Is there an application or a tool able to display the I/B/P sequence and the GOP length of H.264 files ?
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H.264 GOP length
H.264 GOP length
Last edited by Cantar4 on Wed Jan 03, 2018 4:43 am, edited 3 times in total.
Re: H.264 GOP length
MediaInfo needs sponsors... try this free method instead :
ffmpeg being installed in your CLI terminal, enter
ffprobe -show_frames /(path to the media file) | grep pict_type
you get a list of the I/P/B type of all frames, hence access to the variable length of the GOP due to image variance and compression level.
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Re: H.264 GOP length
Why again was it so important for you to know the GOP sequence?
- Carsten
- Carsten
Re: H.264 GOP length
That's a long story ; before I can explain, have a look at this seven year surrealist fight between the programmer/founder of the open-source VLC and his subscribers : https://forum.videolan.org/viewtopic.php?f=7&t=79893
It finished in blood, and no outcome. I tried to resurrect the thread under more subdued terms but it is now back to the very same 'dialogue de sourds' : https://forum.videolan.org/viewtopic.php?f=7&t=139871
The subject? "frame by frame forward/reverse playback", something that free media players* do for scholars and film addicts of all sorts.
--jp
* QickTime, IINA (for mp4)... and the yesterday's 2.11.52 standalone DoM player (for DCP)
Re: H.264 GOP length
Oh, yes, I see... I am probably spoiled by Quicktime Pro Player. Whenever I use VLC, I sooner or later freak out about missing frame advance/backward keys...
DCP-o-matic has not the best credit there, sometimes it works, sometimes not. Some of it may be OS specific. Very often I try to step back or forward and nothing happens. I don't blame Carl, DCP-o-matic is only possible because of all the underlying framework and libraries, and there is no control down to the final bits of these extremely useful libraries I guess.
I understand both positions - those who say 'hey, can't be so complicated to put a bunch of frames into memory and access them at random', but also those who say 'as a programmer, I tell you the decoder doesn't work that way'.
It's hard to believe it is not possible though. I mean, they built so many redundant functions and options into VLC, hard to believe none of their programmers find a step-back-one-frame useful enough to give it a try. Who cares if it doesn't work for streaming formats? People will usually access frame advance/frame backwards from a paused state. Typically, there is plenty of time to build a playback buffer for this special mode between a pause and a frame command or the next one.
- Carsten
DCP-o-matic has not the best credit there, sometimes it works, sometimes not. Some of it may be OS specific. Very often I try to step back or forward and nothing happens. I don't blame Carl, DCP-o-matic is only possible because of all the underlying framework and libraries, and there is no control down to the final bits of these extremely useful libraries I guess.
I understand both positions - those who say 'hey, can't be so complicated to put a bunch of frames into memory and access them at random', but also those who say 'as a programmer, I tell you the decoder doesn't work that way'.
It's hard to believe it is not possible though. I mean, they built so many redundant functions and options into VLC, hard to believe none of their programmers find a step-back-one-frame useful enough to give it a try. Who cares if it doesn't work for streaming formats? People will usually access frame advance/frame backwards from a paused state. Typically, there is plenty of time to build a playback buffer for this special mode between a pause and a frame command or the next one.
- Carsten
Re: H.264 GOP length
Also have a look at "mpv". It's awesome,
and of course it has step-back-one-frame:
https://mpv.io/
I hardly use anything else nowadays!
and of course it has step-back-one-frame:
https://mpv.io/
I hardly use anything else nowadays!
Re: H.264 GOP length
Do report bugs here: I'd like to try to get frame-seek forward and backward to always work. It's quite dependent on the source file type. I am not doing any of the GPU-related tricks that VLC is doing so my world is a bit simpler than theirs.Carsten wrote: ↑Fri Feb 09, 2018 11:36 pm DCP-o-matic has not the best credit there, sometimes it works, sometimes not. Some of it may be OS specific. Very often I try to step back or forward and nothing happens. I don't blame Carl, DCP-o-matic is only possible because of all the underlying framework and libraries, and there is no control down to the final bits of these extremely useful libraries I guess.
Re: H.264 GOP length
I may need to test it with different content/codec types. Probably I am not bothered often enough. Though I do have to trim clips/trailers often, and usually precisely on scene changes.
One issue that hits people with full length features is that the slider becomes too coarse to navigate quickly and precisely in a project, and then the nudge buttons become too slow to navigate precisely and with decent speed. Something I noticed earlier in OS X was that the nudge buttons often would miss my click actions, thus I thought DCP-o-matic wouldn't move - however, recently stupid me discovered this was actually due to my OS X double click settings. They were already set to an advanced user (rabbit mode), but still too slow to allow real quick nudging in DCP-o-matic. Now I am on 'ARE YOU NUTS?' mode and able to tap near realtime...
I noticed (at least in earlier versions) that sometimes or with some content, the numbers would move on nudging, but not the image. Knowing about interframe compression, I am probably a bit too forgiving about such luxury features...
What I'd love to see is support for SPACE play/pause, cursor key left/right for nudge, and, as some players support it, if you keep a nudge button/cursor key pressed, turn into play mode, or half speed play mode after some delay. Don't know if global simple key actions are possible, though.
- Carsten
One issue that hits people with full length features is that the slider becomes too coarse to navigate quickly and precisely in a project, and then the nudge buttons become too slow to navigate precisely and with decent speed. Something I noticed earlier in OS X was that the nudge buttons often would miss my click actions, thus I thought DCP-o-matic wouldn't move - however, recently stupid me discovered this was actually due to my OS X double click settings. They were already set to an advanced user (rabbit mode), but still too slow to allow real quick nudging in DCP-o-matic. Now I am on 'ARE YOU NUTS?' mode and able to tap near realtime...
I noticed (at least in earlier versions) that sometimes or with some content, the numbers would move on nudging, but not the image. Knowing about interframe compression, I am probably a bit too forgiving about such luxury features...
What I'd love to see is support for SPACE play/pause, cursor key left/right for nudge, and, as some players support it, if you keep a nudge button/cursor key pressed, turn into play mode, or half speed play mode after some delay. Don't know if global simple key actions are possible, though.
- Carsten