Hello,

I'm having a problem with audio rendering in Vegas Pro 16.424.

On a random basis, VP16 renders an AC3 file with no audio. The template is Dolby Digital AC3 Studio, 5.1 Surround DVD. When this happens, I re-render the AC3 audio and the output file has audio and looks OK. It's a hit-or-miss thing, occurring randomly. Sometimes I get audio, sometimes I don't. I make no changes to the Vegas project between attempts.

NOTE: the input audio is MP4/AAC stereo. I generate the 5.1 tracks using the V.I Stereo to 5.1 Converter in VP16. It's an Fx add-on that's worked OK in previous versions of Vegas, and in builds of VP 16 before 424.

I check for the presence of audio in the output AC3 file by:
1. playing the file in Windows Media Player or VLC Media Player
2. examining the audio tracks in Audacity.

I have to take these steps because the size of the output AC3 file with or without audio is exactly the same. In fact, for the file without audio, Audacity even shows the correct number of tracks - they're just all flat-lined.

Any idea what could be causing this on a random basis?

The input media in Vegas Pro is an MP4 file with both the video and audio tracks.

Below are the InfoMedia reports for the MP4 input audio, an AC3 rendered file with audio, and an AC3 file without audio. The AC3 with or without audio looks the same to me.

MP4 Audio:

ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 1 h 41 min
Duration_LastFrame                       : -21 ms
Bit rate mode                            : Constant
Bit rate                                 : 192 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 138 MiB (1%)
Language                                 : English
Default                                  : Yes
Alternate group                          : 1

AC3 Render Output with audio:

Audio
Format                                   : AC-3
Format/Info                              : Audio Coding 3
Commercial name                          : Dolby Digital
Duration                                 : 2 h 24 min
Bit rate mode                            : Constant
Bit rate                                 : 448 kb/s
Channel(s)                               : 6 channels
Channel layout                           : L R C LFE Ls Rs
Sampling rate                            : 48.0 kHz
Frame rate                               : 31.250 FPS (1536 SPF)
Bit depth                                : 16 bits
Compression mode                         : Lossy
Stream size                              : 463 MiB (100%)
Service kind                             : Complete Main

AC3 Render Output without audio:

Format                                   : AC-3
Format/Info                              : Audio Coding 3
Commercial name                          : Dolby Digital
Duration                                 : 2 h 24 min
Bit rate mode                            : Constant
Bit rate                                 : 448 kb/s
Channel(s)                               : 6 channels
Channel layout                           : L R C LFE Ls Rs
Sampling rate                            : 48.0 kHz
Frame rate                               : 31.250 FPS (1536 SPF)
Bit depth                                : 16 bits
Compression mode                         : Lossy
Stream size                              : 463 MiB (100%)
Service kind                             : Complete Main

Thanks for your time,
Alan Mintaka