[Ffmpeg-devel-irc] ffmpeg.log.20181206

[burek]

[01:04:50 CET] <amflir> `ffmpeg -i foo.mov bar.mov` changes the size of file from 200mb to 15mb for me. I can hardly see any quality difference by eyes. I am just deciding to which version to store?
[01:05:06 CET] <devp> Hello. I've got a MPD file with segmets of video and audio, there's some way to take just the audio segments?
[01:05:17 CET] <amflir> actually what happens? why it compresses the file so much? and what I lose?
[01:35:50 CET] <amflir> why concating videos with ffmpeg concat filter (and -c copy) produces a larger output than cat a.mts b.mts>c.mts ?
[01:38:04 CET] <DHE> amflir: if you don't specify codecs and options thereof, ffmpeg uses defaults. they might not be smart defaults, but they're functional...
[01:41:09 CET] <amflir> DHE, when I don't reencode (use -c copy) what exactly changes that makes the output larger?
[01:42:51 CET] <DHE> mpegts has a LOT of muxing overhead. 10% is somewhat normal, and some types are optional or just repeated frequently.
[01:43:28 CET] <DHE> eg: ffmpeg's mpegts defaults are designed to be friendly to streaming/broadcast uses. you can knock a bit off the file size if you change that.
[04:40:15 CET] <fraktor> I'm trying to extract some audio from another file using ffmpeg to do some processing with it, but it's quite long, so WAV files don't quite work properly. What's another uncompressed format that I can use?
[04:42:52 CET] <furq> flac?
[04:43:04 CET] <furq> if "don't work properly" means you're running out of disk space
[04:44:58 CET] <fraktor> WAV headers can only support files up to 4gb, so it's more that the file format is problematic.
[04:45:07 CET] <furq> oh right yeah
[04:45:09 CET] <furq> well flac should work fine
[04:45:33 CET] <furq> or mka if you specifically need uncompressed
[04:45:35 CET] <fraktor> I wanted something uncompressed, so that conversion would be fast. I found out how to use raw pcm data, which audacity can read, so I went with that.
[09:33:23 CET] <th3_v0ice> How can I get how long in seconds a video is, AVFormatContext->duration / AV_TIME_BASE should do it, right?
[12:15:54 CET] <X-Kent> hi, I am using ffplay to play hls. source m3u8 has 10 segments available. ffplay starts playing from the last 3 segments. Can I somehow force it to start from the first segments ? (as in case of last 3 it stalls if any of the segments doesn't arrive in time)
[12:16:04 CET] <X-Kent> it's a live stream
[12:29:17 CET] <X-Kent> found it, it's live_start_index
[14:16:47 CET] <DHE> X-Kent: sounds like the playlist is badly formatted. it should indicate it's an EVENT/VOD type, or have an EXT-X-ENDLIST tag indicating it's complete. otherwise it's assumed to be a live/updating event and played near the end
[14:17:57 CET] <X-Kent> DHE, it is a live playlist, I found the solution, it's "-live_start_index", it wasn't in the manpage so took time to figure out
[14:21:01 CET] <DHE> oh, you did say that. oops...
[14:21:23 CET] <DHE> yeah default behaviour is to start at close to live as realistically possible. 3 segments are for buffering purposes.
[15:15:56 CET] <alexpacio_> how can I tell ffmpeg to use libva (VA-API acceleration) by default?
[16:22:31 CET] <devp> Hello. I need split an audio from video source, I did download it from a streaming. The audio is encoded into the video source with a range of bytes indicated through of a .mpd file. How i could get just the audio ?
[16:23:37 CET] <pink_mist> ffmpeg -i file.ext audio.mp3
[16:24:51 CET] <DHE> that transcodes the audio to mp3, which may or may not be what you want
[16:26:31 CET] <pink_mist> yeah, alternatively you could figure out what the actual encoding is and use -c:a copy foo.<appropriate audio extension> but I didn't want to haveto write that much, but now you made me do it anyway =(
[16:26:53 CET] <devp> exactly.. The source has the audio encoded just in a little bytes and that bytes are indicated in a mpd file
[16:27:11 CET] <pink_mist> "in a little bytes" is not an audio encoding
[16:32:07 CET] <devp> And i could split a video/audio from encrypted source ?
[17:16:28 CET] <DHE> devp: ffmepg has some encryption support. if the key is obtainable, maybe.
[17:41:25 CET] <FurretUber> Is there a way to record a specific window with FFmpeg? Using Xubuntu 18.04, Xorg. I know there is a way to set resolution and coordinate, but I wanted to set by window title, if possible
[17:42:28 CET] <DHE> doesn't look like it. see: ffmpeg -h demuxer=x11grab
[17:42:49 CET] <DHE> none of these options seems appropriate, other than helping you line it up with a capture border
[17:55:28 CET] <BtbN> There isn't really an API to do that either
[17:55:47 CET] <BtbN> OBS does it by just tracking position and size and then cropping a full screen capture
[17:56:07 CET] <BtbN> Or via (ab)using XComposite extensions to grab a specific windows texture
[17:57:51 CET] <Alina-malina> can someone give me the command of how correctly to download the desktop and sound?
[18:00:24 CET] <Zgrokl> is it possible to pipe screen shot >> ffmpeg in realtime with multithread
[18:00:31 CET] <Zgrokl> actually it's working monothread
[18:00:39 CET] <Zgrokl> maybe because ffmpeg wait on the screenshot app
[18:01:16 CET] <Zgrokl> but i want to habe speed = 1x
[18:02:15 CET] <BtbN> That sounds like worlds most inefficient screen recording.
[18:02:35 CET] <Alina-malina> well i need to record the sound from firefox browser
[18:02:37 CET] <Alina-malina> maybe it has some pipe?
[18:02:52 CET] <BtbN> Use OBS
[18:42:42 CET] <Alina-malina> ye tried it, but its not convenient, i wish i could record the same with ffmpeg :-/ but thanks for tip bro, btw mate this is the quality i made with OBS https://youtu.be/4FlfLesMzLc  BtbN
[18:43:32 CET] <BtbN> so? Encoder settings are identical for obs and ffmpeg. Since obs uses ffmpeg as encoder.
[18:44:01 CET] <Alina-malina> what about CPU usage?
[18:44:31 CET] <Alina-malina> i thought that ffmpeg is less eating resources, anyways thanks for tip, this is great program, i think i can stream with it as wel?
[18:44:34 CET] <Alina-malina> well*
[18:45:05 CET] <Alina-malina> with ffmpeg i could add slides fade in/ fade out and some other effects, so much get used to it already
[18:47:46 CET] <BtbN> That's usually what you use OBS for, not ffmpeg. Since doing that is insanely annoying with just ffmpeg cli
[18:50:39 CET] <Alina-malina> well i already got used to it hehe
[20:25:15 CET] <halvard> Hi I tried to convert a mkv to mp4, but got the error "Could not write to header for output file". I used just the simple command ffmpeg -i <input> -codec copy <output>
[20:25:35 CET] <JEEB> the actual error is somewhere before that
[20:25:44 CET] <JEEB> post full terminal log on pastebin or similar
[20:25:46 CET] <JEEB> link here
[20:26:10 CET] <halvard> Codec frame size is not set, probably.
[20:26:14 CET] <halvard> Will do :)
[20:27:40 CET] <halvard> https://pastebin.com/S5K6FeZx
[20:29:17 CET] <DHE> line 31 pretty much says it all
[20:29:44 CET] <JEEB> except of course everyone prefers -strict experimental instead of -2 :P
[20:29:52 CET] <DHE> either add the -strict option just before the output filename, or transcode the audio to another code
[20:29:54 CET] <DHE> *codec
[20:30:12 CET] <JEEB> also I'm not sure if the opus muxing of 3.4.x is up to snuff
[20:32:34 CET] <JEEB> seemms like there were some improvements semi-recently
[20:32:43 CET] <JEEB> this probably the biggest one http://git.videolan.org/?p=ffmpeg.git;a=commit;h=7890181d7e76a74fdb7a50785fc4178ed8491171
[20:34:02 CET] <halvard> At least one output file must be specified
[20:34:42 CET] <kepstin> maybe that message ffmpeg prints for the "support is experimental" should have an "or upgrade to a newer ffmpeg version" added to the end of it :)
[20:41:38 CET] <pink_mist> kepstin: how can an old version of ffmpeg know that a newer one will not have the support be experiemental still?
[20:41:48 CET] <pink_mist> *experimental
[20:43:04 CET] <halvard> Artificial Intelligence
[21:24:52 CET] <Seethe> Hi, i'm trying to add two audio streams (both work independently, encoded in reaper as pcm) into an mp4 container. ffmpeg seems to be setting the codec improperly to an ascii square. here's the command: https://pastebin.com/MhJwLHLe (ffmpeg.pastebin is down?)
[21:57:39 CET] <BtbN> I'm pretty sure mp4 can't contain wav
[21:59:44 CET] <JEEB> there's raw audio defined for it, but it's not often supported by other stuff
[00:00:00 CET] --- Fri Dec  7 2018