Simultaneously transcode multiple audio streams / caption

[elv-reza]

• Add the capability to transcode multiple different audio streams at the same time in one avpipe session.
• The stream index of audio streams can be passed to the avpipe session using xcparams_t (for mpegts might need to pass multiple stream id, if stream index doesn't work).
• All the audio streams have to have the same timebase.
• This specifically can be useful when transcoding a live stream with multiple audios and generating mezzanine files.
• In addition to capture and transcode different audio streams, it is needed to capture the caption at the same time.