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d20df2601f
For reasons we are not privy to, nvidia decided that the nvenc encoder should apply aspect ratio compensation to 'DVD like' content, assuming that the content is not bt.601 compliant, but needs to be bt.601 compliant. In this context, that means that they make the following, questionable, assumptions: 1) If the input dimensions are 720x480 or 720x576, assume the content has an active area of 704x480 or 704x576. 2) Assume that whatever the input sample aspect ratio is, it does not account for the difference between 'physical' and 'active' dimensions. From, these assumptions, they then conclude that they can 'help', by adjusting the sample aspect ratio by a factor of 45/44. And indeed, if you wanted to display only the 704 wide active area with the same aspect ratio as the full 720 wide image - this would be the correct adjustment factor, but what if you don't? And more importantly, what if you're used to ffmpeg not making this kind of adjustment at encode time - because none of the other encoders do this! And, what if you had already accounted for bt.601 and your input had the correct attributes? Well, it's going to apply the compensation anyway! So, if you take some content, and feed it through nvenc repeatedly, it will keep scaling the aspect ratio every time, stretching your video out more and more and more. So, clearly, regardless of whether you want to apply bt.601 aspect ratio adjustments or not, this is not the way to do it. With any other ffmpeg encoder, you would do it as part of defining your input paramters or do the adjustment at playback time, and there's no reason by nvenc should be any different. This change adds some logic to undo the compensation that nvenc would otherwise do. nvidia engineers have told us that they will work to make this compensation mechanism optional in a future release of the nvenc SDK. At that point, we can adapt accordingly. Signed-off-by: Philip Langdale <philipl@overt.org> Reviewed-by: Timo Rothenpieler <timo@rothenpieler.org> Signed-off-by: Michael Niedermayer <michaelni@gmx.at> |
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|---|---|---|
| compat | ||
| doc | ||
| libavcodec | ||
| libavdevice | ||
| libavfilter | ||
| libavformat | ||
| libavresample | ||
| libavutil | ||
| libpostproc | ||
| libswresample | ||
| libswscale | ||
| presets | ||
| tests | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| arch.mak | ||
| Changelog | ||
| cmdutils_common_opts.h | ||
| cmdutils_opencl.c | ||
| cmdutils.c | ||
| cmdutils.h | ||
| common.mak | ||
| configure | ||
| COPYING.GPLv2 | ||
| COPYING.GPLv3 | ||
| COPYING.LGPLv2.1 | ||
| COPYING.LGPLv3 | ||
| CREDITS | ||
| ffmpeg_dxva2.c | ||
| ffmpeg_filter.c | ||
| ffmpeg_opt.c | ||
| ffmpeg_vda.c | ||
| ffmpeg_vdpau.c | ||
| ffmpeg.c | ||
| ffmpeg.h | ||
| ffplay.c | ||
| ffprobe.c | ||
| ffserver_config.c | ||
| ffserver_config.h | ||
| ffserver.c | ||
| INSTALL.md | ||
| library.mak | ||
| LICENSE.md | ||
| MAINTAINERS | ||
| Makefile | ||
| README.md | ||
| RELEASE | ||
| RELEASE_NOTES | ||
| version.sh | ||
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 analisys tool to inspect multimedia content.
- 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.