diff options
Diffstat (limited to 'DOCS')
| -rw-r--r-- | DOCS/tech/libao2.txt | 79 |
1 files changed, 19 insertions, 60 deletions
diff --git a/DOCS/tech/libao2.txt b/DOCS/tech/libao2.txt index e9034ae64e..e2a530050d 100644 --- a/DOCS/tech/libao2.txt +++ b/DOCS/tech/libao2.txt @@ -23,16 +23,23 @@ static void reset(); static int get_space(); Returns how many bytes can be written into the audio buffer without - blocking (making caller process wait). If the buffer is (nearly) full, - has to return 0! - If it never gives 0, MPlayer won't work! + blocking (making caller process wait). MPlayer occasionally checks the + remaining space and tries to fill the buffer with play() if there's free + space. The buffer size used should be sane; a buffer that is too small + could run empty before MPlayer tries filling it again (normally once per + video frame), a buffer that is too big would force MPlayer decode the file + far ahead trying to find enough audio data to fill it. static int play(void* data,int len,int flags); Plays a bit of audio, which is received throught the "data" memory area, with - a size of "len". The "flags" isn't used yet. It has to copy the data, because - they can be overwritten after the call is made. Doesn't really have to use - all the bytes, it has to give back how many have been used (copied to - buffer). + a size of "len". It has to copy the data, because they can be overwritten + after the call is made. Doesn't have to use all the bytes; it has to + return the number of bytes used used (copied to buffer). If + flags|AOPLAY_FINAL_CHUNK is true then this is the last audio in the file. + The purpose of this flag is to tell aos that round down the audio played + from "len" to a multiple of some chunksize that this "len" should not be + rounded down to 0 or the data will never be played (as MPlayer will never + call play() with a larger len). static float get_delay(); Returns how long time it will take to play the data currently in the @@ -40,58 +47,10 @@ static float get_delay(); on this! In the worst case, return the maximum delay. !!! Because the video is synchronized to the audio (card), it's very important -!!! that the get_space and get_delay functions are correctly implemented! +!!! that the get_delay function is correctly implemented! -6.a audio plugins - Audio plugins are used for processing the audio data before it - reaches the soundcard driver. A plugin can change the following - aspects of the audio data stream: - 1. Sample format - 2. Sample rate - 3. Number of channels - 4. The data itself (i.e. filtering and other sound effects) - 5. The delay (almost all plugins does this) - The plugin interface is implemented as a pseudo device driver with - the catchy name "plugin". The plugins are executed sequentially - ordered by the "-aop list=plugin1,plugin2,..." command line switch. - To add plugins add an entry in audio_plugin.h the makefile and - create a source file named "pl_whatever.c". Input parameters are - added to audio_plugin.h and to cfg-mplayer.h. A good starting point - for writing plugins is pl_delay.c. Below is a description of what - the functions does: - -static int control(int cmd, int arg); - This is for reading/setting plugin-specific and other special - parameters and can be used for keyboard input for example. All - plugins must respond to cmd=AOCONTROL_PLUGIN_SET_LEN which is part - of the initialization of the plugin. When this command is received - the parameter pl_delay.len will contain the maximum size of data the - plugin can produce. This can be used for calculating and allocating - buffer space for the plugin. Before the function exits the parameter - pl_delay.len must be set to the maximum data size the plugin can - receive. Return CONTROL_OK for success and CONTROL_ERROR for fail, - other control codes are found in audio_out.h. - -static int init(); - This function is for initializing the plugin, it is called once - before the playing is started. In this function the plugin can read - AND write to the ao_plugin_data struct to determine and set input - and output parameters. It is important to write to the - ao_plugin_data.sz_mult and ao_plugin_data.delay_fix parameters if - the plugin changes the data size or adds delay. Return 0 for fail - and 1 for success. - -static void uninit() - Called before mplayer exits. Used for deallocating dynamic buffers. - -static void reset() - Called during reset can be used to empty buffers. MPlayer calls this - function when pause is pressed. - -static int play() - Called for every block of audio data sent through the plugin. This - function should be optimized for speed. The incoming data is found - in ao_plugin_data.data having length ao_plugin_data.len. These two - parameters should be changed by the plugin. Return 1 for success and - 0 for fail. +static void audio_pause(void); + Pause playing but do not delete buffered data if possible. +static void audio_resume(void); + Continue playing after audio_pause(). |