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Variables pertaining to the main video are now available when using the scale2ref filter. This allows, as an example, scaling a video with another as a reference point while maintaining the original aspect ratio of the primary/non-reference video. Consider the following graph: scale2ref=iw/6:-1 [main][ref] This will scale [main] to 1/6 the width of [ref] while maintaining the aspect ratio. This works well when the AR of [ref] is equal to the AR of [main] only. What the above filter really does is maintain the AR of [ref] when scaling [main]. So in all non-same-AR situations [main] will appear stretched or compressed to conform to the same AR of the reference video. Without doing this calculation externally there is no way to scale in reference to another input while maintaining AR in libavfilter. To make this possible, we introduce eight new constants to be used in the w and h expressions only in the scale2ref filter: * main_w/main_h: width/height of the main input video * main_a: aspect ratio of the main input video * main_sar: sample aspect ratio of the main input video * main_dar: display aspect ratio of the main input video * main_hsub/main_vsub: horiz/vert chroma subsample vals of main * mdar: a shorthand alias of main_dar Of course, not all of these constants are needed for maintaining the AR, but adding additional constants in line of what is available for in/out allows for other scaling possibilities I have not imagined. So to now scale a video to 1/6 the size of another video using the width and maintaining its own aspect ratio you can do this: scale2ref=iw/6:ow/mdar [main][ref] This is ideal for picture-in-picture configurations where you could have a square or 4:3 video overlaid on a corner of a larger 16:9 feed all while keeping the scaled video in the corner at its correct aspect ratio and always the same size relative to the larger video. I've tried to re-use as much code as possible. I could not find a way to avoid duplication of the var_names array. It must now be kept in sync with the other (the normal one and the scale2ref one) for everything to work which does not seem ideal. For every new variable introduced/removed into/from the normal scale filter one must be added/removed to/from the scale2ref version. Suggestions on how to avoid var_names duplication are welcome. var_values has been increased to always be large enough for the additional scale2ref variables. I do not forsee this being a problem as the names variable will always be the correct size. From my understanding of av_expr_parse_and_eval it will stop processing variables when it runs out of names even though there may be additional (potentially uninitialized) entries in the values array. The ideal solution here would be using a variable-length array but that is unsupported in C90. This patch does not remove any functionality and is strictly a feature patch. There are no API changes. Behavior does not change for any previously valid inputs. The applicable documentation has also been updated. Signed-off-by: Kevin Mark <kmark937@gmail.com> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> |
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| compat | ||
| doc | ||
| ffbuild | ||
| libavcodec | ||
| libavdevice | ||
| libavfilter | ||
| libavformat | ||
| libavresample | ||
| libavutil | ||
| libpostproc | ||
| libswresample | ||
| libswscale | ||
| presets | ||
| tests | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| .travis.yml | ||
| Changelog | ||
| cmdutils_opencl.c | ||
| cmdutils.c | ||
| cmdutils.h | ||
| configure | ||
| CONTRIBUTING.md | ||
| COPYING.GPLv2 | ||
| COPYING.GPLv3 | ||
| COPYING.LGPLv2.1 | ||
| COPYING.LGPLv3 | ||
| CREDITS | ||
| ffmpeg_cuvid.c | ||
| ffmpeg_dxva2.c | ||
| ffmpeg_filter.c | ||
| ffmpeg_opt.c | ||
| ffmpeg_qsv.c | ||
| ffmpeg_vaapi.c | ||
| ffmpeg_vdpau.c | ||
| ffmpeg_videotoolbox.c | ||
| ffmpeg.c | ||
| ffmpeg.h | ||
| ffplay.c | ||
| ffprobe.c | ||
| ffserver_config.c | ||
| ffserver_config.h | ||
| ffserver.c | ||
| INSTALL.md | ||
| LICENSE.md | ||
| MAINTAINERS | ||
| Makefile | ||
| README.md | ||
| RELEASE | ||
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides a mean to alter decoded Audio and Video through chain of filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements color conversion and scaling routines.
Tools
- ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
- ffplay is a minimalistic multimedia player.
- ffprobe is a simple analysis tool to inspect multimedia content.
- ffserver is a multimedia streaming server for live broadcasts.
- Additional small tools such as
aviocat,ismindexandqt-faststart.
Documentation
The offline documentation is available in the doc/ directory.
The online documentation is available in the main website and in the wiki.
Examples
Coding examples are available in the doc/examples directory.
License
FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.
Contributing
Patches should be submitted to the ffmpeg-devel mailing list using
git format-patch or git send-email. Github pull requests should be
avoided because they are not part of our review process and will be ignored.