[Ffmpeg-devel-irc] ffmpeg.log.20180623

burek burek021 at gmail.com
Sun Jun 24 03:05:01 EEST 2018

[01:31:37 CEST] <Trel> I'm having an issue with mp3 tagging, command I'm using is this: https://pastebin.com/s5q5WNyR  I get the art, but no tags.
[01:36:07 CEST] <Trel> (I did fix title->track since I did that paste, it makes no difference)
[01:39:05 CEST] <Trel> *try, not fix
[01:47:04 CEST] <Trel> Nevermind, sorry to have been a pain, I needed -id3v2_version 3
[02:05:17 CEST] <TheAMM> Does ffprobe (ffmpeg) differentiate between MPEG-TS and M2TS?
[02:05:33 CEST] <furq> no
[04:31:20 CEST] <ariyasu_> https://i.imgur.com/hCEZiiQ.png
[04:31:42 CEST] <ariyasu_> is there anyway to get subtitles to display at specific locations in .srt or .ass like in the .vtt ?
[04:32:05 CEST] <ariyasu_> im just doing "ffmpeg in.vtt out.srt" or "ffmpeg in.vtt out.ass" at the moment
[04:32:18 CEST] <ariyasu_> but subs loose there placement
[07:27:57 CEST] <teratorn> any techniques for profiling a filter-graph execution ?
[09:22:41 CEST] <Mavrik> I've just used standard CPU profilers and ffmpeg builds with debug symbols
[09:22:44 CEST] <Mavrik> If that's what you mean
[09:30:56 CEST] <kepstin> if you're at a higher level, and are just trying to figure out "which filter is slow?", I don't really know any way to do that without just profiling the code, yeah
[09:31:40 CEST] <Mavrik> But most filters aren't really that slow - the only one that rivals encoder CPU use is yadif
[10:45:28 CEST] <limbo_> What encoding settings should I use to make a streamable vp8 or vp9 .webm? i.e. so it can be played without being fully downloaded/encoded.
[10:47:03 CEST] <Mavrik> Just make sure your GOP is reasonable and it's fine
[10:47:10 CEST] <Mavrik> WebM is structured in a way that's streamable
[10:47:30 CEST] <Mavrik> mkclean can do some additional help apparently
[10:53:10 CEST] <limbo_> oh. Neat. Also looks like ffmpeg can use - as an input, meaning stdin.
[11:03:17 CEST] <JEEB> yes, that is more or less standard in multimedia tools. you might need to specify the i/o container in those cases with -f , though
[17:50:38 CEST] <fnstudio> hi all, tl;dr: how bad is two compress a file twice, quality-wise? more details follow
[17:51:02 CEST] <fnstudio> i have a large video file that i need to edit
[17:51:15 CEST] <fnstudio> the editing process is slowed down by the file size
[17:51:40 CEST] <fnstudio> the final (edited) video doesn't have to be very hi quality
[17:52:22 CEST] <fnstudio> so i was thinking of compressing it a first time -> doing the editing -> exporting it (and hence compressing it a second time)
[17:53:01 CEST] <fnstudio> but i'm afraid that combining two compressions might heavily affect the quality
[17:53:09 CEST] <fnstudio> am i making sense?
[17:53:43 CEST] <fnstudio> oh sorry, at the very top: s/two compress/to compress/
[20:48:19 CEST] <benlieb> what does a 'program' mean in a video container?
[20:48:37 CEST] <JEEB> a separate stream within a single mux
[20:48:45 CEST] <JEEB> most often seen in mpeg-ts
[20:49:20 CEST] <benlieb> hi jeeb
[20:49:30 CEST] <benlieb> sorry what is a mux exactly?
[20:49:35 CEST] <benlieb> I should know this probably.
[20:50:03 CEST] <benlieb> arent all streams "separate"
[20:50:05 CEST] <JEEB> single multiplex
[20:50:21 CEST] <JEEB> well yes, but a program is a group of streams
[20:50:34 CEST] <JEEB> like, in mpeg-ts it's usually completely separate channels
[20:50:42 CEST] <JEEB> or services
[20:50:52 CEST] <JEEB> like, you can have one program that is a data service
[20:50:58 CEST] <JEEB> and has a single data sstream
[20:51:00 CEST] <JEEB> *stream
[20:51:15 CEST] <JEEB> and another that is channel XYZ, which then contains the streams that are in that channel
[20:51:27 CEST] <JEEB> I can give you an example in a momento
[20:51:34 CEST] <benlieb> ok, I just read the wikipedia entry for multiplexing
[20:51:50 CEST] <benlieb> sounds like thats probably a tv broadcast thing that I wont encounter much
[20:51:53 CEST] <benlieb> or at all
[20:52:01 CEST] <JEEB> well, when you put stuff into a container
[20:52:04 CEST] <JEEB> that is multiplexing
[20:52:44 CEST] <JEEB> http://up-cat.net/p/44b45443
[20:53:06 CEST] <JEEB> this example has multiple programs, but only one has actual streams in it
[20:54:59 CEST] <benlieb> so a program can have many streams
[20:55:12 CEST] <JEEB> a program is a set of streams
[20:55:32 CEST] <furq> benlieb: https://trac.ffmpeg.org/wiki/Map#Example8
[20:55:36 CEST] <benlieb> another question& what is the difference between an audio channel and an audio stream?
[20:55:49 CEST] <furq> a stream contains one or more channels
[20:55:51 CEST] <JEEB> audio channel is a single channel from a stream
[20:56:01 CEST] <JEEB> in case of stereo you have two channels
[20:56:03 CEST] <benlieb> can streams have channels?
[20:56:14 CEST] <JEEB> *audio* channels in this context
[20:56:35 CEST] <furq> 5.1 has 6 channels, 7.1 has 8 channels, etc
[20:56:49 CEST] <furq> this is a separate thing really
[20:57:08 CEST] <JEEB> in TV you have channels, and in video context you could say the planes are "channels" as well (R, G, B or Y, Cb, Cr)
[20:57:13 CEST] <furq> right
[20:57:21 CEST] <JEEB> the word "channel" is very context specific in what it means :P
[20:57:40 CEST] <JEEB> although generally it means "a single set of something"
[20:58:01 CEST] <furq> this explains why i can never build a tunnel under the LFE channel
[20:58:15 CEST] <benlieb> Im talking in the context of streams and this:
[20:58:26 CEST] <benlieb> -map_channel [input_file_id.stream_specifier.channel_id|-1][?][:output_file_id.stream_specifier]
[20:58:27 CEST] <benlieb> Map an audio channel from a given input to an output. If output_file_id.stream_specifier is not set, the audio channel will be mapped on all the audio streams.
[20:58:39 CEST] <furq> yeah that extracts one channel from an audio stream
[20:58:46 CEST] <furq> so channel 0 in a stereo stream would be the left speaker
[20:59:12 CEST] <JEEB> also for programs, I think this is the best example I have :D http://up-cat.net/p/e1c01c3f
[20:59:19 CEST] <furq> if you wanted to split left and right speakers into two mono streams, that's one way of doing it
[20:59:20 CEST] <JEEB> of how convoluted MPEG-TS muxes can get
[21:00:04 CEST] <furq> does anything other than mpegts have a concept of programs
[21:00:14 CEST] <benlieb> how do I know how many channels are in a stream, or is only just 1 or 2?
[21:00:16 CEST] <benlieb>  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 135 kb/s (default)
[21:00:16 CEST] <benlieb>   
[21:00:20 CEST] <furq> "stereo"
[21:00:25 CEST] <JEEB> stereo is the layout
[21:00:32 CEST] <JEEB> a layout has a number of channels
[21:01:01 CEST] <benlieb> but how can I see the channels?
[21:01:09 CEST] <benlieb> is 0 left and 1 right?
[21:01:15 CEST] <furq> ffmpeg -layouts
[21:01:25 CEST] <benlieb> I was using ffprobe
[21:01:37 CEST] <furq> -layouts just lists all audio layouts
[21:01:44 CEST] <JEEB> also which channel is which piece of data depends on the layout
[21:01:48 CEST] <furq> ^
[21:01:54 CEST] <furq> stereo is always left then right
[21:02:01 CEST] <furq> but e.g. with 5.1 there's more than one layout
[21:02:08 CEST] <benlieb> ok I see
[21:02:18 CEST] <benlieb> the layout is one of a set type
[21:02:28 CEST] <benlieb> and then ffprobe gives the layout, and I have to lookup what that means
[21:02:34 CEST] <benlieb> somewhat new to all this...
[21:02:45 CEST] <benlieb> is there a grood reference for all of this terminology?
[21:02:48 CEST] <furq> 99% of the time it'll be stereo, 5.1, or 5.1 (side)
[21:02:55 CEST] <benlieb> the ffmpeg docs just assume I know
[21:02:57 CEST] <furq> which is easy enough to memorise
[21:03:10 CEST] <JEEB> benlieb: if you actually use -of json -show_streams -show_programs you will actually get both channel count and layout
[21:03:24 CEST] <JEEB> of json outputs json
[21:03:26 CEST] <furq> you crazy for that json output
[21:03:41 CEST] <JEEB> it seems like the least insane thing to use with most scripting languages
[21:04:25 CEST] <JEEB> because it really sounds like benlieb is trying to parse what ffprobe gives out :P
[21:04:35 CEST] <benlieb> k at jeeb Unrecognized option 'of'
[21:04:42 CEST] <furq> ffprobe
[21:05:29 CEST] <benlieb> ooah
[21:05:31 CEST] <benlieb> got it
[21:05:46 CEST] <furq> -of csv is probably easier if you want this to be human readable
[21:06:14 CEST] <furq> or just -of default
[21:06:15 CEST] <benlieb> Im a software engineer so json is great for me ;)
[21:06:18 CEST] <furq> fair enough
[21:06:24 CEST] <furq> if you want to actually machine parse it then json is what you want
[21:06:52 CEST] <benlieb> json gives labels where the standard output doesnt
[21:06:59 CEST] <benlieb> which is good for a beginner
[21:07:03 CEST] <benlieb> or at least this one
[21:07:05 CEST] <furq> default output should give labels
[21:07:36 CEST] <furq> i wish it didn't because it'd save me having to explicitly turn them off every time i use it in a script
[00:00:00 CEST] --- Sun Jun 24 2018

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