Novacut 15.08

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Jason Gerard DeRose
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Release notes 

Novacut 15.08 switches to a new rendering backend!

The new rendering backend decouples the problem in to into decoding and encoding, using the GStreamer appsink (decoding) and appsrc (encoding) elements to bridge the two and our own code in between.

Note that the new rendering backend does strict checks to ensure that each input video is conformant enough to meet its expectations, and it will fail with an error if it determines that a correct render cannot be produced.

So some edits that would previously render may now fail with an error. On the balance, this is a good thing because it means we weren't upholding our social contract for frame-accuracy, and these outright failures put pressure on us to fix things correctly (and there is a plan for this: non-destructively conforming a video by building a frame-to-nanosecond index for input videos with malformed timestamps).

However, our general experience thus far through extensive testing is that many edits that would previously fail to render at all, or edits that would produce inaccurate renders, will now produce a perfectly frame-accurate render. But your millage will vary based on how conformant your input videos are.

If you encounter any problems with the new rendering backend, please file a bug!

Important known issues with the new rendering backend:

  1) When using GStreamer 1.2 (Ubuntu 14.04/Trusty), edits that contain a slice that ends at or past two frames from the end of a clip will very likely fail because the last few frames will not be produced, a scenario under which the new renderer will fail with an error; as a work-around, you can adjust the outpoint (slice-stop) to be several frames *before* the end of the clip; details[*] on the underlying problem are at the end of these release notes.

  2) Similar to above, when using GStreamer 1.2 (Ubunut 14.04/Trusty), the thumbnailer will still fail to create a thumbnail for the last few frames in a clip, and the same workaround applies (adjust the outpoint/slice-stop to be several frames before the end of the clip); again, please see the details[*] at the end of these release notes.

  3) When using GStreamer 1.5 (Ubuntu 15.10/Wily), the default encoding setting (which you currently can't edit through the UI), will eat/drop the first two frames of your rendered video (seemingly this is a problem with libx264-146 or with the GSreamer 1.5 x264enc element)

  4) As in the last several Novacut releases, audio rendering is still disabled till we get the design right; apologies!

Other changes in Novacut 15.08 include:

* Add a new `novacut-video-checker` script which can be used to determine whether a video is conformant enough to (likely) be editable with Novacut; example usage:

    $ novacut-video-checker My-Video.MOV

  For details on its complete options, please run:

    $ novacut-video-checker -h

* Fix a bug that totally broke the thumbnailer with GStreamer >= 1.4 (Ubuntu 15.04/Vivid, Ubuntu 15.10/Wily)

* Restore the previous logging behavior: novacut-service now again logs to ~/.cache/novacut/novacut-service.log, and novacut-renderer now again logs to ~/.cache/novacut/novacut-renderer.log

* `./ test` now does static analysis with Pyflakes, which is likewise run during the Debian/Ubuntu package builds (see debian/rules)

* The unit tests are now installed with the `novacut` package; you can run these tests against the installed package like this:

    $ python3 -m

Thanks for watching! :D

[*] Details on issues effecting GStreamer 1.2 (Ubuntu 14.04/Trusty): the problem is that the input decoding pipline will received an EOS event several frames before the end of a clip, meaning that not all the frames can be produced; the old rendering backend would silently ignore this problem, resulting in inaccurate or broken renders, whereas the new rendering backend will fail with an error; note that this problem does not exist with GStreamer 1.4 (Ubuntu 15.04/Vivid) nor with GStreamer 1.5 (Ubuntu 15.10/Vivid).


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