Learn FFmpeg the hard way

#1

Post by dreampeppers99 » Sat, Jan 20, 2018, 9:58 AM UTC

Re: Learn FFmpeg the hard way

#2

Post by seertaak » Sat, Jan 20, 2018, 11:27 AM UTC

This is awesome -- I read the first few pages and I'm really looking forward to reading the rest. Very clearly explained; thanks for creating/sharing!

Re: Learn FFmpeg the hard way

#3

Post by jakalah » Sat, Jan 20, 2018, 11:33 AM UTC

i have used it on the commandline really gives you fine grained control. winff is a easy way and almost as good within the front end.nice article on it.

Re: Learn FFmpeg the hard way

#4

Post by spython » Sat, Jan 20, 2018, 12:10 PM UTC

I wrote about creating adaptive streaming over HTTP (MPEG-DASH) using ffmpeg and mp4box before [1]. It is nice to see that ffmpeg is incorporating more and more of the same features.

Has anybody got ffmpeg to create HLS out of mp4 fragments as well? It would save some conversion time and space, since the same MP4 fragments could be used with the two different manifest files, DASH and HLS. Mp4box is not quite there yet, sadly.

[1] https://rybakov.com/blog/mpeg-dash/

Re: Learn FFmpeg the hard way

#5

Post by sbarre » Sat, Jan 20, 2018, 12:30 PM UTC

This looks pretty awesome..

I was hoping this was about the command-line tool, which is quite daunting to learn once you start getting into the filters and combining/merging multiple audio and video sources.

In a recent project I eventually had to write a script to do 2 passes of ffmpeg after spending a good day trying to figure my way through all the filter documentation to do a 5-step process in one pass..

This isn't a knock against ffmpeg, which is an amazing open source package, but it's complicated, so I'm sure this repo will be of great help to many.

Re: Learn FFmpeg the hard way

#6

Post by anonymfus » Sat, Jan 20, 2018, 12:36 PM UTC

>In summary this is the very basic idea behind a video: a series of pictures / frames running at a given rate.

>Therefore we need to introduce some logic to play each frame smoothly. For that matter, each frame has a presentation timestamp (PTS) which is an increasing number factored in a timebase that is a rational number (where the denominator is know as timescale) divisible by the frame rate (fps).

Constant framerate is a very dangerous assumption to make. It's true for video recorded by professional cameras, but if you check video recorded by most mobile phones you notice that it's wrong.

Re: Learn FFmpeg the hard way

#7

Post by jsdir » Sat, Jan 20, 2018, 1:04 PM UTC

My project ran into a limitation that required only the use of FFmpeg libav without the command line tool. This is exactly what I needed. I'm eager to read the rest.

Re: Learn FFmpeg the hard way

#8

Post by gowan » Sat, Jan 20, 2018, 1:33 PM UTC

anonymfus wrote: post #6

>In summary this is the very basic idea behind a video: a series of pictures / frames running at a given rate. >Therefore we need to introduce some logic to play each frame smoothly. For that matter, each frame has a presentation timestamp (PTS) which is an increasing number factored in a timebase that is a rational number (where the denominator is know as timescale) divisible by the frame rate (fps). Constant framer…

to be fair it is possible to do this from the command line with ffmpeg when using concat[1][2]. i did this when creating real time video from screencast in the chrome remote debugger.

[1] https://ffmpeg.org/ffmpeg-formats.html#concat

[2] https://trac.ffmpeg.org/wiki/Slideshow

Re: Learn FFmpeg the hard way

#9

Post by jiggunjer » Sat, Jan 20, 2018, 1:33 PM UTC

anonymfus wrote: post #6

>In summary this is the very basic idea behind a video: a series of pictures / frames running at a given rate. >Therefore we need to introduce some logic to play each frame smoothly. For that matter, each frame has a presentation timestamp (PTS) which is an increasing number factored in a timebase that is a rational number (where the denominator is know as timescale) divisible by the frame rate (fps). Constant framer…

In my experience even cameras with constant framerates aren't really constant, if you look at the timestamps the delay between frames typically varies a few (dozen) ms. So on average you might have 30fps, but if you sample a random second you might end up with 28-32 frames.

Re: Learn FFmpeg the hard way

#10

Post by lovelearning » Sat, Jan 20, 2018, 1:55 PM UTC

anonymfus wrote: post #6

>In summary this is the very basic idea behind a video: a series of pictures / frames running at a given rate. >Therefore we need to introduce some logic to play each frame smoothly. For that matter, each frame has a presentation timestamp (PTS) which is an increasing number factored in a timebase that is a rational number (where the denominator is know as timescale) divisible by the frame rate (fps). Constant framer…

[1] is a useful list of such assumptions. Found it very handy when programming AV handling.

[1]: https://haasn.xyz/posts/2016-12-25-falsehoods-programmers-be...