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Ask HN: Share your FFmpeg settings for video hosting

72 points indulona | 1 comments | 20 Jul 24 17:30 UTC | HN request time: 0.001s | source

I am working on a website that has video hosting capability. Users can upload video files and i will generate multiple versions with different qualities or just audio, thumbnails and things like that.

I have chosen the mp4 container because of how widely supported it is. To prevent users having to fetch whole files, i use the fast start option, where the container's metadata is written at the beginning of the file, instead of at the end.

Next, I have picked h264 codec because of how widely supported it is. VP8/VP9/AV1/x265/x266 are certainly better but the h264 software encoding is often beating hardware encoding due to highly optimized and time-proven code and supported hardware. And the uploaded videos are already compressed, users won't be uploading some 8k raw videos where most advanced codes would be useful for preserving "quality".

For audio, i have picked opus codec. Seems like good value over others. Not much else to add.

I run the ffmpeg to convert video with command like this:

ffmpeg -hide_banner -loglevel error -i input.mp4 -g 52 -c:v h264 -maxrate:v vbr -bufsize vbr -s HxW -c:a libopus -af aformat=channel_layouts=7.1|5.1|stereo -maxrate:a abr -ar 48000 -ac 2 -f mp4 -movflags faststart -map 0:v:0 -map 0:a:0 output.mp4

where vbr is video bitrate like 1024k(1mbps), abr is audio bitrate like 190k and HxW is video dimensions in case of resizing.

I wonder how are folks that handle video encoding process and generate their videos?

How did you pick your settings, what issues have you encountered and any tips you can share are certainly appreciated.

Quite a niche segment when it comes to operations and not being merely consumer/customer.

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Am4TIfIsER0ppos ◴[21 Jul 24 23:21 UTC] No.41029268[source]▶
For synchronized group watching I typically encode to h264 and aac in mp4. Video: render subtitles if available, downscale to 720p if larger, ensure yuv420p, encode with: preset slow, crf 24, and tune animation or film as appropriate. Copy audio if aac, 2 channel, and bitrate is less than 160k otherwise: force 2 channel, encode at 128k. Fast start is needed otherwise I'd use a separate program to put the "header" at the start.

As for your command line, what do you think -g 52 does? Why do you give conflicting audio channel settings?

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atoav ◴[24 Jul 24 11:24 UTC] No.41055795[source]▶
Ensuring yuv410p is the real important addition of this post. If you don't do that, depending on the user input you will end up with a mp4 that won't play.

AAC is more standard for mp4 video than opus, although I agree opus is the superior CODEC. Whether the benefits of opus outweigh the downsides of it being non-standard in your usecase is not mine to decide, but if you are looking to produce a thing that is similar to most other web video things out there I'd go with AAC. The saved bandwith is probably miniscule in comparison to what you could save on the video side.

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indulona ◴[24 Jul 24 11:50 UTC] No.41055978[source]▶
opus has no issues with support, why go with older aac then?
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1. atoav ◴[24 Jul 24 12:48 UTC] No.41056521{3}[source]▶
Many users of youtube/Vimeo are used to supplying their files like that. Most GUI tools won't have Opus. So if you care about your users delivering already encoded files AAC might be the wiser choice.

This depends on your target audience however

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