Allocate enough data in buffer to hold an RTP packet with csrc_count CSRCs,
a payload length of payload_len and padding of pad_len.
buffer must be writable and all previous memory in buffer will be freed.
If pad_len is >0, the padding bit will be set. All other RTP header fields
will be set to 0/FALSE.
Allocate enough data in buffer to hold an RTP packet with csrc_count CSRCs, a payload length of payload_len and padding of pad_len. buffer must be writable and all previous memory in buffer will be freed. If pad_len is >0, the padding bit will be set. All other RTP header fields will be set to 0/FALSE.