FFmpeg技术问题：如何将视频从1917×1080 resize并pad至1920×1080？

Hey Jules, let’s figure out why your pad operation isn’t sticking, and address that initial vertical source size concern—it’s definitely playing a role here!

First, Let’s Diagnose the Problem #

Your initial video is 640×1136 (vertical), which after rotation, resize, and audio merging ended up at 1917×1080. The 3-pixel width gap you’re trying to pad isn’t being fixed likely because of one of two issues:

• Your filter chain order in previous steps caused unintended dimension locking
• You’re applying the pad as a separate step instead of integrating it with your other video manipulations

Why the Initial Vertical Size Matters #

Vertical-to-horizontal conversion needs careful ordering of operations. If you rotated after resizing, or resized without accounting for the aspect ratio shift from rotation, you ended up with that odd 1917×1080 dimension instead of cleanly hitting your target. Fixing the workflow order will eliminate this headache.

The Solution: Combine All Video Operations in One Filter Chain #

Instead of splitting rotation, resize, and pad into separate commands, bundle them into a single filter_complex call. This ensures each step passes the correct dimensions to the next. Here’s a tailored command for your use case:

-i your_vertical_source.mp4 -i your_audio_file.mp4 -filter_complex "[0:v]rotate=PI/2:ow=ih:oh=iw[v_rot];[v_rot]scale=1920:1080:force_original_aspect_ratio=decrease[v_scaled];[v_scaled]pad=1920:1080:(ow-iw)/2:(oh-ih)/2:color=black[v_final]" -map "[v_final]" -map 1:a -c:a copy final_output.mp4

Let’s break down each filter step:

1. Rotate: rotate=PI/2:ow=ih:oh=iw converts your vertical 640×1136 video to horizontal 1136×640, explicitly setting output width/height to match the rotated aspect.
2. Scale: scale=1920:1080:force_original_aspect_ratio=decrease resizes the rotated video to fit within 1920×1080 without stretching—this is why you ended up at 1917×1080 before (it’s the closest proportional fit).
3. Pad: pad=1920:1080:(ow-iw)/2:(oh-ih)/2 adds equal black bars to the left/right to fill the 3-pixel gap, centering your video perfectly.

If You Still Want to Use Your Existing Intermediate File #

If you don’t want to reprocess from scratch, verify your intermediate video’s actual dimensions first with:

-i your_1917x1080_video.mp4

Then apply the pad directly with this simple command (make sure there are no conflicting filters from previous steps):

-i your_1917x1080_video.mp4 -vf pad=1920:1080:(1920-iw)/2:(1080-ih)/2:color=black -c:a copy padded_output.mp4

Key Takeaway #

Your initial vertical source size was indeed a contributing factor—rotating after resizing can throw off aspect ratio calculations. By handling rotation → scaling → padding in one continuous filter chain, you avoid dimension discrepancies and ensure your final video hits the exact 1920×1080 resolution you need.

内容的提问来源于stack exchange，提问作者Jules