Modifying speed without Altering Pitch

[Djard007]

Modifying video speed (frame rate) in X9 without altering audio pitch is possible with the Speed/Time-lapse feature, but the process damages the audio with loss of quality, which is unacceptable to a discerning musician. Below is a workaround that appears arduous, but it takes longer to read the instructions than to perform them. If there is a better way, or a way to truncate the process, please share.

In the following example, we will split a clip into four parts: A, B, C and D. We will speed up part B to 150%, and speed up part C to 200%, preserving the audio quality.


SPLIT CLIP INTO PARTS

1. Open video in "Edit" work space.
2. Drag scrubber to start point of section you wish to speed up (start of part B)
-> Split clip (scissors icon under preview window) -> make a note of the point:
e.g. 24.00 secs or use a description of the video frame.
3. Drag scrubber to point from where you want to end 150% speed, (and begin
200% speed, part C) -> Split clip (scissors) -> make a note of the point.
4. Split clip where you want to end 200% speed -> make a note of this point,
where part C ends and part D starts.
5. Right-click on any part of video -> Properties -> make a note of the clip
(entire) duration -> play each segment. Approximate duration will appear at
lower right of preview window. For example...

Part A: 00.00 -> 19.13 sec.
Part B: 19.14 -> 25.20 "
Part C: 25.21 -> 31.05 "
Part D: 31.06 -> 42.10 "

NOTE: VS "Properties" shows 42.417 secs, while Audacity shows 42.428 secs, VD
shows 41.667 secs, and MediaInfo shows 42.371 secs.


SAVE UNEDITED AUDIO PARTS

6. Right-click on part D -> Delete -> also delete parts C and B.

TIP: Storyboard view (icon at far mid left) may simplify location of the parts.

7. Share tab -> Audio -> from "Format" drop-down menu, select WAV -> name
file as "Part A" -> choose destination folder -> Start -> OK.

NOTE: Do NOT alter name of file after rendering.

8. Edit tab -> Edit (upper text menu) -> Undo -> delete part A.
9. Share tab -> repeat steps to render Parts B, C and D. You will then have four
audio files that will be edited and concatenated later when remuxing.


SPEED UP CLIP PARTS B & C

10. Edit tab -> Undo, until all four parts appear in timeline.
11. Right-click on Part B -> Speed/Time-lapse -> set to 150% -> OK.
12. Right-click on Part C -> Speed/Time-lapse -> set to 200% -> OK.


RENDER EDITED CLIP

13. Share tab -> select format (e.g. MP4) -> name file as, say, "Clip
(edited).mp4" -> select destination folder -> Start -> OK -> play the file to
audit your work.


SAVE EDITED AUDIO PARTS B & C

14. Edit tab -> Edit -> Undo (to recover Part B that plays at 150%). Make
sure only part B appears in timeline.
15. Share tab -> Audio -> save as WAV file -> name file as "Part B (edited)"
-> Start -> OK.
16. Edit tab -> undo again to recover parts -> repeats steps to save part C.
You will then have the two sped up files to serve as guides for editing "Part
B.wav" and "Part C.wav" in Audacity.


SYNC AUDIO PARTS B & C

15. Drop "Part B (edited).wav" into Audacity -> drop "Part B.wav" into
Audacity. The two files will appear in separate tracks. Zoom in and make
sure "Part B (edited)" starts at same time as "Part B."
16. Select "Part B.wav" -> Effect -> Sliding Time Scale/Pitch Shift -> start
with the following settings for the 150%...

Initial Tempo Change: 50% Final Tempo Change: 50%

NOTE: You may need to set initial to 49% and Final to 50%.

17. OK -> undo adjustment is necessary -> edit sections to sync if necessary.

NOTE: A minor rise in pitch may also be required.

18. Select only "Part B" track -> File -> Export Selected Audio -> name as, say,
"Part B (synced).wav" -> from "Save as type" drop-down menu, choose "WAV
(Microsoft) signed 16-bit PCM" -> choose destination folder -> Save -> OK ->
OK (skip "Edit Metadata").
19. Delete tracks in Audacity -> repeat steps to sync "Part C.wav," starting
with the following settings for the 200%...

Initial Tempo Change: 100%
Final Tempo Change: 100%

20. Select synced track -> export, naming the file as "Part C (synced).wav."
21. Delete "Part C (edited)" track.


CONCATENATE AUDIO

21. Drop the edited video clip into Audacity that will automatically demux the
audio, which we will use as template for syncing the four audio parts.
22. Drop "part A," "Part B (synced)," "Part C (synced)" and "Part D" into
Audacity. Each part will automatically appear as a separate track.
23. Zoom in -> make sure waveform in "Track A" starts at same time as start
of template.
24. Click in left panel of track with "Part B (synced)" -> Cut -> click just after
end of track with "Part A" -> Paste.
25. Time Shift Tool ("<-->" icon) -> drag "Part B (synced)" leftward, until
yellow vertical line appears, to close the space between the two parts.
26. Delete the now empty "Part B (synced)" track.

TIP: Audit (play) section where the two parts join. Make sure no unwanted
noise was created. If any artifact is discernible, zoom in -> cut a fraction of
the wave in, so that they join on the Y-axis. Do not cut the template track
above that is the duration of the video -> use "Sliding Time Scale/Pitch
Shift" tool to stretch part of the wave, so that the "Part B (synced)" that you
pasted is synchronized with your template above. Set "Initial Tempo Change"
to 0% and "Finale Tempo Change" to whatever (negative) number
synchronizes the tracks--e.g. -17%).

27. Selection Tool -> zoom out -> repeat steps to add remaining parts into
the track below template.
28. Zoom in -> scroll through the tracks and look for any sections of the
wave that do not align -> use the "Sliding Time Scale/Pitch Shift" tool
to sync the waveforms. Anything less than 10 ms is tolerable to even the
most critical ear.

TIP: At this point, you may want to adjust the volume, add EQ or some
effect.

29. Select the concatenated track -> Export Selected Audio -> name the
file as, say, "All Parts Synced.wav" -> Save (as WAV file).


MUX EDITED VIDEO & CONCATENATED AUDIO

30. Drop "Clip (edited).mp4" into AVIdemux GUI -> Audio (upper text menu)
-> Select Track.
31. From "Track 1" drop-down menu, select "Add audio track" -> browse to
and double-click on "All Parts Synced.wav" -> OK.
32. Set as follows for lossless muxing...

Video Output: Copy
Audio Output: AAC (lav)
Output Format: MP4 Muxer

33. MP4 containers support only AAC, MP3 and AC3; so click on "Configure"
-> set audio bitrate to at least the bitrate of the original audio -> OK.

NOTE: Use freeware MediaInfo to determine original bitrate, right-clicking
on original video clip and selecting "MediInfo" from the context menu ->
scroll down to audio section.

NOTE: The current version of AVIdemux offers the highly compressing but
lossless HEVC (x265) codec for a much smaller file.

34. File -> Save -> select destination folder -> name file as, say, "Clip
(finished).mp4" -> Save -> OK -> OK.
35. Play the finished file -> if satisfied, delete the Audacity project.
36. Dance around the room!

[asik1]

Thank you very much for taking the time to type the lost chapter of the bible
This will be very handy for the 1% who needs it.

[Djard007]

That many!!?

I imagine some recording artists might want to take advantage of modern technology. But you are prolly correct. Sigh! I wish there were a more expedient way to manipulate audio in video.

[aljimenez]

Thanks for taking the time to write the process and sharing it with us. Why do you want to speed up portions of a concert? I could see reasons for slowing down, but not for speeding up. Instead of speeding up, why not cut with some smooth transitions?

[Djard007]

Many concert and recording musicians are thrilled to be afforded an opportunity to play a challenging part slowly then speed the part up to normal tempo in the mix. This kind of engineering saves time, not requiring lengthy practice in the studio to play the part masterfully.

It is not unusual for a producer to book a recording artist to the studio before he or she has mastered a piece of music.

I managed a workaround also for preserving audio quality when using the Variable Speed feature in VS, which requires more skill in synchronizing audio with the edited video. I'll be happy to share the steps.

[aljimenez]

Thanks for the explanation. If you have the time, I think it would be helpful for others in the future to read your experiences. Thus I encourage you to post the steps.

[Djard007]

Sure, I'll be happy to share the steps for synchronizing audio after using the useful Variable Speed feature in VS, and will do so after a final edit to truncate the lengthy steps. Am I permitted to include a link to my online Audacity guide, so that I don't need to go into detail about scaling time in the audio track?

[aljimenez]

I think links are allowed.