[FFmpeg-user] resize file and output larger

[Moritz Barsnick]

On Tue, Oct 22, 2019 at 14:18:17 +0200, Michele Salerno wrote:
> Hi, i have this command:
>
> ffmpeg -threads 16 -hwaccel nvdec -hwaccel_output_format cuda -i
> input.mp4 -vf scale_cuda=720:480 -c:v h264_nvenc -preset slow
> output.mp4
>
> and output
> https://pastebin.com/vDL3rLF5?fbclid=IwAR2zk5MbBveBrdp5nhPuSyLhUvdds0VjBgPG3hgpzZhCCcj4C0YZKMs9rRc

That's so little text, you might as well have posted it here (pastebin
content tends to disappear). Fixing that for you:

#Originale
Duration: 00:15:27.49, start: 0.000000, bitrate: 965 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 830 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)

#Convertito
Duration: 00:15:27.48, start: 0.000000, bitrate: 2131 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 720x480 [SAR 1:1 DAR 3:2],  1999 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 127 kb/s (default)

> because the output file is larger than the original?

I don't use nvenc, but this comment seems in line with your result:
https://superuser.com/a/1369307

    "My experience with using nvenc is that you need to tell it what
    bitrate you want -- it defaults to VBR, which is fine, but no
    amount of tuning makes up for the fact that it always wants to give
    you a 2M average bitrate no matter what resolution file you feed
    it."

You may want to try some varying encoder options instead.

Good luck,
Moritz