mpeg2 progressive - remove duplicate frames, but no reencode?

[cinephil]

The source is DVD with PAL to NTSC conversion done not like usual telecine, but adding 1 duplicate frame after every 5 or 6 frames. Is it possible to remove duplicate frames but no reencode?

[videoAI]

Yes, it is possible to remove duplicate frames without re-encoding the video.
The specific technique involves using the `mpdecimate` filter, which can
detect and remove duplicate frames with minimal quality loss.

ffmpeg -i input.dvd.mkv -vf mpdecimate -vsync passthrough output.mkv

Key Parameters Explained
- `-vf mpdecimate` : The video filter that detects and removes duplicate frames
- `-vsync passthrough`: Ensures the frame rate is preserved after duplicate removal

Additional Considerations
- The `mpdecimate` filter works best when duplicates are exact matches
- For your specific scenario (1 duplicate after every 5-6 frames), this might require some fine-tuning
- You may need to adjust parameters like `max=1` to control duplicate frame detection

If the basic command doesn't work perfectly, you can add more precise parameters:

ffmpeg -i input.dvd.mkv -vf "mpdecimate=max=1:hi=64:lo=64" -vsync passthrough output.mkv

if you rather use a GUI, try Clever FFmpeg-GUI

[cinephil]

Yes, it is possible to remove duplicate frames without re-encoding the video.
The specific technique involves using the `mpdecimate` filter, which can
detect and remove duplicate frames with minimal quality loss.

If there is no re-encoding, where is "quality loss" came from?

if you rather use a GUI, try Clever FFmpeg-GUI

I leaning more to GUI, but not see how to use filters in Clever FFmpeg-GUI

[Alwyn]

I'm no expert but I can't see any way of not re-encoding if you start removing frames.

If you're into AVISynth, 1 in 6 decimation seems to work (with Ass to increase the speed from 24.975 after the Tdec to 25):

LWLibavVideoSource("sample2.m2v")
TFM()
TDecimate(Cycle=6, CycleR=1)
AssumeFPS(25)

[cinephil]

I'm no expert but I can't see any way of not re-encoding if you start removing frames.

I thought that mpeg2 allows cut/join (to the frame accuracy) without re-encode?

[poisondeathray]

I'm no expert but I can't see any way of not re-encoding if you start removing frames.

I thought that mpeg2 allows cut/join (to the frame accuracy) without re-encode?

For I-frame only encoded mpeg2 , yes

For you - no, because it's a long gop encode (some frames reference data from adjacent frames). Whenever you interrupt or edit within a GOP, the entire GOP must be re-encoded

[cinephil]

For I-frame only encoded mpeg2 , yes

For you - no, because it's a long gop encode (some frames reference data from adjacent frames). Whenever you interrupt or edit within a GOP, the entire GOP must be re-encoded

Yeah... I guess I remembering those programs that re-encode only split section and direct stream copy the rest. But since splits is every 6 frames - it's not make much sense in here

[videoAI]

Let me help clarify this for you by breaking down the nuances of frame decimation and video processing.

When using the `mpdecimate` filter, there are actually two potential scenarios of "quality" impact:

1. Computational Processing
- The `mpdecimate` filter analyzes and removes duplicate frames
- This process itself does not re-encode or modify the video's actual visual quality
- The computational analysis might have a minimal processing overhead

2. Frame Selection Mechanism
- `mpdecimate` uses a comparison algorithm to detect duplicate frames
- It makes decisions about which frames to keep or remove
- While not re-encoding, the frame selection process could potentially introduce very slight
artifacts or discontinuities in frame sequence

Technical Nuance
True quality loss occurs during re-encoding. In this case, with `mpdecimate`,
you're not re-compressing the video, so the original video's visual fidelity remains intact.

- For Clever FFmpeg-GU, reach out to @ProWo for how to use the tool.

If there is no re-encoding, where is "quality loss" came from?

I leaning more to GUI, but not see how to use filters in Clever FFmpeg-GUI

[poisondeathray]

For I-frame only encoded mpeg2 , yes

For you - no, because it's a long gop encode (some frames reference data from adjacent frames). Whenever you interrupt or edit within a GOP, the entire GOP must be re-encoded

Yeah... I guess I remembering those programs that re-encode only split section and direct stream copy the rest. But since splits is every 6 frames - it's not make much sense in here

The GOP length is 15, so you end up re-encoding the entire thing anyways even with a smart renderer

When using the `mpdecimate` filter, there are actually two potential scenarios of "quality" impact:

And for ffmpeg, anything -vf means data gets decoded to uncompressed before the filter chain - so this usually means re-encoding and quality loss, unless you leave it uncompressed (very huge filesizes) , or re-encode with lossless compression (huge filesizes)

[Selur]

Yes, it is possible to remove duplicate frames without re-encoding the video.

Wrong, since the original post implied that the video format does not change.
Also

ffmpeg -i input.dvd.mkv -vf "mpdecimate=max=1:hi=64:lo=64" -vsync passthrough output.mkv

does reencode, independent of the input format of the 'input.dvd.mkv'.

[cinephil]

OK. I got the answer to my question.

Conclusion - I need to find a PAL DVD with the same content

[pandy]

poisondeathray is right and videoAI not - you can only remove losslessly repeated frames (if they are duplicated in MPEG syntax) - for this DGPulldown is probably best tool - if repeated frames are hardcoded then there is no way to remove them from stream without re-encoding.

[videoAI]

ffmpeg-mpdecimate-filter-for-dummies