[Ffmpeg-devel-irc] ffmpeg.log.20190601

[burek]

[00:54:06 CEST] <aruns> Hi there, I have a quick question: when using FFMPEG to reduce a file size of a video, say an MP4, while maintaining enough quality, I was thinking that I could divide the bitrate by 100 and then multiplying it by the desired percentage.
[00:54:22 CEST] <aruns> Is there a target percentage I should aim towards?
[01:12:06 CEST] <kepstin> aruns: you can encode to any size you like by setting a bitrate - whether it "maintains enough quality" depends on a bunch of encoding options (preset in particular, with libx264), and can only really be judged with your eyes
[01:12:40 CEST] <kepstin> aruns: for most use cases I recommend using the -crf option with libx264 to set the desired quality level, and then the encoder will make the video as small as it can while maintaining that.
[01:18:42 CEST] <aruns_> Ah OK, thanks kepstin
[01:19:10 CEST] <aruns_> kepstin: So something like the following should be OK: ffmpeg -i input.mp4 -c:v libx264 -crf 28 -preset slow -c:a copy output.mp4
[01:21:01 CEST] <kepstin> Yeah, but -crf 28 looks pretty bad. Try a few values on short clips to see what you like.
[01:21:37 CEST] <kepstin> Lower numbers are higher quality, default is 23
[01:24:11 CEST] <aruns_> The original MP4 is about 2.2G
[01:24:34 CEST] <aruns_> I am trying to figure out what the ideal size should be, as I want to transfer it to the cloud NAS I have configured at home.
[01:24:54 CEST] <aruns_> It's a full movie, so may take a while to convert.
[01:25:41 CEST] <aruns_> Thanks, I have the command in place now :)
[01:27:08 CEST] <BtbN> The ideal size is however bad you're okay with it looking
[01:34:30 CEST] <gentwo> Hi, i am trying to playback a file, ffplay error shows "Could not initialize SDL - No available video device (Did you set the DISPLAY variable?)". gone through couple of options from google but none of them seems to be working . i am on gentoo and all use flags are set porperly.
[01:41:27 CEST] <gentwo> username234 echo $DISPLAY shows 0:0
[02:47:16 CEST] <gentwo> problem resolved by rebuilding libsdl2 with alsa support
[22:20:00 CEST] <Erasmus> I am on macos mojave have ffmpeg installed with homebrew. I cannot convert a flac file to mp3.
[22:20:11 CEST] <Erasmus> I get Illegal instruction: 4.
[22:20:19 CEST] <Erasmus> don't know what else to try.
[22:20:21 CEST] <Erasmus> help.
[22:20:32 CEST] <JEEB> full command line and terminal log with -v verbose at the very least in a pastebin
[22:20:35 CEST] <JEEB> then link the pastebin or so here
[22:20:43 CEST] <Erasmus> ok
[22:21:51 CEST] <Erasmus> https://paste.lowtech.io/?345bb0df37b03f5c#/JQroFjR+gln3vt62y9wM2NjQaDpTp4zQvk8wPgiI8I=
[22:22:22 CEST] <Erasmus> https://paste.lowtech.io/?9ae3e3c87f24047a#kYIUkLR4+X5tu0j0chFBB0gtcUiyxTAYQ7x51YGuEG4=
[22:23:15 CEST] <JEEB> you built that yourself through homebrew right?
[22:23:32 CEST] <JEEB> can you install it with disable-stripping and then check out with lldb where it crashes exactly?
[22:23:46 CEST] <JEEB> it seems to get far enough where it kind of starts up, but then something borks
[22:23:50 CEST] <Erasmus> yes
[22:24:03 CEST] <JEEB> so basically --disable-stripping in addition to the other flags
[22:24:07 CEST] <JEEB> that should keep debug symbols
[22:24:08 CEST] <Erasmus> so unlink and remove it and then what?
[22:24:28 CEST] <JEEB> no I mean, just rebuild with the debug symbols included (--disable-stripping)
[22:24:37 CEST] <JEEB> then https://lldb.llvm.org/lldb-gdb.html
[22:24:50 CEST] <JEEB> then you'll have to poke lldb to execute your command
[22:24:56 CEST] <JEEB> and see where it crashes and post the backtrace
[22:25:06 CEST] <Erasmus> i don't understand
[22:25:43 CEST] <JEEB> to give you any sort of help since I have never seen such an error on macs so far, we'll need a backtrace
[22:26:03 CEST] <Erasmus> I used homebrew to install it
[22:26:16 CEST] <JEEB> to get a readable backtrace you need to give homebrew's FFmpeg the option --disable-stripping
[22:26:18 CEST] <Erasmus> brew install ffmpeg --HEAD
[22:26:21 CEST] <JEEB> in addition to the stuff you already have there
[22:26:36 CEST] <Erasmus> brew install ffmpeg --HEAD --disable-stripping
[22:26:45 CEST] <Erasmus> that?
[22:26:55 CEST] <JEEB> no, you'll have to check out homebrew how to add/remove configuration options
[22:27:18 CEST] <JEEB> since most likely it will not read additional options from the brew command line like that :P
[22:28:32 CEST] <JEEB> sorry, I don't use homebrew myself so I can't tell you how to get it done easily. alternatively, we can try building separately from homebrew if you want :P
[22:28:50 CEST] <Erasmus> https://trac.ffmpeg.org/wiki/CompilationGuide/macOS
[22:28:53 CEST] <Erasmus> that is what I did.
[22:30:04 CEST] <JEEB> that doesn't help you or me. that's just stuff written by someone at some point
[22:30:10 CEST] <JEEB> it's not like the wiki is write protected
[22:30:23 CEST] <JEEB> and I just don't know homebrew specifically so I will not be of use with homebrew
[22:30:59 CEST] <JEEB> in short I have a heavy hunch that your problem is not with FFmpeg itself but something built into it, but to prove that and figure out where the issue lies, we'd have to get a backtrace
[22:31:24 CEST] <JEEB> or the configuration specified by that homebrew formula
[22:31:28 CEST] <Erasmus> that is what you get when you search homebrew in https://trac.ffmpeg.org/search?q=homebrew
[22:32:05 CEST] <JEEB> yes? I mean, that still doesn't help you or me
[22:32:14 CEST] <JEEB> I don't know about homebrew and you don't seem to either
[22:32:34 CEST] <JEEB> I just know what the next steps would be to seek out answers to your problems :P
[22:32:39 CEST] <JEEB> in the context of FFmpeg itself
[22:33:31 CEST] <JEEB> of course you can test creating a backtrace with the build you currently have
[22:33:41 CEST] <JEEB> but it probably won't have too much use :P
[22:33:53 CEST] <JEEB> see the lldb page I linked
[22:34:08 CEST] <JEEB> ah, there is also a tutorial for lldb https://lldb.llvm.org/use/tutorial.html
[22:34:20 CEST] <JEEB> basically you need to launch ffmpeg under lldb :P
[22:35:11 CEST] <JEEB> (also jesus that tutorial is not really a tutorial - the only quickly useful part I can see is the process launching)
[22:35:18 CEST] <JEEB> which thankfully is in the beginning
[22:36:20 CEST] <JEEB> ok, so backtrace is "bt" in lldb as well :P
[22:37:02 CEST] <JEEB> without debug symbols in your FFmpeg build it's not gonna give much but if you really can't figure out how to make homebrew add an option to the FFmpeg configure, then it might be worth a shot to try it with your current one
[00:00:00 CEST] --- Sun Jun  2 2019