It sounds like a few things are going on:
I'll assume the term "lag" more accurately means, "it's playing in fits & starts -- it's not smooth playback". Here's why:
In there, you'll also find a link to make files that play back smoothly.
Why is there no audio? Probably because the audio check box wasn't checked in the Output Module in the AE Render Queue. Here's more:
And the most common reason for a too-short file is an incorrectly-adjusted Work Area in the comp being rendered. To fix this, open the comp. Hit the Home key. Hit the b key to set the beginning of the Work Area. Hit the End key. Hit the n key to set the end of the work area. The Work Area is now the same as the comp's duration. If the comp is longer than the intended file length, just adjust the end of the work area.
This sounds like a bandwidth issue.
That is to say, the file is requiring a higher data transfer rate than the storage media is able to provide.
If you render from After Effects using the Best Settings and Lossless templates, it's very easy to get a file with a high band with requirements.
For low band with files with good picture quality, I like to use the H264 format. I usually use one of the Vimeo presets in Adobe Media Encoder.
If you write back with the frame size and frame rate of the movie file, I can suggest a preset for you.
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