When recording externally with a SONY Alpha 7 please make sure to select in the menu:
-> Audio Out Timing -> 'Lip Sync'
If the other option 'Live' is selected audio and video on the HDMI output won't be recorded in sync. The reason is that the camera needs a longer time to process video images in relation to the sound files which leads to an echo while monitoring. The 'Live' option intends to correct the echo by shifting the audio relating to the video. But only the 'Lip Sync' option outputs the video and audio in sync.