For Some Media Files Audio is Played over SPDIF, others Analog

[alx9r]

Here is what I am seeing:

For the vast majority of video files and (I think) all audio files in my collection sound is played through the coax SPDIF output.  However, for a few video files (perhaps 1 in 100) the audio is played on the analog output only.

Fortunately, both receivers i have used detect the audio source and switch inputs accordingly.  The main problem is that the analog audio is *much* quieter (>24dB) than that over SPDIF.

Has anyone else experienced this?


Here are some technical details:

Sound Hardware (According to alsamixer)
Card: HDA NVidia
Chip: Analog Devices AD1986A

I was able to extract some details from one of the files using VideoInspector.  The other file I had handy was not supported by Video Inspector.  Here is the output from the first one:

Code:

File Size : 2.23 Gb.

[Movie]
Valid : Yes [Matroska]
Duration : 00:11:00
Movie complete : Yes

[Video]
Resolution : 1080x1040
Codec : MPEG4 ISO advanced
FPS : 25.00
BitRate : 0 Kbps
Quality Factor : 0.00 b/px

[Audio]
Codec : AAC HE
Number of channels : 6
Sample Rate : 48000 Hz
BitRate : 0 Kbps

[colinjones]

Maybe your audio chip doesn't support pass-thru for that audio codec? Is it a different codec than video files that do work?

[alx9r]

Maybe your audio chip doesn't support pass-thru for that audio codec?

I thought that any codec-related processing took place at a much higher level in software and that the audio data passed to the actual audio hardware was rather raw.

Is it a different codec than video files that do work?

These same thought has crossed my mind.  I am currently looking for a tool that will allow me to inspect the encoding of my media files en masse.

[alx9r]

Is it a different codec than video files that do work?

I just found a different file with the same audio encoding (AAC HE) that plays over SPDIF. 

Here are the details from the file:

Code:

File Size : 1.37 Gb.

[Movie]
Valid : Yes [Matroska]
Duration : 00:56:31
Movie complete : Yes

[Video]
Resolution : 720x400
Codec : MPEG4 ISO advanced
FPS : 25.00
BitRate : 0 Kbps
Quality Factor : 0.00 b/px

[Audio]
Codec : AAC HE
Number of channels : 2
Sample Rate : 24000 Hz
BitRate : 0 Kbps