[linux-dvb] RFC 0.3: MPEG encoding and decoding V4L2/DVB API additions

Oliver Endriss o.endriss at gmx.de
Thu Feb 22 18:58:34 CET 2007


Hi,

see below for a some comments.

Hans Verkuil wrote:
> RFC MPEG encoding and decoding V4L2/DVB API additions
> Version 0.3
> ...
> MPEG Decoding commands
> ----------------------
> 
> In this section I will examine how to implement the decoding 
> functionality of the conexant cx23415 in terms of the DVB API, and 
> what, if any, additions to that API are needed to support it fully.
> 
> 1) Start/Stop/Pause/Resume decoding
> 
> After discussing this with Ralph it became clear that it was best to add 
> two new ioctls (as designed in the first version of this RFC) since the 
> existing VIDEO_PLAY/STOP/FREEZE/CONTINUE did not provide the required 
> functionality. The existing ioctls can still be used, but only do the 
> simple action. For more refined control (and better support for future 
> extensions) new VIDEO_COMMAND and VIDEO_TRY_COMMAND ioctls are added. 
> This ensures that existing apps won't break, but that the cx23415 is 
> still fully supported. Also future extensions are much easier.
> 
> #define VIDEO_CMD_PLAY        (0)
> #define VIDEO_CMD_STOP        (1)
> #define VIDEO_CMD_FREEZE      (2)
> #define VIDEO_CMD_CONTINUE    (3)
> 
> /* Flags for VIDEO_CMD_CONTINUE */
> #define VIDEO_CMD_PAUSE_TO_BLACK     (1 << 0)
> 
> /* Flags for VIDEO_CMD_STOP */
> #define VIDEO_CMD_STOP_TO_BLACK      (1 << 0)
> 
> /* Flags for VIDEO_CMD_PLAY */
> #define VIDEO_CMD_PLAY_SPEED_MUTE_AUDIO   (1 << 0)

Hm - is this really necessary?
The application could simply use AUDIO_SET_MUTE instead.

> ...
> 5) Audio mode selection
> 
> The cx23415 allows automatic selection of the audio mode (stereo, left, 
> right, mono or swapped channels) for both a normal stereo capture and a 
> bilingual capture.
> 
> The AUDIO_CHANNEL_SELECT ioctl comes close. If the 
> audio_channel_select_t enum was extended with AUDIO_MONO and 
> AUDIO_STEREO_SWAPPED and a AUDIO_BILINGUAL_CHANNEL_SELECT ioctl was 
> added, then this would fully implement this feature.

How is AUDIO_BILINGUAL_CHANNEL_SELECT supposed to work?
The av7110 driver uses AUDIO_MONO_LEFT/AUDIO_MONO_RIGHT to select the
channel.

CU
Oliver

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