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FFMPEG from Zero to Hero

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Re: FFMPEG from Zero to Hero

#51

Post by Cogito »

shazmosushi wrote: post #47
walrus01 wrote: post #44

Earlier quoted context omitted.

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, sc…

When I ran into this, it came down to if I wanted to splice two videos together, or re-encode them.

Due to how keyframes work, cutting on keyframe boundaries is a lot faster and easier and doesn't require re-encoding in many cases. This is the default for the segment muxer.

Cutting between keyframes is a fair bit more effort, and requires re-encoding, which is why I guess it's not the default.

Re: FFMPEG from Zero to Hero

#52

Post by walrus01 »

shazmosushi wrote: post #47
walrus01 wrote: post #44

Earlier quoted context omitted.

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, sc…

I understand that you want to do that, but any attempt to do so will be decidedly non-optimal due to how keyframes and lossy encoders work.

Even if your two files were encoded with x265 at exactly the same bitrate. It's a much more complicated problem than it appears at first glance, once you really dig into the command line options and encoding parameters of codecs like x264, x265 and vp9.

It's not as simple as concatenating two files together. You can also select down to per-frame precision using kdenlive and loading different x264,x265,vp8,vp9 files into it and cutting/editing them together. You will then need to re-encode the resulting output. kdenlive is ultimately a nice GUI front end on top of this:

https://www.mltframework.org/

Re: FFMPEG from Zero to Hero

#53

Post by Noctem »

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…

ffmpeg seeks accurately when transcoding. [1] Cutting on non-keyframes when stream copying results in broken video until the next keyframe.

Handbrake does have a CLI. [2] I haven't used it and I'm not sure what advantage it might have over ffmpeg. I personally use mkvmerge or ffmpeg for my muxing/cutting and VapourSynth for encoding.

[1] https://trac.ffmpeg.org/wiki/Seeking

[2] https://handbrake.fr/docs/en/latest/cli/cli-options.html

Re: FFMPEG from Zero to Hero

#54

Post by magicalhippo »

molticrystal wrote: post #30
Confiks wrote: post #2

Might have come in handy while I was struggling to type out ffmpeg -i part0.mp4 -i part1.mp4 -filter_complex "[1:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2[v1]; [0:v] [0:a] [v1] [1:a] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" out.mp4 to concatenate two videos with different sizes today. My relation with it is almost identical to my relation with any bash scripting m…

I never had to use it since I never had anything complicated enough, but next time you relearn things, I've heard good things about ffmpeg-python [0] , it supports multiple inputs, outputs, custom filters, etc. Their example from the readme: ffmpeg -i input.mp4 -i overlay.png -filter_complex "[0]trim=start_frame=10:end_frame=20[v0];\ [0]trim=start_frame=30:end_frame=40[v1];[v0][v1]concat=n=2[v2];[1]hflip[v3];\ [v2][v…

At this point I'd prefer it if ffmpeg included Lua and allowed you to pass Lua scripts, kinda like what ZFS did[1].

[1]: https://zfsonlinux.org/manpages/0.8.3/man8/zfs-program.8.htm...

Re: FFMPEG from Zero to Hero

#57

Post by umaar »

Noctem wrote: post #53
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…

ffmpeg seeks accurately when transcoding. [1] Cutting on non-keyframes when stream copying results in broken video until the next keyframe. Handbrake does have a CLI. [2] I haven't used it and I'm not sure what advantage it might have over ffmpeg. I personally use mkvmerge or ffmpeg for my muxing/cutting and VapourSynth for encoding. [1] https://trac.ffmpeg.org/wiki/Seeking [2] https://handbrake.fr/docs/en/latest/cli…

I battled with this a lot with https://github.com/umaar/video-everyday and still haven't found a better solution.

What I don't understand is, how can professional video editing tools trim accurately (and very quickly)? What are they doing differently to ffmpeg?

If do things the "fast way" with ffmpeg, the exported video has random black frames which I think is related to the keyframe issue you mention. If I do things the "slow way" (e.g. accurately) with ffmpeg, it takes a huge amount of time (at least with large 4k videos). But I don't understand how I can drop that same 4k video into Screenflow, trim 1 second out of it and export it in a matter of seconds.

Re: FFMPEG from Zero to Hero

#58

Post by inopinatus »

herpderperator wrote: post #11
Confiks wrote: post #2

Might have come in handy while I was struggling to type out ffmpeg -i part0.mp4 -i part1.mp4 -filter_complex "[1:v]scale=1280:720:force_original_aspect_ratio=decrease,pad=1280:720:(ow-iw)/2:(oh-ih)/2[v1]; [0:v] [0:a] [v1] [1:a] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" out.mp4 to concatenate two videos with different sizes today. My relation with it is almost identical to my relation with any bash scripting m…

It's true, and I feel the same, but to give it some credit: wouldn't that apply to anything you don't use regularly? Programming languages or even regular languages. You have to use it or lose it.

You don’t lose it completely. It rusts over, but I had occasion recently to resurrect my 6502 assembler, and it was still in muscle memory.

Kinda like running into an old friend you haven’t seen in decades.

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