[haiku-bugs] [Haiku] #11018: [Media Kit]: BMediaFormats::GetFormatFor doesn't find any formats anymore
- From: "colin" <trac@xxxxxxxxxxxx>
- Date: Wed, 09 Jul 2014 14:08:19 -0000
#11018: [Media Kit]: BMediaFormats::GetFormatFor doesn't find any formats
anymore
-------------------------------------------------+-------------------------
Reporter: colin | Owner: axeld
Type: bug | Status: new
Priority: normal | Milestone:
Component: Kits/Media Kit | Unscheduled
Keywords: BMediaFormats, GetFormatFor, DVB, | Version:
ffmpeg | R1/Development
Blocking: | Blocked By:
Platform: All | Has a Patch: 0
-------------------------------------------------+-------------------------
While working on bringing DVB support back to life I encountered a bug
that was introduced by the commits [a] and [b].
The bug hides in the realm of an app requesting a specific decoder (MPEG2
video and MP3 audio in the case of DVB support). When the app requests
these decoders via BMediaFormats::GetFormatFor() (see [c] for a code
snippet in the dvb.media_addon) it won't find any decoders, because the
AddOnManager ([d]) didn't load the ffmpeg media plugin and its codecs yet.
I've commited two unit tests (MPEG2 video decoding [f] and MP3 video
decoding [g]) to the haiku repo, that demonstrate the bug. For example:
Just set a breakpoint at [h] and see that the status returned is not B_OK
as one would expect. When you step in to the call to
formats.GetFormatFor() one line earlier, you will see that there are no
codecs loaded yet.
I tried the following solutions:
1. Load the plugins (_RegisterAddons()) within the constructor of the
AddOnManager.
2. Call AddOnManager::LoadState() (After reintroducing the Method
LoadState() in the AddOnManager) from within the constructor of
BMediaFormats.
Both solutions successfully (as in tried and confirmed) emulate the
behavior of AddOnManager when it was still part of the media_server. Back
then the media_server issued a call to AddOnManager::LoadState() in the
method ReadyToRun() (see [e]) resulting in the loading of all ffmpeg's
codecs.
But both solutions smell bad to me. Unfortunately I can't really tell why
it smells bad to me. As of now I would rather prefer the former way of
handling media plugins via the media_server.
There exists a mailing list discussion thread [i] with Adrien explaining
the reason behind both commits ([a] and [b]) and Axel outlining a possible
solution on the server side.
== References ==
[a] '''Move media plug-in support to application side.''' http://cgit
.haiku-
os.org/haiku/commit/src/kits/media?id=2feaa37f244d707251f7fe1184ce4f7d30251e2d
[b] '''Urpdate AddOnManager and FormatManager for Media Kit.'''
http://cgit.haiku-
os.org/haiku/commit/src/kits/media?id=bf3b475c3838eb2da1f4a97b214535698902380b
[c] '''dvb.media_addon:''' https://github.com/haiku/haiku/blob/master/src
/add-ons/media/media-add-ons/dvb/MediaFormat.cpp#L160
[d] '''Media Kit's AddOnManager:'''
https://github.com/haiku/haiku/blob/master/src/kits/media/AddOnManager.cpp
[e] '''media_server's old code location of loading all ffmpeg codecs:'''
http://cgit.haiku-
os.org/haiku/tree/src/servers/media/media_server.cpp?id=hrev46599#n152
[f] '''mpeg2_decoder_test:''' http://cgit.haiku-
os.org/haiku/tree/src/tests/kits/media/mpeg2_decoder_test?id=hrev47470
[g] '''mp3_decoder_test:''' http://cgit.haiku-
os.org/haiku/tree/src/tests/kits/media/mp3_decoder_test?id=hrev47470
[h] '''breakpoint in unit test mpeg2_decoder_test where the bug shows
itself:''' http://cgit.haiku-
os.org/haiku/tree/src/tests/kits/media/mpeg2_decoder_test/mpeg2_decoder_test.cpp?id=hrev47470#n189
[i] '''mailing list discussion about this bug:'''
//www.freelists.org/post/haiku-development/Media-plugin-support-to-
message-or-not-to-message
--
Ticket URL: <https://dev.haiku-os.org/ticket/11018>
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