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c76561639d
Original commit message from CVS: * HACKING: Mention ffmpeg snapshot update * ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_codecid_to_caps), (gst_ffmpeg_caps_to_codecid), (gst_ffmpeg_get_codecid_longname): Add new codec types from FFMpeg snapshot update to 2006-02-17 4:00 GMT
259 lines
11 KiB
Text
259 lines
11 KiB
Text
THE GOAL
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--------
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What we are trying to achieve:
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satisfy:
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patching of CVS checkout using our patch files placed in our CVS
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passing of
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make
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make distcheck
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non-srcdir build (ie, mkdir build; cd build; ../configure; make)
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THE SETUP
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---------
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There is a "mirror" root CVS module that contains "ffmpeg".
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This directory contains a vendor-branch checkout of upstream FFmpeg CVS
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of a given day.
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On head, the following things have been commited on top of this:
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* patches/, which is a directory with a set of patches, and a series file
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listing the order, as generated by quilt
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* .pc/, which is a tree of files that quilt uses to keep control of its state.
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It contains a list of applied patches, and one directory per patch,
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containing a tree of hardlinked files that were added to the patchset, and
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a .pc file listing all files part of the patchset.
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* the result of having all these patches commited (ie, quilt push -a) to the
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ffmpeg tree.
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Both the actually patched CVS ffmpeg code as well as the .pc dir need to be
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commited to CVS so the state of quilt wrt. the source is in sync.
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THE WARNING
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-----------
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***
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NEVER EVER commit stuff in gst-libs/ext/ffmpeg UNLESS your quilt stack is
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completely applied !
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This means, ALWAYS make sure quilt push -a has been run without problems.
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What's more, if you want to be on the safe side, make sure that you can
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unapply and reapply without problems, by running quilt pop -a then
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quilt push -a.
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The ONLY exception to this is when you're working on a branch to update
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the upstream source you're working with.
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***
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THE WAY
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-------
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- If you want to hack on our copy of the FFmpeg code, there are some basic
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rules you need to respect:
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- you need to use quilt. If you don't use quilt, you can't hack on it.
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- we separate patches based on the functionality they patch, and whether
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or not we want to send stuff upstream. Make sure you work in the right
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patch. use "quilt applied" to check which patches are applied.
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- before starting to hack, run cvs diff. There should be NO diffs, and
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NO files listed with question mark. If there are, somebody before you
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probably made a mistake. To manage the state correctly, it is vital that
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none of the files are unknown to CVS.
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- if you want to add a file to a patchset, you need to:
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- be in the right patchset
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- quilt add (file)
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- cvs add .pc/(patchsetname)/(file)
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- cvs commit .pc/(patchsetname) (to update the state of quilt in cvs)
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- edit the file
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- cvs add the file if it doesn't exist yet
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- quilt refresh
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- quilt push -a (This one is IMPORTANT, otherwise you'll have a huge diff)
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- cvs commit
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- if you want to add a patchset, you need to:
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- go over the procedure with thomas to check it's correct
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- decide where in the stack to put it. ask for help if you don't know.
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- go there in the patch stack (use quilt pop/push)
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- quilt new (patchsetname).patch (don't forget .patch !)
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- quilt add (files)
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- cvs add .pc/(patchsetname) the whole tree
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- cvs commit .pc/(patchsetname)
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- quilt refresh
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- quilt push -a
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- cvs commit
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- cvs diff (to check if any of the files are unknown to CVS; if they are,
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you need to add them to CVS)
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THE UPSTREAM
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------------
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At some points you want to update the upstream snapshot code to a newer date.
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This is easy if you follow the steps outlined here, but make sure to follow
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them correctly !
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- find a good CVS snapshot date for upstream, one that is known to work.
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You're going to save yourself quite a bit of trouble if you verify this
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first !
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- check it out to a local directory:
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cvs -z9 -d:pserver:anonymous@mplayerhq.hu:/cvsroot/ffmpeg export -D '2004-04-11 23:00 GMT' ffmpeg
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- compile it and test it, make sure it works
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- in gst-ffmpeg/gst-libs/ext/ffmpeg:
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- Pre-flight checks:
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- first make sure you don't have local changes, all files are either in
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CVS or in .cvsignore patch, the whole quilt stack is applied, and stuff
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works.
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- do a quilt pop -a and quilt push -a to verify everything is ok.
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- Branch and rollback:
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- tag HEAD with the branch root point:
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cvs tag BRANCH-UPDATE-CVS-2004-04-11-23-00-ROOT
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- branch:
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cvs tag -b BRANCH-UPDATE-CVS-2004-04-11-23-00
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- FIXME: lock cvs HEAD
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- update local copy to branch:
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cvs update -r BRANCH-UPDATE-CVS-2004-04-11-23-00
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- peel off all patches:
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quilt pop -a
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- commit this
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cvs commit
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- check
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cvs diff
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you should only have ? for files that are generated somehow (binaries,
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build files, ...)
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you get warnings about cvs not finding files to diff that are in .pc
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or generated by your patches
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- if you want, you can now compare this state of CVS (which should
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be last upstream CVS combined with your local unapplied quilt state)
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- remember to NOT do cvs update from here on, since you popped your quilt
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state all your added files that are also in CVS are not locally present.
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- sync with upstream:
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- in a temp dir, redo the export:
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cd ..
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mkdir tmp
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cd tmp
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cvs -z9 -d:pserver:anonymous@mplayerhq.hu:/cvsroot/ffmpeg export -D '2004-04-11 23:00 GMT' ffmpeg
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- rsync it over the old ffmpeg tree
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rsync -arv ffmpeg ..
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- go back and commit this new snapshot
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cd ../ffmpeg
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cvs commit
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- check if any new files got added that you should add to cvs
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cvs diff
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This will list a lot of local files missing, from your quilt state,
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which you shouldn't worry about. Just inspect all the ?'s and add
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files to cvs that belong to upstream and should be in cvs.
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- if everything's ok and commited, tag the state:
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cvs tag UPSTREAM-CVS-2004-04-11-23-00
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- reapply and fix quilt patches one by one
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- try applying one
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quilt push
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- if that didn't work, inspect the patch and figure out how to fix it:
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- if the patch got applied upstream completely, quilt push will tell
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you the patch looks like a reverse patch. In that case you can
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remove the patch from your patches file (patches/series), and
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remove the .pc/$(patchname) and patches/$(patchname).patch files from
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cvs.
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- if the patch conflicts somehow, you can force application with
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quilt push -f
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and then resolve all the rejects, and fix the patch completely.
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Then refresh quilt state with
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quilt refresh
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- when the patch is succesfully removed or reworked, commit current state
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to CVS, then check again if nothing is missing using cvs diff, and
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resolve problems/apply missing files from your quilt state/...
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- after reapplying your complete quilt state, test locally if the complete
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gst-ffmpeg module now works. Compile and test. Resolve all problems
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(upstream errors, missing symbols, missing files, ...) until you have
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a working module. commit again.
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- merge to head:
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- update locally back to head
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cvs update -A
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- FIXME: unlock cvs HEAD
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- merge from your branch
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cvs update -j BRANCH-UPDATE-CVS-2004-04-11-23-00
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- commit
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cvs commit
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- check for diffs
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cvs diff
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- tag merge point
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cvs tag BRANCH-UPDATE-CVS-2004-04-11-23-00-MERGE
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- add upstream date to "THE RECORDS" below
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- get a drink
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THE PLUGIN
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----------
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Some notes on how ffmpeg wrapping inside GStreamer currently works:
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* gstffmpeg{dec,enc,demux,mux}.c are wrappers for specific element types from
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their ffmpeg counterpart. If you want to wrap a new type of element in
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wrapper file.
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The ffmpeg element types, define a whole *list* of elements (in
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GStreamer, each decoder etc. needs to be its own element).
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We use a set of tricks for that to keep coding simple: codec
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mapping and dynamic type creation.
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* ffmpeg uses CODEC_ID_* enumerations for their codecs. GStreamer uses caps,
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which consists of a mimetype and a defined set of properties. In ffmpeg,
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these properties live in a AVCodecContext struct, which contains anything
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that could configure any codec (which makes it rather messy, but ohwell).
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To convert from one to the other, we use codec mapping, which is done in
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gstffmpegcodecmap.[ch]. This is the most important file in the whole
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ffmpeg wrapping process! It contains functions to go from a codec type
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(video or audio - used as the output format for decoding or the input
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format for encoding), a codec id (to identify each format) or a format id
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(a string identifying a file format - usually the file format extension)
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to a GstCaps, and the other way around.
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* to define multiple elements in one source file (which all behave similarly),
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we dynamically create types for each plugin and let all of them operate on
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the same struct (GstFFMpegDec, GstFFMpegEnc, ...). The functions in
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gstffmpeg{dec,enc,demux,mux}.c called gst_ffmpeg*_register() do this.
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The magic is as follows: for each codec or format, ffmpeg has a single
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AVCodec or AV{Input,Output}Format, which are packed together in a list of
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supported codecs/formats. We simply walk through the list, for each of
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those, we check whether gstffmpegcodecmap.c knows about this single one.
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If it does, we get the GstCaps for each pad template that belongs to it,
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and register a type for all of those together. We also leave this inside
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a caching struct, that will later be used by the base_init() function to
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fill in information about this specific codec in the class struct of this
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element (pad templates and codec/format information). Since the actual
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codec information is the only thing that really makes each codec/format
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different (they all behave the same through the ffmpeg API), we don't
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really need to do anything else that is codec-specific, so all other
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functions are rather simple.
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* one particular thing that needs mention is how gstffmpeg{mux,demux}.c and
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gstffmpegprotocol.c interoperate. ffmpeg uses URLProtocols for data input
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and output. Now, of course, we want to use the *GStreamer* way of doing
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input and output (filesrc, ...) rather than the ffmpeg way. Therefore, we
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wrap up a GstPad as a URLProtocol and register this with ffmpeg. This is
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what gstffmpegprotocol.c does. The URL is called gstreamer://%p, where %p
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is the address of a GstPad. gstffmpeg{mux,demux}.c then open a file called
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gstreamer://%p, with %p being their source/sink pad, respectively. This
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way, we use GStreamer for data input/output through the ffmpeg API. It's
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rather ugly, but it has worked quite well so far.
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* there's lots of things that still need doing. See the TODO file for more
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information.
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THE RECORDS
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-----------
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- list of snapshots used:
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CVS-2004-04-11-23-00
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* other updates people didn't enter :)
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CVS-2006-02-17-04-00
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THE REMINDERS
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-------------
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* the initial ffmpeg checkout was imported using:
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- get CVS ffmpeg
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cvs -z3 -d:pserver:anonymous@mplayerhq.hu:/cvsroot/ffmpeg co -D '2004-03-09 06:00 GMT' ffmpeg
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