fallbacksrc: support multiple video and audio tracks

I'm using the fallbacksrc element to consume two SRT sources as:

export GST_DEBUG_DUMP_DOT_DIR=/tmp
gst-launch-1.0 fallbacksrc uri="srt://SOME_IP:10001?mode=caller" fallback-uri="srt://SOME_IP:10005?mode=caller" timeout=500000000 name="decodebin" \
  decodebin.video ! queue ! fakesink \
  decodebin.audio ! queue ! fakesink

The fallbacksrc works as expected in this case.

However, if my SRT sources contain more than one video or audio track, I'm not able to collect the decoded data out of the fallbacksrc as there are no video_%u nor audio_%u pads I could use to request the data. Ideally, I would like:

export GST_DEBUG_DUMP_DOT_DIR=/tmp
gst-launch-1.0 fallbacksrc uri="srt://SOME_IP:10001?mode=caller" fallback-uri="srt://SOME_IP:10005?mode=caller" timeout=500000000 name="decodebin" \
  decodebin.video_0 ! queue ! fakesink \
  decodebin.video_1 ! queue ! fakesink \
  decodebin.video_2 ! queue ! fakesink \
  decodebin.video_3 ! queue ! fakesink \
  decodebin.video_4 ! queue ! fakesink \
  decodebin.audio_0 ! queue ! fakesink \
  decodebin.audio_1 ! queue ! fakesink

Here's a diagram with the pipeline when there are 5 video and 2 audio tracks. The underlying uridecodebin3 is detecting all the tracks, but it is decoding video_0 and audio_0 only.

The enhancement I propose is to expose all available tracks as source pads of the fallbacksrc element as audio_%u, video_%u. Looking at the documentation of the element, the pad templates are audio and video, without the typical _%u suffix of multiple pads. Not sure if they can be modified without breaking the current element API, or if this will require a new fallbacksrc2 element.

I'm happy to contribute to enhancing the element if needed.