[FFmpeg-devel,v5,08/13] avdevice/dshow: list_devices: show media type(s) per device

the list_devices option of dshow didn't indicate whether a specific
device provides audio or video output. This patch iterates through all
media formats of all pins exposed by the device to see what types it
provides for capture, and prints this to the console for each device.
Importantly, this now allows to find devices that provide both audio and
video, and devices that provide neither.

Signed-off-by: Diederick Niehorster <dcnieho@gmail.com>
---
 libavdevice/dshow.c | 103 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 98 insertions(+), 5 deletions(-)

Diederick Niehorster:
> the list_devices option of dshow didn't indicate whether a specific
> device provides audio or video output. This patch iterates through all
> media formats of all pins exposed by the device to see what types it
> provides for capture, and prints this to the console for each device.
> Importantly, this now allows to find devices that provide both audio and
> video, and devices that provide neither.
> 
> Signed-off-by: Diederick Niehorster <dcnieho@gmail.com>
> ---
>  libavdevice/dshow.c | 103 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 98 insertions(+), 5 deletions(-)
> 
> diff --git a/libavdevice/dshow.c b/libavdevice/dshow.c
> index 8c257ca8e7..f25537db5c 100644
> --- a/libavdevice/dshow.c
> +++ b/libavdevice/dshow.c
> @@ -197,6 +197,79 @@ fail:
>      return;
>  }
>  
> +static void dshow_get_device_media_types(AVFormatContext *avctx, enum dshowDeviceType devtype,
> +                                         enum dshowSourceFilterType sourcetype, IBaseFilter *device_filter,
> +                                         enum AVMediaType **media_types, int *nb_media_types)
> +{
> +    struct dshow_ctx *ctx = avctx->priv_data;
> +    IEnumPins *pins = 0;
> +    IPin *pin;
> +    int has_audio = 0, has_video = 0;
> +
> +    if (IBaseFilter_EnumPins(device_filter, &pins) != S_OK)
> +        return;
> +
> +    while (IEnumPins_Next(pins, 1, &pin, NULL) == S_OK) {
> +        IKsPropertySet *p = NULL;
> +        PIN_INFO info = { 0 };
> +        GUID category;
> +        DWORD r2;
> +        IEnumMediaTypes *types = NULL;
> +        AM_MEDIA_TYPE *type;
> +
> +        if (IPin_QueryPinInfo(pin, &info) != S_OK)
> +            goto next;
> +        IBaseFilter_Release(info.pFilter);
> +
> +        if (info.dir != PINDIR_OUTPUT)
> +            goto next;
> +        if (IPin_QueryInterface(pin, &IID_IKsPropertySet, (void **) &p) != S_OK)
> +            goto next;
> +        if (IKsPropertySet_Get(p, &AMPROPSETID_Pin, AMPROPERTY_PIN_CATEGORY,
> +                               NULL, 0, &category, sizeof(GUID), &r2) != S_OK)
> +            goto next;
> +        if (!IsEqualGUID(&category, &PIN_CATEGORY_CAPTURE))
> +            goto next;
> +
> +        if (IPin_EnumMediaTypes(pin, &types) != S_OK)
> +            goto next;
> +
> +        // enumerate media types exposed by pin
> +        // NB: don't know if a pin can expose both audio and video, check 'm all to be safe
> +        IEnumMediaTypes_Reset(types);
> +        while (IEnumMediaTypes_Next(types, 1, &type, NULL) == S_OK) {
> +            if (IsEqualGUID(&type->majortype, &MEDIATYPE_Video)) {
> +                has_video = 1;
> +            } else if (IsEqualGUID(&type->majortype, &MEDIATYPE_Audio)) {
> +                has_audio = 1;
> +            }
> +            CoTaskMemFree(type);
> +        }
> +
> +    next:
> +        if (types)
> +            IEnumMediaTypes_Release(types);
> +        if (p)
> +            IKsPropertySet_Release(p);
> +        if (pin)
> +            IPin_Release(pin);
> +    }
> +
> +    IEnumPins_Release(pins);
> +
> +    if (has_audio || has_video) {
> +        int nb_types = has_audio + has_video;
> +        *media_types = av_malloc_array(nb_types, sizeof(enum AVMediaType));

You are allocating a list of at most two entries; why not put an array
of that many entries on the stack in dshow_cycle_devices() and write
them there. This would get rid of the allocations, the frees and would
fix the problem that you do not forward the error in case of allocation
failure.
(The required size of said array should of course be defined by a macro.)

> +        if (*media_types) {
> +            if (has_audio)
> +                (*media_types)[0] = AVMEDIA_TYPE_AUDIO;
> +            if (has_video)
> +                (*media_types)[0 + has_audio] = AVMEDIA_TYPE_VIDEO;
> +            *nb_media_types = nb_types;
> +        }
> +    }
> +}
> +
>  /**
>   * Cycle through available devices using the device enumerator devenum,
>   * retrieve the device with type specified by devtype and return the
> @@ -242,6 +315,8 @@ dshow_cycle_devices(AVFormatContext *avctx, ICreateDevEnum *devenum,
>          LPOLESTR olestr = NULL;
>          LPMALLOC co_malloc = NULL;
>          AVDeviceInfo *device = NULL;
> +        enum AVMediaType *media_types = NULL;
> +        int nb_media_types = 0;
>          int i;
>  
>          r = CoGetMalloc(1, &co_malloc);
> @@ -286,6 +361,12 @@ dshow_cycle_devices(AVFormatContext *avctx, ICreateDevEnum *devenum,
>                  // success, loop will end now
>              }
>          } else {
> +            // get media types exposed by pins of device
> +            if (IMoniker_BindToObject(m, 0, 0, &IID_IBaseFilter, (void* ) &device_filter) == S_OK) {
> +                dshow_get_device_media_types(avctx, devtype, sourcetype, device_filter, &media_types, &nb_media_types);
> +                IBaseFilter_Release(device_filter);
> +                device_filter = NULL;
> +            }
>              if (device_list) {
>                  device = av_mallocz(sizeof(AVDeviceInfo));
>                  if (!device)
> @@ -306,12 +387,26 @@ dshow_cycle_devices(AVFormatContext *avctx, ICreateDevEnum *devenum,
>                  device = NULL;  // copied into array, make sure not freed below
>              }
>              else {
> -                av_log(avctx, AV_LOG_INFO, " \"%s\"\n", friendly_name);
> -                av_log(avctx, AV_LOG_INFO, "    Alternative name \"%s\"\n", unique_name);
> +                av_log(avctx, AV_LOG_INFO, "\"%s\"", friendly_name);
> +                if (nb_media_types > 0 && media_types) {

You are checking both the number of media types as well as the pointer;
the second check is redundant if you never set the number inconsistently
(which you don't).

> +                    const char* media_type = av_get_media_type_string(media_types[0]);
> +                    av_log(NULL, AV_LOG_INFO, " (%s", media_type ? media_type : "unknown");

av_log(NULL should be avoided. Use a proper logcontext.

> +                    for (int i = 1; i < nb_media_types; ++i) {
> +                        media_type = av_get_media_type_string(media_types[i]);
> +                        av_log(NULL, AV_LOG_INFO, ", %s", media_type ? media_type : "unknown");
> +                    }
> +                    av_log(NULL, AV_LOG_INFO, ")");
> +                } else {
> +                    av_log(NULL, AV_LOG_INFO, " (none)");
> +                }
> +                av_log(avctx, AV_LOG_INFO, "\n");
> +                av_log(avctx, AV_LOG_INFO, "  Alternative name \"%s\"\n", unique_name);
>              }
>          }
>  
> -fail1:
> +    fail1:
> +        if (media_types)
> +            av_freep(&media_types);
>          if (device) {
>              if (device->device_name)
>                  av_freep(&device->device_name);
> @@ -1186,9 +1281,7 @@ static int dshow_read_header(AVFormatContext *avctx)
>      }
>  
>      if (ctx->list_devices) {
> -        av_log(avctx, AV_LOG_INFO, "DirectShow video devices (some may be both video and audio devices)\n");
>          dshow_cycle_devices(avctx, devenum, VideoDevice, VideoSourceDevice, NULL, NULL, NULL);
> -        av_log(avctx, AV_LOG_INFO, "DirectShow audio devices\n");
>          dshow_cycle_devices(avctx, devenum, AudioDevice, AudioSourceDevice, NULL, NULL, NULL);
>          ret = AVERROR_EXIT;
>          goto error;
>