Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

FFMPEG from Zero to Hero

ffmpegfromzerotohero.com

Post reply on HN
Print view View original

41–50 of 140 posts

Re: FFMPEG from Zero to Hero

#41

Post by walrus01 »

One of the interesting things you can do with ffmpeg, if you have a LOT of scratch disk space, and you're trying to compare subjective encoder quality (not VMAF, but human eyeballs) on a certain video file:

1) take your raw uncompressed y4m file and write it out to a directory of PNG files, one png file per frame. this is your static image reference baseline for subjective eyeballs.

2) take your raw uncompressed y4m file and encode it to x265 or whatever codec you're testing, at various different bitrates and encoder settings

3) take your various encoded x265 files and also write those out to PNG files in separate directories

3) pick exactly the same frame number filename from your 'master' PNGs and your encoder-output PNGs, copy them and put them in the same directory so you can quickly flip back and forth between them in a image slideshow application.

If you want to do this with 2160p24,p25 or p30 videos at several minute lengths, be prepared to have 150-160GB of scratch disk per y4m and per PNG-dump-directory.

Re: FFMPEG from Zero to Hero

#42

Post by tartoran »

I use ffmpeg regularly to cut and join videos and it saves me so much time to run my scripts. I’d give up if I had to fire up some GUI and pick and tick one million settings. Admittedly, creating the script is not different but the reuse is the usecase and it does pay off so nicely

Re: FFMPEG from Zero to Hero

#43

Post by shazmosushi »

I love FFMPEG, but it has truly awful handling of timestamps by default. You can't easily extract a clip using an exact timestamp because it rounds to the nearest keyframe, which may be many seconds earlier. It's such a powerful command-line tool, but I find the user-interface far more difficult than it needs to be. In "git" terminology, there's so much plumbing but not enough porcelain

I wish there was a scriptable / command-line interface for HandBrake (which is already based on FFMPEG) [1], where the user just provides the high-level commands: 99% of the time I want to specify high-level commands: extract clip from this timestamp, including SRT subtitles, crop to this geometry, and shift the audio by 3 seconds.

[1] https://en.wikipedia.org/wiki/HandBrake

Re: FFMPEG from Zero to Hero

#44

Post by walrus01 »

shazmosushi wrote: post #43

I love FFMPEG, but it has truly awful handling of timestamps by default. You can't easily extract a clip using an exact timestamp because it rounds to the nearest keyframe, which may be many seconds earlier. It's such a powerful command-line tool, but I find the user-interface far more difficult than it needs to be. In "git" terminology, there's so much plumbing but not enough porcelain I wish there was a scriptable…

If you have sufficient scratch disk space you can absolutely use ffmpeg to take input of a h264, h265, vp8 or vp9 file, or just about anything else, and write it out to a y4m format uncompressed, raw yuv420p or yuv422 file. From there you can use just about any industry standard commercial or free GUI based video editing tool (kdenlive, etc) to extract a clip, down to per-frame precision.

Re: FFMPEG from Zero to Hero

#47

Post by shazmosushi »

walrus01 wrote: post #44
shazmosushi wrote: post #43

I love FFMPEG, but it has truly awful handling of timestamps by default. You can't easily extract a clip using an exact timestamp because it rounds to the nearest keyframe, which may be many seconds earlier. It's such a powerful command-line tool, but I find the user-interface far more difficult than it needs to be. In "git" terminology, there's so much plumbing but not enough porcelain I wish there was a scriptable…

If you have sufficient scratch disk space you can absolutely use ffmpeg to take input of a h264, h265, vp8 or vp9 file, or just about anything else, and write it out to a y4m format uncompressed, raw yuv420p or yuv422 file. From there you can use just about any industry standard commercial or free GUI based video editing tool (kdenlive, etc) to extract a clip, down to per-frame precision.

But why is that multi-step process even necessary?

There should be an quick command-line utility to concatenate multiple video files according to exactly the timestamps the user has provided. It's such a common operation.

There's no reason that the tool can't simply do a streaming decode of multiple different file formats and concatenate the video and sub-second precision. If input video resolutions are different, scaling the smaller video to the largest resolution is what the user almost always wants.

I get that FFMPEG is a "plumbing" CLI tool, but a "porcelain" wrapper would be amazing!

Re: FFMPEG from Zero to Hero

#48

Post by lmohseni »

lgeorget wrote: post #27
amelius wrote: post #13

Earlier quoted context omitted.

I just grep through my bash history ;)

I have a $HOME/bin folder full of bash scripts invoking imagemagick or ffmpeg one liners.

One handy idiom I like to use after typing out a long command that I might want to save is

    echo ‘!!’ > ~/bin/name-of-script
where !! is the previous command

Re: FFMPEG from Zero to Hero

#49

Post by miles »

> Tested for MacOS X, Ubuntu 18.04, Ubuntu 20.04 and Windows 10 platforms

I'm always surprised at how often macOS is misprinted, especially in technical publications. I suppose Apple hasn't made it easy to keep up (Mac OS, Mac OS X, OS X[1]), but macOS has been the official name since Sierra[2]. Perhaps it shouldn't, but it does make me wonder about the accuracy of other details a publication might offer.

[1] https://en.wikipedia.org/wiki/MacOS

[2] https://en.wikipedia.org/wiki/MacOS_Sierra

Re: FFMPEG from Zero to Hero

#50

Post by motohagiography »

hardwaregeek wrote: post #4

If this book does what it claims to do, it should probably cost more (pls raise the price after I buy it). I strongly believe that inside ffmpeg may be the secret to the cosmos, the universe and life itself

Read this thread to say this. ffmpeg is one of the most unbelievable FOSS efforts I have ever used. I am in almost constant daily awe of imagemagick and this.
Post reply on HN