求助：FFmpeg去除视频闪烁、裁剪保画质及4K upscale方案

Hey there, I feel your pain—spending a full day debugging FFmpeg commands can be so frustrating, but let's break down your problems and fix them one by one.

1. Cropping While Preserving Original Quality #

You’re right that FFmpeg won’t let you use -c:v copy alongside video filters (since filters require decoding the video first), but we can replicate your original MPEG-2 parameters as closely as possible to minimize quality loss. Your source is 720x576, 25fps, 4224kbps total bitrate—so we’ll match those settings explicitly:

Command for Cropping + Near-Lossless Quality #

ffmpeg -i testinput.mpg -filter:v "crop=468:374:(720-468)/2:(576-374)/2" -c:v mpeg2video -b:v 4224k -r 25 -c:a copy test_cropped_highqual.mpg

• What this does:
  • The crop filter uses calculated offsets (720-468)/2 and (576-374)/2 to target the center of your video (instead of the default top-left corner).
  • We force the video codec to mpeg2video (matching your source) and set the bitrate to 4224k—this keeps visual quality nearly identical to the original.
  • -c:a copy skips re-encoding the audio, saving time and preserving audio quality.

2. Fixing Flickering + Upscaling to 4K/HD #

The flickering you’re seeing is almost certainly from your source being an interlaced MPEG-2 video (standard for old标清 broadcasts). Adjusting brightness/contrast won’t fix this—we need to deinterlace first. For upscaling, we’ll use a high-quality scaling algorithm to avoid pixelation on big screens.

Combined Command: Deinterlace + Crop + 4K Upscale #

We’ll use yadif (a reliable deinterlacing filter) and lanczos (a high-quality scaling filter) for the best results. I recommend outputting to MP4 with H.264 (more efficient for 4K and better supported by modern TVs) instead of MPEG-2:

ffmpeg -i testinput.mpg -filter:v "yadif=1:1:0,crop=468:374:(720-468)/2:(576-374)/2,scale=3840:2160:flags=lanczos" -c:v libx264 -crf 18 -preset medium -c:a aac -b:a 192k test_4k_fixed.mp4

• Key details:
  • yadif=1:1:0: This deinterlaces the video and outputs progressive frames, eliminating that flicker on large screens.
  • scale=3840:2160:flags=lanczos: Scales your cropped video to 4K using the Lanczos algorithm, which preserves sharpness better than basic scaling.
  • libx264 -crf 18: H.264 encoding with a CRF (Constant Rate Factor) of 18 gives near-lossless quality while keeping file sizes manageable.
  • preset medium: Balances encoding speed and compression efficiency—adjust to slow for better compression (or fast if you need speed).
  • If you must output MPEG-2 (.mpg), replace the video codec part with -c:v mpeg2video -b:v 20M (MPEG-2 is less efficient, so you’ll need a much higher bitrate to maintain 4K quality).

Quick Notes #

• If you prefer HD (1080p) instead of 4K, change the scale value to 1920:1080.
• Test the deinterlacing first with a short clip to confirm it fixes the flickering—you can tweak the yadif parameters if needed (e.g., yadif=0:0:0 for simpler deinterlacing).

内容的提问来源于stack exchange，提问作者Sabha