Losing 2 frame after upscaling

[christopi]

Losing 2 Frames After Upscaling with Video2X

Description

When upscaling videos using Video2X, the output consistently loses 2 frames compared to the original video. This issue has been observed across multiple tests with varying video durations and frame counts. For example:

• A video with 25 frames outputs 23 frames after upscaling.
• A video with 51 frames outputs 49 frames after upscaling.

This mismatch in frame count makes it impossible to evaluate the upscaled video using VMAF.

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Steps to Reproduce

Follow these steps to reproduce the issue:

1. Use the following commands to upscale a video file:

   • For HEVC input/output:

     video2x -i input.hevc -o output.hevc -p realesrgan -s 2 -c libx265 -e preset=slow -e crf=24

   • For MP4 input/output:

     video2x -i input.mp4 -o output.mp4 -p realesrgan -s 2 -c libx264 -e preset=slow -e crf=24

2. Compare the frame count of the original video and the upscaled video using the following script:

   python scripts/video_info_cap.py

   here is the full script

3. Observe the number of frames in the original and upscaled videos.

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Expected Behavior

The upscaled video should retain the same number of frames as the original video.

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Actual Behavior

The upscaled video consistently loses 2 frames.

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Example Output

Original Video:

=== Video File Information ===
File Path: /workspace/vidaio-subnet/services/upscaling/videos/7579959_hd.mp4
========================================
File Format: mov,mp4,m4a,3gp,3g2,mj2
File Size: 0.21 MB
Duration: 1.00 seconds
Bitrate: 1795.94 kbps
Compressed: Yes

=== Stream Information ===
Stream Type: Video
Codec: h264
Codec Long Name: H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
Resolution: 2049x1080
Frame Rate: 25.00 fps
Number of Frames: 25
Pixel Format: yuv444p
Bitrate: 1786.65 kbps

Upscaled Video:

=== Video File Information ===
File Path: /workspace/vidaio-subnet/services/upscaling/videos/4k_7579959_hd.mp4
========================================
File Format: mov,mp4,m4a,3gp,3g2,mj2
File Size: 0.57 MB
Duration: 0.92 seconds
Bitrate: 5236.69 kbps
Compressed: Yes

=== Stream Information ===
Stream Type: Video
Codec: h264
Codec Long Name: H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
Resolution: 4098x2160
Frame Rate: 25.00 fps
Number of Frames: 23
Pixel Format: yuv444p
Bitrate: 5226.82 kbps

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Environment

• OS: Ubuntu 24.04
• GPU: NVIDIA RTX 6000 Ada Gene...
• Video2X Version: 6.4.0

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Request

Please investigate why Video2X consistently loses 2 frames during the upscaling process and provide a solution to ensure the output retains the same number of frames as the input.

[k4yt3x]

Thanks for the detailed bug report. I'll look into it soon.