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Original mail and my own followup on ffmpeg-user earlier today: I have a device sending out a MJPEG/RTP stream on a low quality setting. Decoding and displaying the video with libavformat results in a washed out, low contrast, greyish image. Playing the same stream with VLC results in proper color representation. Screenshots for comparison: http://zevv.nl/div/libav/shot-ffplay.jpg http://zevv.nl/div/libav/shot-vlc.jpg A pcap capture of a few seconds of video and SDP file for playing the stream are available at http://zevv.nl/div/libav/mjpeg.pcap http://zevv.nl/div/libav/mjpeg.sdp I believe the problem might be in the calculation of the quantization tables in the function create_default_qtables(), the attached patch solves the issue for me. The problem is that the argument 'q' is of the type uint8_t. According to the JPEG standard, if 1 <= q <= 50, the scale factor 'S' should be 5000 / Q. Because the create_default_qtables() reuses the variable 'q' to store the result of this calculation, for small values of q < 19, q wil subsequently overflow and give wrong results in the calculated quantization tables. The patch below uses a new variable 'S' (same name as in RFC2435) with the proper range to store the result of the division. Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
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. Few developers
follow pull requests so they will likely be ignored.