RFC: Proposal for a V4L2 decoder API ------------------------------------ This RFC is based on this discussion: http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg32703.html The purpose is to remove the dependency of ivtv to the ioctls in dvb/audio.h and dvb/video.h. The summary of the posting referred to above is: - Add two controls to select the audio output channels. - Add two read-only controls for the PTS and frame count. - Copy and paste the old VIDEO_(TRY_)COMMAND to VIDIOC_(TRY_)DECODER_CMD. So, here is the RFC that does that. I'm going through the items from the summary in reverse order. 1) Add new VIDIOC_TRY_DECODER_CMD and VIDIOC_DECODER_CMD ioctls. These are the decoder counterparts of the VIDIOC_(TRY_)ENCODER_CMD ioctls that are already in V4L2. /* Decoder commands */ #define V4L2_DEC_CMD_PLAY (0) #define V4L2_DEC_CMD_STOP (1) #define V4L2_DEC_CMD_FREEZE (2) #define V4L2_DEC_CMD_CONTINUE (3) /* Flags for V4L2_DEC_CMD_FREEZE */ #define V4L2_DEC_CMD_FREEZE_TO_BLACK (1 << 0) /* Flags for V4L2_DEC_CMD_STOP */ #define V4L2_DEC_CMD_STOP_TO_BLACK (1 << 0) #define V4L2_DEC_CMD_STOP_IMMEDIATELY (1 << 1) /* Play format requirements (returned by the driver): */ /* The decoder has no special format requirements */ #define V4L2_DEC_PLAY_FMT_NONE (0) /* The decoder requires full GOPs */ #define V4L2_DEC_PLAY_FMT_GOP (1) /* The structure must be zeroed before use by the application This ensures it can be extended safely in the future. */ struct v4l2_decoder_cmd { __u32 cmd; __u32 flags; union { struct { /* Stop when this PTS is reached */ __u64 pts; } stop; struct { /* 0 or 1000 specifies normal speed, 1 specifies forward single stepping, -1 specifies backward single stepping, >1: playback at speed/1000 of the normal speed, <-1: reverse playback at (-speed/1000) of the normal speed. */ __s32 speed; __u32 format; } play; struct { __u32 data[16]; } raw; }; }; Other than renaming the #defines and struct there are no changes compared to the current video.h API. I see no reason to change this either. 2) Add read-only controls for the PTS and framecount. V4L2_CID_MPEG_STREAM_DEC_PTS - integer64 Return the PTS (Presentation Time Stamp) of the currently presented frame. V4L2_CID_MPEG_VIDEO_DEC_FRAME - integer Return the frame number of the currently presented frame. When the decoder starts the frame counter is reset to 0. 3) Add two new audio selection controls. V4L2_CID_MPEG_AUDIO_DEC_CHANNEL - menu Select how to playback stereo audio from a normal audio stream: 0 - Auto (playback native format) 1 - Left (left channel only) 2 - Right (right channel only) 3 - Stereo 4 - Swapped Stereo (I'm not sure whether this should be added. Is this ever useful?) This control relates to its encoder counterpart V4L2_CID_MPEG_AUDIO_MODE for the non-DUAL modes. V4L2_CID_MPEG_AUDIO_DEC_MULTILINGUAL_CHANNEL - menu Select how to playback audio from a multilingual audio stream: 0 - Auto (either always Left or can be based on some preferred language) 1 - Left (left channel only) 2 - Right (right channel only) 3 - Stereo 4 - Swapped Stereo (I'm not sure whether this should be added. Is this ever useful?) This control relates to its encoder counterpart V4L2_CID_MPEG_AUDIO_MODE for the DUAL mode. Note that these two controls are specific to the audio layer I/II/III audio mode setting. They do not support any e.g. AAC decoding. More research will need to be done to know whether that makes sense or not. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
