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116 lines
5.4 KiB
116 lines
5.4 KiB
CONTEXT |
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======= |
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The FFmpeg project merges all the changes from the Libav project |
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(https://libav.org) since the origin of the fork (around 2011). |
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With the exceptions of some commits due to technical/political disagreements or |
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issues, the changes are merged on a more or less regular schedule (daily for |
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years thanks to Michael, but more sparse nowadays). |
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WHY |
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=== |
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The majority of the active developers believe the project needs to keep this |
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policy for various reasons. |
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The most important one is that we don't want our users to have to choose |
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between two distributors of libraries of the exact same name in order to have a |
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different set of features and bugfixes. By taking the responsibility of |
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unifying the two codebases, we allow users to benefit from the changes from the |
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two teams. |
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Today, FFmpeg has a much larger user database (we are distributed by every |
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major distribution), so we consider this mission a priority. |
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A different approach to the merge could have been to pick the changes we are |
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interested in and drop most of the cosmetics and other less important changes. |
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Unfortunately, this makes the following picks much harder, especially since the |
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Libav project is involved in various deep API changes. As a result, we decide |
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to virtually take everything done there. |
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Any Libav developer is of course welcome anytime to contribute directly to the |
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FFmpeg tree. Of course, we fully understand and are forced to accept that very |
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few Libav developers are interested in doing so, but we still want to recognize |
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their work. This leads us to create merge commits for every single one from |
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Libav. The original commit appears totally unchanged with full authorship in |
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our history (and the conflict are solved in the merge one). That way, not a |
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single thing from Libav will be lost in the future in case some reunification |
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happens, or that project disappears one way or another. |
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DOWNSIDES |
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========= |
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Of course, there are many downsides to this approach. |
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- It causes a non negligible merge commits pollution. We make sure there are |
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not several level of merges entangled (we do a 1:1 merge/commit), but it's |
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still a non-linear history. |
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- Many duplicated work. For instance, we added libavresample in our tree to |
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keep compatibility with Libav when our libswresample was already covering the |
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exact same purpose. The same thing happened for various elements such as the |
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ProRes support (but differences in features, bugs, licenses, ...). There are |
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many work to do to unify them, and any help is very much welcome. |
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- So much manpower from both FFmpeg and Libav is lost because of this mess. We |
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know it, and we don't know how to fix it. It takes incredible time to do |
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these merges, so we have even less time to work on things we personally care |
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about. The bad vibes also do not help with keeping our developers motivated. |
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- There is a growing technical risk factor with the merges due to the codebase |
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differing more and more. |
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MERGE GUIDELINES |
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================ |
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The following gives developer guidelines on how to proceed when merging Libav commits. |
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Before starting, you can reduce the risk of errors on merge conflicts by using |
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a different merge conflict style: |
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$ git config --global merge.conflictstyle diff3 |
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tools/libav-merge-next-commit is a script to help merging the next commit in |
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the queue. It assumes a remote named libav. It has two modes: merge, and noop. |
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The noop mode creates a merge with no change to the HEAD. You can pass a hash |
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as extra argument to reference a justification (it is common that we already |
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have the change done in FFmpeg). |
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Also see tools/murge, you can copy and paste a 3 way conflict into its stdin |
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and it will display colored diffs. Any arguments to murge (like ones to suppress |
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whitespace differences) are passed into colordiff. |
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TODO/FIXME/UNMERGED |
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=================== |
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Stuff that didn't reach the codebase: |
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------------------------------------- |
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- HEVC DSP and x86 MC SIMD improvements from Libav (see https://ffmpeg.org/pipermail/ffmpeg-devel/2015-December/184777.html) |
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- 1f821750f hevcdsp: split the qpel functions by width instead of by the subpixel fraction |
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- 818bfe7f0 hevcdsp: split the epel functions by width |
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- 688417399 hevcdsp: split the pred functions by width |
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- a853388d2 hevc: change the stride of the MC buffer to be in bytes instead of elements |
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- 0cef06df0 checkasm: add HEVC MC tests |
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- e7078e842 hevcdsp: add x86 SIMD for MC |
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- 7993ec19a hevc: Add hevc_get_pixel_4/8/12/16/24/32/48/64 |
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- new bitstream reader (see http://ffmpeg.org/pipermail/ffmpeg-devel/2017-April/209609.html) |
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- use av_cpu_max_align() instead of hardcoding alignment requirements (see https://ffmpeg.org/pipermail/ffmpeg-devel/2017-September/215834.html) |
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- f44ec22e0 lavc: use av_cpu_max_align() instead of hardcoding alignment requirements |
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- 4de220d2e frame: allow align=0 (meaning automatic) for av_frame_get_buffer() |
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- Support recovery from an already present HLS playlist (see 16cb06bb30) |
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- Remove all output devices (see 8e7e042d41, 8d3db95f20, 6ce13070bd, d46cd24986 and https://ffmpeg.org/pipermail/ffmpeg-devel/2017-September/216904.html) |
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Collateral damage that needs work locally: |
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------------------------------------------ |
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- Merge proresdec2.c and proresdec_lgpl.c |
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- Merge proresenc_anatoliy.c and proresenc_kostya.c |
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- Fix MIPS AC3 downmix |
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Extra changes needed to be aligned with Libav: |
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---------------------------------------------- |
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- Switching our examples to the new encode/decode API (see 67d28f4a0f) |
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- HEVC IDCT bit depth 12-bit support (Libav added 8 and 10 but doesn't have 12)
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