[Ffmpeg-devel-irc] ffmpeg.log.20181031

burek burek021 at gmail.com
Thu Nov 1 03:05:02 EET 2018

[00:05:33 CET] <brimestone> is there an FFplay wrapper for objective c?
[00:55:14 CET] <nicolas17> do .ts files have such thing as 'faststart'?
[00:55:31 CET] <furq> no
[00:56:01 CET] <nicolas17> do they not need it? can always play before getting the end?
[00:56:59 CET] <furq> yes
[00:57:08 CET] <furq> the whole point of mpegts is that it's streamable
[00:57:45 CET] <furq> you can start reading from any arbitrary point in the file and it'll play
[00:58:00 CET] <furq> the downside is that sending headers inband adds a lot of overhead and there's no seek index
[00:59:47 CET] <nicolas17> wonder why it was chosen for HLS
[01:00:43 CET] <nicolas17> I guess so that something can produce a long mpegts and something else can chop it up without having to generate new headers or anything?
[01:01:16 CET] <furq> hls is usually used for livestreaming, so it's a pretty natural choice
[01:01:37 CET] <furq> you can use fragmented mp4 as well but that whole format is a bolt-on afterthought
[01:35:40 CET] <Zexaron> Helllo
[01:36:05 CET] <Zexaron> is there a way to detect what kind of build options were used on precompiled .lib files
[01:36:17 CET] <Zexaron> I think I did that in the past but forgot
[01:36:27 CET] <Zexaron> I have like avcodec, avformat etc
[01:36:39 CET] <Zexaron> I have the libs without exe
[01:38:11 CET] <Zexaron> im not sure if precompiled lib is proper term, since it's 8 mb size, but when final project exe is built it's only a like less than 2 mb diff
[01:39:47 CET] <BtbN> avcodec_configuration()
[01:41:34 CET] <Zexaron> oh okay, I was browing through the raw file heh
[01:42:10 CET] <nicolas17> search for "--enable" or "--prefix"? :P
[01:42:19 CET] <BtbN> it's in there somewhere, strings will probably find it
[01:46:57 CET] <Zexaron> yeah not quite getting it const char a = *avcodec_configuration(); debugger a is undefined ... i was in a rush
[01:53:10 CET] <nicolas17> doesn't avcodec_configuration return a char array?
[01:53:17 CET] <nicolas17> const char* a = avcodec_configuration();
[01:54:21 CET] <Zexaron> oh that
[01:55:07 CET] <Zexaron> Yes with VS2017 error reporting I just go trial and error as sometimes the suggestions are so off
[01:59:42 CET] <Zexaron> ain't working either
[01:59:54 CET] <Zexaron> but I can watch avcodec_configuration() directly then
[02:00:14 CET] <Zexaron> using the same code
[02:01:57 CET] <Zexaron> funny how lib file leaks the username of the machine it was compiled in
[02:03:03 CET] <Zexaron> anyway, it's just showing some disassembly and source stuff, not sure if this is it
[02:08:39 CET] <Zexaron> oh okay it's not that big deal, I'll figure it out tomorrow
[02:38:55 CET] <Matador> bloody hecks
[03:08:38 CET] <nicolas17> any idea on how I could get the first frame of an mpegts while reading/downloading as little as possible? I think I would need to parse headers myself to know how big the first packet is and then download only that much...
[03:10:19 CET] <nicolas17> and mpegts headers don't look like the easiest thing to parse ^^
[13:01:07 CET] <Zexaron> Hello
[13:01:22 CET] <Zexaron> does ffmpeg, well, codecs, support changing resulution on-fly ?
[13:01:40 CET] <Zexaron> Probably not but just checking if there's any oddball chance of any codec that can do that?
[13:02:03 CET] <Zexaron> or let's say, input resolution change, but through a filter that scales it to the same output one
[13:03:52 CET] <relaxed> it can decode such streams, not sure about encoding
[13:30:40 CET] <Chagall> just wondering, why is y4m "c420" interpreted as c420jpeg (while c422/c444 have colocated chroma as far as I remember) while c420paldv is interpreted as having colocated chroma instead of the correct pal-dv format?
[13:31:52 CET] <Chagall> it seems like the c420paldv implementation is missing and c420paldv is what c420 should be, though I'm not sure c420 was defined in yuv4mpeg
[13:32:27 CET] <Chagall> that is, the current c420paldv implementation is what c420 should be as it tends to be defined
[13:34:22 CET] <Chagall> I traced back the addition of 420 to this commit https://code.oxygene.sk/mirrors/ffmpeg/commit/b864b38397a2962d265ad39005265bac4fb001ef and I am assuming that LOC_TOPLEFT and LOC_CENTER are exactly what they imply
[13:37:30 CET] <Chagall> in master 420paldv is just treated as a clone of 420mpeg2, and 420 as a clone of 420jpeg (https://code.oxygene.sk/mirrors/ffmpeg/blob/master/libavformat/yuv4mpegdec.c)
[13:39:08 CET] <Zexaron> relaxed: this gave me an idea, if there is a scaling mode that would scale the canvas size not the actual input so it would encode black bars but keep the original input size in place , since this is about frame dumping from a gaming emulator, it's live, it's not offline video, so it may only work if resolution is less than it originally started with
[14:12:19 CET] <blenderwitch> hi! AFAIK, the following command should add image as an attachment stream to mkv container but instead adds it as a video stream: `ffmpeg -i test.mkv -c copy -attach cover.png -metadata:s:t mimetype=image/png test2.mkv`
[14:17:49 CET] <blenderwitch> here's the output of `ffmpeg -i test2.mkv` after the attachment: http://pasted.co/b3e12750
[15:05:08 CET] <blenderwitch> ah, nvm. apparently ffmpeg just shows it weird. mkvinfo does it proper
[15:05:10 CET] <blenderwitch> cheers!
[15:11:36 CET] <lemourin> does avformat have stream preloading built in? that would be useful for http e.g or do i need to implement it myself?
[16:18:20 CET] <pomaranc> identify separate
[18:54:07 CET] <CoreX> best way to go about getting to know if the first and last frames are B frames?
[18:54:53 CET] <furq> ffprobe -show_frames
[18:57:32 CET] <CoreX> thanks
[00:00:00 CET] --- Thu Nov  1 2018

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