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Subject: [media] DocBook: media: update codec section, drop obsolete 'suspended' state Author: Hans Verkuil <hverk...@xs4all.nl> Date: Tue May 7 08:06:11 2013 -0300 The Codec section in the V4L2 specification was marked as 'suspended', even though codec support has been around for quite some time. Update this section, explaining a bit about memory-to-memory devices and pointing to the MPEG controls section. Signed-off-by: Hans Verkuil <hans.verk...@cisco.com> Acked-by: Kamil Debski <k.deb...@samsung.com> Signed-off-by: Mauro Carvalho Chehab <mche...@redhat.com> Documentation/DocBook/media/v4l/dev-codec.xml | 35 +++++++++++++++--------- 1 files changed, 22 insertions(+), 13 deletions(-) --- http://git.linuxtv.org/media_tree.git?a=commitdiff;h=6e7df1cd373d688486b0b0b6626cb32f59ebdcfa diff --git a/Documentation/DocBook/media/v4l/dev-codec.xml b/Documentation/DocBook/media/v4l/dev-codec.xml index dca0ecd..ff44c16 100644 --- a/Documentation/DocBook/media/v4l/dev-codec.xml +++ b/Documentation/DocBook/media/v4l/dev-codec.xml @@ -1,18 +1,27 @@ <title>Codec Interface</title> - <note> - <title>Suspended</title> + <para>A V4L2 codec can compress, decompress, transform, or otherwise +convert video data from one format into another format, in memory. Typically +such devices are memory-to-memory devices (i.e. devices with the +<constant>V4L2_CAP_VIDEO_M2M</constant> or <constant>V4L2_CAP_VIDEO_M2M_MPLANE</constant> +capability set). +</para> - <para>This interface has been be suspended from the V4L2 API -implemented in Linux 2.6 until we have more experience with codec -device interfaces.</para> - </note> + <para>A memory-to-memory video node acts just like a normal video node, but it +supports both output (sending frames from memory to the codec hardware) and +capture (receiving the processed frames from the codec hardware into memory) +stream I/O. An application will have to setup the stream +I/O for both sides and finally call &VIDIOC-STREAMON; for both capture and output +to start the codec.</para> - <para>A V4L2 codec can compress, decompress, transform, or otherwise -convert video data from one format into another format, in memory. -Applications send data to be converted to the driver through a -&func-write; call, and receive the converted data through a -&func-read; call. For efficiency a driver may also support streaming -I/O.</para> + <para>Video compression codecs use the MPEG controls to setup their codec parameters +(note that the MPEG controls actually support many more codecs than just MPEG). +See <xref linkend="mpeg-controls"></xref>.</para> - <para>[to do]</para> + <para>Memory-to-memory devices can often be used as a shared resource: you can +open the video node multiple times, each application setting up their own codec properties +that are local to the file handle, and each can use it independently from the others. +The driver will arbitrate access to the codec and reprogram it whenever another file +handler gets access. This is different from the usual video node behavior where the video properties +are global to the device (i.e. changing something through one file handle is visible +through another file handle).</para> _______________________________________________ linuxtv-commits mailing list linuxtv-commits@linuxtv.org http://www.linuxtv.org/cgi-bin/mailman/listinfo/linuxtv-commits
