[FFmpeg-devel] [PATCH 5/8] lavd: add device capabilities API

[Don Moir]

----- Original Message ----- 
From: "Lukasz Marek" <lukasz.m.luki2 at gmail.com>
To: <ffmpeg-devel at ffmpeg.org>
Sent: Wednesday, April 09, 2014 8:11 PM
Subject: Re: [FFmpeg-devel] [PATCH 5/8] lavd: add device capabilities API


> >
>> /**
>> + * Following API allows user to probe device capabilities (supported
>> codecs,
>> + * pixel formats, sample formats, resolutions, channel counts, etc).
>> + * It is build on top op AVOption API.
>> + * Queried capabilities allows to set up converters of video or audio
>> + * parameters that fit to the device.
>> + *
>> + * List of capablities that can be queried:
>> + *  - Capabilities valid for both audio and video devices:
>> + *    - codec:          supported audio/video codecs.
>> + *                      type: AV_OPT_TYPE_INT (AVCodecID value)
>> + *  - Capabilities valid for audio devices:
>> + *    - sample_format:  supported sample formats.
>> + *                      type: AV_OPT_TYPE_INT (AVSampleFormat value)
>> + *    - sample_rate:    supported sample rates.
>> + *                      type: AV_OPT_TYPE_INT
>> + *    - channels:       supported number of channels.
>> + *                      type: AV_OPT_TYPE_INT
>> + *    - channel_layout: supported channel layouts.
>> + *                      type: AV_OPT_TYPE_INT64
>>
>> Following should be: *  - Capabilities valid for video devices:
>
> yes, fixed locallly, thx
>
>> + *  - Capabilities valid for audio devices:
>>
>> + *    - pixel_format:   supported pixel formats.
>> + *                      type: AV_OPT_TYPE_INT (AVPixelFormat value)
>> + *    - window_size:    supported window sizes (describes size of the
>> window size presented to the user).
>> + *                      type: AV_OPT_TYPE_IMAGE_SIZE
>> + *    - frame_size:     supported frame sizes (describes size of
>> provided video frames).
>> + *                      type: AV_OPT_TYPE_IMAGE_SIZE
>> + *    - fps:            supported fps values
>> + *                      type: AV_OPT_TYPE_RATIONAL
>>
>> FPS can be a range for capture devices
>
> It can be a range by now.

Did you mean: by how or by now :)

+typedef struct AVDeviceCapabilitiesQuery {
+    const AVClass *class;
+    AVFormatContext *device_context;
+    enum AVCodecID codec;
+    enum AVSampleFormat sample_format;
+    enum AVPixelFormat pixel_format;
+    int sample_rate;
+    int channels;
+    int64_t channel_layout;
+    int window_width;
+    int window_height;
+    int frame_width;
+    int frame_height;
+    AVRational fps;
+} AVDeviceCapabilitiesQuery;

For a capture device and for each pixel format, width, and height, there can be a range of FPS values, like a min of a 1 FPS to max 
60 FPS. Just varies for each device and format. So don't see how that fits into the AVDeviceCapabilitiesQuery structure as it 
stands.