This was the first Google Summer of Code (GSoC) for the GPAC team. GSoC is a program organized by Google “Google Summer of Code (GSoC) is an online, international program designed to encourage university student participation in open source software development”.
Continue reading GPAC report from GSoC 2016
There is often a lot of confusion from people using MP4Box to create MP4 files or DASH content with a specific aspect ratio. This confusion often comes from badly-chosen acronyms in the MP4/DASH standards. In this post, we clarify what MP4Box uses and does. Continue reading Aspect Ratios
Release of GPAC 0.6.0.
Release notes are available at: https://github.com/gpac/gpac/releases/tag/v0.6.0
Bug tracker at: https://github.com/gpac/gpac/issues
Enjoy and spread the news!
Dear adaptive streaming followers,
Many of you reported issues when packaging your encoded content to respectively HLS or MPEG-DASH using GPAC (resp. the MP42TS and MP4Box tools). Most of the time, this is due to misalignment of key-frames across the different encoded qualities. In this article, we are going to show how to check key-frame alignment.
Continue reading Check key-frame alignment with MP4Box
In a previous post we mentionned that we had created an official account on GitHub but at that time the migration was not complete. We still used internally the SVN repository hosted on SourceForge and in particular for our BuildBot to generate the Nightly Builds. The git repository was synced with the SVN repository.
Since last week, we have migrated all our tools to use the git repository hosted on GitHub as the official source code of GPAC. The SVN repository at SourceForge will not be maintained anymore. In fact, recent commits have already been made to GitHub which are not present on the SVN.
As part of that migration, we have changed the numbering of GPAC’s binaries. New builds now use a numbering in the form of 0.5.2-DEV-<number-of-commits-since-last-release>-<latest-git-commit-hash>-<git-branch>.
Note also that GPAC is now also automatically built on TravisCI when a commit is pushed to the repository or when a pull request is made. We hope this move to git and GitHub will help improving the code. So don’t hesitate to fork, fix and make pull requests.
The GPAC team.
We’ve recently improved the language tagging in GPAC, and in particular in MP4Box and in MP4Client. This posts gives details about how to use these new features. Continue reading Improved language tagging in GPAC
This post is the first post in a series I’m writing to help you discover the many different ways to handle tracks in MP4 files using MP4Box and other GPAC tools, with a particular focus on three types of tracks: subtitles, metadata and graphics tracks. Let me start in this post with subtitle tracks. Continue reading Subtitling with GPAC
Following Cyril Concolato’s first attempt to store TTML in ISOBMF, I have added support for parsing and DASHing EBU-TTD as of version 5366 of GPAC. Therefore you don’t need NHML anymore when importing EBU-TTD TTML content. Please read Cyril’s blog post if you wish to know more about TTML or MPEG-4 part 30 (TTML and WebVTT in ISOBMF).
EBU released two specifications recently:
- TECH 3380 v1.0: EBU-TT-D SUBTITLING DISTRIBUTION FORMAT.
This document aims to define a distribution subtitling format base on TTML. This is both a restriction (i.e. a profile) and an extension of TTML. The extensions are very limited. The restrictions allow to mitigate most of the TTML criticisms (especially an ability to express things in several ways, which led to a difficult generic parsing process).
- TECH 3381 v0.9: CARRIAGE OF EBU-TT-D IN ISOBMFF.
This document explains how to store some EBU-TTD content in ISOBMF. Basically it follows the MPEG-4 part 30 standard.
Useful command-lines for import:
MP4Box -add sample.ttml sample.mp4
EBU-TTD is recognized automatically:
MP4Box -add ebu-ttd_sample.xml:ext=ttml -new tmp.mp4
TTML Import Note: TTML import - EBU-TTD detected
To extract the TTML samples from the MP4 (generates one TTML per MP4 sample) (note: replace track 1 from this example with your track id) :
MP4Box -raws 1 sample.mp4
Just a few remarks about this implementation:
- It is made on top of TTML existing support. So it has the same limitations (no images support, etc.).
- DASH segmentation is fully supported.
- Regression tests are still unsufficient. We are looking for additional feedback and test files.
- There are still a few open questions which are on their way to standardization. You can expect a few minor improvements in the future.
EBU-TTD current limitations
/!\ These limitations don’t exist if you use NHML /!\
- Overlapping times are not supported.
- Multiple <region> elements may trigger errors.
/!\ Fixed limitations /\
- The expected default namespace of the EBU-TT-D document is ‘http://www.w3.org/ns/ttml’. Documents where this namespace is bound to prefix are supported starting at 08/30/2015 (but no other namespace checks are performed).
This development has been made possible thanks to EBU through GPAC Licensing.
GPAC people are attending FOSDEM this year. FOSDEM is a conference which allows “open source communities a place to meet, share ideas and collaborate”. It takes place in Brussels, Belgium.
If you’re interested and have questions, meet us or ask questions on our forums.