frames not synched with alternative video proxy way

Qbrick wrote on 5/12/2025, 2:42 AM

Hi all,

I'm trying to use an alternative way for video proxy.

I like the "Add Proxies as Takes.cs" from https://vegasaur.com/bin/scripts but I noticed a strage/wrong thing.

Sometimes frames are not synched when I switch from take "original" to take "proxy" .

So I checked with Avisynth+/AVSPmod:

clipv1=FFmpegSource2("video.mp4", vtrack = -1)

clipv2=FFmpegSource2("video.mp4.sfvp0", vtrack = -1)

clipv1r=BilinearResize(clipv1, clipv2.width,clipv2.height)

StackHorizontal(clipv1r, clipv2)

Frames btw 2 videos are perfectly synched!

So what's wrong?

- something on Magix Vegas?

- something with script "Add Proxies as Takes.cs" ?

Thanks!

this is the ffmpeg command to generate proxy files:

ffmpeg -hide_banner -hwaccel cuda -hwaccel_output_format cuda -copyts -i "video.mp4" -map 0:0 -fps_mode passthrough -c:v h264_nvenc -g 1 -preset p1 -vf "scale_cuda=-2:256:format=yuv420p:interp_algo=bilinear,setpts=PTS-STARTPTS -f mp4 "video_proxy.mp4"

Comments

Qbrick wrote on 5/12/2025, 3:10 AM

with this command the unsynched frames not happen:

ffmpeg -i video.mp4 -c:v mpeg2video -brand mp42 -vf "scale=-2:256" -qscale:v 5 -an -f mp4 video.mp4

But I can't use GPU/CUDA to create proxy files :(

johnny-s wrote on 5/12/2025, 12:57 PM

Back again. I found issues using hwaccel previously, cannot at this remove remember exactly what but decided to not use. Is faster because everything is kept in gpu.

I admire your perseverance in attempting to get VP te proxies to work, created externally.

#1. However I think creating simple Avc proxies externally is my preference if I had to with say 8k or some very difficult hevc footage.

Some cameras give option to also save smaller fhd avc proxies on say second SD card. This is similar in outcome to #1.

I think then using the Swap method or user 3d87c4's method is the way to go with say FHD proxies.

I don’t think there is any intrinsic benefit to using vp type proxies unless for a short project.

Important to not overlook that the default gop for avc h264 generation is 250. Setting this to something like source frame rate is nearly a must.

As far as as I can remember old mpeg2 used something like 12. Smaller is easier on timeline. Must check what vp proxy is.

johnny-s wrote on 5/12/2025, 1:29 PM

VP proxy GOP is indeed 12, layout is IBBP for proxy output from S24 8K clip.