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I have a few (XviD) videos that I want to play on a standalone DVD player. The thing is that I can’t stand watching videos at normal speed and prefer to watch them sped up some (~1.3x ~ 1.8x).

When watching videos on my computer, I can easily accomplish that by using VLC’s tempo modification controls, but a standalone player does not have them (at least not fine-graind adjustments, not to mention the audio won’t play at non-normal—speed).

I have tried using VirtualDub to adjust the frame-rate, but it doesn’t seem to affect the audio which continues to play at normal speed.

While searching, I found a video on YouTube that looked promising, but it ended up re-encoding the video.

Is there a way to alter the speed of a video without having to re-encode the whole thing?

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> found a video on YouTube that looked promising, but it ended up re-encoding the video. — what exactly did you do there? –  slhck Dec 23 '12 at 20:30
    
what exactly did you do there? @slhck, me? Nothing; I just watched the video. The person ended up re-encoding the video in addition to adjust its speed. –  Synetech Dec 23 '12 at 20:32
    
I just thought "it" was some procedure where it'd be nice to know what exactly was done, but given you've answered this yourself, never mind :) –  slhck Dec 23 '12 at 20:34
    
I thought it was clear that it meant the video, but I see what you mean. –  Synetech Dec 23 '12 at 21:02

1 Answer 1

up vote 1 down vote accepted

Sadly, changing the speed of a video is not as simple as just changing a single number that indicates the framerate. It would be great if the framerate indicated to the player what speed to play back at, but unfortunately that is not how it works because of the nature of the video container. As such, the audio and video are handled separately and need to be adjusted individually.

Fortunately however, you don’t have to re-encode the video, but you will need to re-encode the audio. Here’s how:

  1. Open the video in VirtualDub
  2. Select Video ⇨ Direct stream copy
  3. Select Video ⇨ Frame Rate (figure 1)
  4. Select Change frame rate to (fps) and enter your desired framerate (you can use math to adjust to a percentage based on the original framerate)
  5. Select Audio ⇨ Full processing mode
  6. Check Audio ⇨ Use advanced filtering
  7. Click Audio ⇨ Filters…
  8. Add the following filters in order (figure 2):
    1. input
    2. time stretch
    3. output
  9. Double-click the time stretch filter
  10. Enter a new ration based on the modification to the framerate (e.g., 30fps ⇨ 60fps means a ratio of 0.5)
    • You can click the Test button in the Audio filters dialog to make sure you set the ratio in the correct direction
  11. Click OK

    (Now for the unpleasant part.)

  12. Click Audio ⇨ Compression…

  13. Select a compressor (the same one as the original audio stream if possible)
  14. Select an appropriate format (you can find out what format the original is via File ⇨ File Information…)
  15. Save your video

When the video is saved, the video will not be re-encoded (you used Direct stream copy, but the audio will be. If audio quality is an issue (i.e., quality loss due to re-compressing), then you may want to use a slightly higher format. If audio quality is not a concern, then this should be sufficient. It will not take anywhere near as long as using another program to fully re-encode the whole thing because the video would take the most time, but re-encoding the audio only takes about as long as making an MP3.


Figure 1: Changing the framerate

VDub framerate


Figure 2: Changing the audio rate

VDub audio rate

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Small changes in frame rate might be acceptable, but even then it depends a lot on the GOP structure/number of I-frames. Increasing the video frame rate will simply duplicate certain frames, whereas decreasing the rate will mess with the key frames/GOPs and delete some of them, so overdoing it will make the video jerky. Frame rate conversion (for example NTSC to to PAL or vice versa) is not so simple to do and YMMV a lot depending on the source and amount of rate adjustment required. –  Karan Dec 23 '12 at 20:43
    
I don’t know about format conversion since I only use NTSC, but I’ve tried it with 2x and it was fine. In my case, these are throw-away videos that I want to watch on TV instead of having to use a computer, but don’t want to waste time. If I were going to archive them permanently, I would leave them as-is. –  Synetech Dec 23 '12 at 21:01

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