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Fix ffmpeg snapshot aspect ratio with auto width#167

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tatsumoto-ren merged 1 commit into
Ajatt-Tools:masterfrom
cnra:agent/fix-ffmpeg-snapshot-aspect
Jul 13, 2026
Merged

Fix ffmpeg snapshot aspect ratio with auto width#167
tatsumoto-ren merged 1 commit into
Ajatt-Tools:masterfrom
cnra:agent/fix-ffmpeg-snapshot-aspect

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@cnra

@cnra cnra commented Jul 9, 2026

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I was trying to create cards with 480px height and auto width.

  • Source video: 1280x720 SAR 3:4 DAR 4:3
  • Expected WebP: 640x480 SAR 1:1
  • Actual result before this fix: 854x480, which appears stretched as WebP

Here is the config I was using:

use_ffmpeg=yes
snapshot_format=webp
snapshot_width=-2
snapshot_height=480

This changes the auto-dimension scale filter to calculate the output size from the display aspect ratio and normalize the snapshot with setsar=1.

@tatsumoto-ren

tatsumoto-ren commented Jul 9, 2026 •
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Source video: 1280x720
Expected WebP: 720/480=1.5, so 1280/1.5=854.

Your webp snapshot should be 854x480, not 640x480. The current behavior appears to be correct.

@cnra

cnra commented Jul 9, 2026 •
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The source video is a little confusing because its stored frame size is 1280x720, which looks like 16:9 at first.

But it has SAR 3:4, so it is not displayed as square-pixel 1280x720. mpv displays it as 4:3, not 16:9.

here is screenshot to be clear with the mpv and the generated image before this fix:
comparison

Here is a clip from video I was working with. ffprobe shows is as 1280x720 with sar SAR 3:4 and it plays as 4:3 not 16:9

25_03m30s-03m40s_sar_sample.mp4

@tatsumoto-ren

tatsumoto-ren commented Jul 10, 2026

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What about regular 1920x1080 videos, such as anime from nyaa.si? Have you checked that generated images are correctly scaled?

@cnra

cnra commented Jul 12, 2026 •
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I tested it with a 1080p video using SAR 1:1, and there were no issues.

Here are the stream details for the tested video:

Stream #0:0[0x1](und): Video: hevc (Main 10) (hev1 / 0x31766568), yuv420p10le(tv, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 754 kb/s, 23.98 fps, 23.98 tbr, 24k tbn (default)
image

@tatsumoto-ren
tatsumoto-ren merged commit c32a748 into Ajatt-Tools:master Jul 13, 2026
@tatsumoto-ren

tatsumoto-ren commented Jul 13, 2026

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Thanks!

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2 participants

@cnra @tatsumoto-ren