip> as result i have very high cpu usage
[21:11] <voip> can you chek pls, everutink is ok with ffmpeg commands? Or i can youse more optimal settings ?
[21:39] <voip> http://pastebin.com/2rDYULaD
[21:40] <quidnunc> Anyone know if there is a way to subscribe only to control data in an RTMP stream? That is, request not to have video/audio transmitted?
[00:00] --- Wed Apr  2 2014

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