Not frame-by-frame render video! (FIXED)

[Pattern]

In the render video frames do not match the original sequence - some are missing, some are doubled.

The sample project is in an attachment.

Compare the original sequence of numbered frames and final video (25fps). 28 frame is missing, but 29 is doubled. Further, the error is repeated periodically, and even growing.

This error occurs on any version of REAPER or FFMPEG encoder. On AMD or INTEL CPU.
On any source video and in/out codec (from youtube, for example).

[Pattern]

Please render source image sequence on your system with 25fps.
What result?

[JamesPeters]

When I render this video project (after unmuting the image track and deleting your rendered video track in the project!), using Reaper 64-bit on Windows 7 64-bit:

At 25 fps as MOV, MKV, MPEG1, MPEG2, FLV, AVI (using different codecs whenever possible for each type such as MPEG2), I get the following results when I play back the file at 10% speed in a player that supports it (I used VLC as well as BS Player):

Number 28 and number 56 are skipped. I actually see number 28 for a fraction of a second (maybe 1/3 second) and then number 29 stays on the screen a slight bit longer to compensate. Likewise when number 56 is skipped, I see number 58 staying onscreen slightly longer to compensate.

When playing at normal speed, this is impossible for me to notice. Even as slow as 50% speed it's impossible to see that a number image is skipped although it does seem as though the progression of images isn't smooth at those points.

I also encoded some files at 24 fps and got "missing numbers" in a different sequence and a bit more frequently (although at that point I figured the test was done and I didn't document what was different).

At 29.97 fps and 30 fps I didn't see any images skipped at all, and I tested with every available codec and filetype. Depending on the file sometimes I'd notice it would seem lagging on every 5th image for a small time (perhaps 1/5 second) which it would catch up on a subsequent image, but overall the progression at normal speed seemed perfectly fine (although at 50% speed it was apparent the images weren't transitioning as smoothly as they could).

I couldn't test this for WEBM since the players I have won't slow the files down that slow, and I don't notice this at normal speed.

This could be a matter of how the codec works at different framerates, or how encoded video works given this sort of source material. It doesn't necessarily mean video with other source material will render with stuttering at 25 fps. Anyway it doesn't seem to be FFMPEG specifically since I used all available codecs and got the same results. I wouldn't immediately blame Reaper though unless you got perfect and repeatable results in another video editor. (I currently have no other video editors installed on my system so I didn't test this.)

As a further test:

I started a new project and set the project settings specifically for 25 fps first, then set the timeline to "frames" and imported your image files and placed them on each frame # (as you did). I got the same results when rendering at 25 fps as before.

[Pattern]

Thank you for such detailed tests!

I was doing about the same thing many times, and at different video source (with different cameras or from the Internet). If the output to 25 frames per second, the error is always present! Other FPS I have not tried.
Apparently the problem is not in the final codec (FFMPEG), but somewhere before, during the formation of the frame flow.

I understand that REAPER is not a professional video editor, but this is an obvious mistake, which even normal demo does not allow. I'm working on music for the animation and this error is very visible in the final video.

Despite the availability of features for working with video in REAPER, i have to use an external encoder in which to mix the audio from REAPER and the original video.

Most likely the error elimination is really very difficult, because watching it for many months and even wrote about it here. As a temporary solution would be great in the video rendering settings to be able to simply replace the audio track in the original video file. To at least do not use external encoder and only use REAPER.

[Justin]

is your project frame rate set to 25fps (in addition to the render frame rate of 25fps)?

[JamesPeters]

Originally Posted by Justin

is your project frame rate set to 25fps (in addition to the render frame rate of 25fps)?

That is correct. After my first tests, I then started a new project set to 25 fps in the project settings (in advance before doing anything), then loaded the 100 image files from his project that I had saved in a folder (recreating his project "from scratch" with the 25 fps project setting just in case).

I also tried the image track with and without the video processor loaded (with a couple different arbitrary settings) just in case. There was no difference in this particular behavior.

[Pattern]

Yes, project frame rate set to 25fps, source video 25fps, render settings 25fps.
In any in/out video format and codec.

The sequence of images with text frame counter i made for clarity.

[Justin]

Thank you! Fixing.

[JamesPeters]

Glad to help, and thanks!

Tested v5.29pre7 (Windows 7 64-bit, Reaper 64-bit, latest 64-bit FFPMEG). Problem resolved. As long as the project framerate is the same as the final encoded file's framerate, and each image is lined up on a frame, there are no skipped images or lags in how they're displayed. Tested at 24 / 25 / 29.97 and 30 fps (first setting the project to the chosen framerate, aligning all images to snap to the frame and resizing as needed, then rendering/encoding at the project's specified framerate). Did this using FFPMEG with rendered files as MKV and MOV, played back at 10% speed using BS Player several times in a row and saw no problems (it also looked smooth at 50% and 100% speeds). I stopped testing after that.

Well actually I tried the project setting at 25 fps (with images snapped to each frame) but then rendering/encoding to 24 fps, and there were a few dropped images like before (every 30 or so, one was skipped). I also tried the project setting at 25 fps (with images snapped to each frame) rendering/encoding at 29.97 and 30 fps, and noticed lags in every "2" and "7" image displayed (every 5 images). But I guess this is normal.

[Pattern]

Wow! Now everything is normal!
I checked all the formats and codecs at 25fps in project settings and render settings.
Source video also 25fps (from camera and youtube).
Thank you Justin for hot fix!
Thanks you James for thorough testing!

There is one more question - a little shifted sound after render with different encoders. See attachment.

It is not very important, because most commonly used AVC (H.264 / AAC). But anyway. And apparently, this shift feature FFMPEG?


P.S. The option in render settings to replace the original audio in a video file without transcoding all the same it would be great to have!