Bit depth in the container format vs. in the output

[Carlos Rafael Giani]

Hello,

there is a problem with displaying file type information. Suppose I want
to show a file's bit depth on screen. The intuitive solution is to use
the caps that come out of a uridecodebin for example, and look at its
format value. But this can be misleading.

For example, if in a system, avdec_flac is used instead of flacdec, then
the format value will be S32LE even if the actual internal FLAC data
format is S24_32LE. So now all of a sudden the display shows "32 bit",
even though "24 bit" is more correct.

This is even visible with gst-discoverer. If you have a 24-bit FLAC
file, and run gst-discoverer-1.0 -v <flacfile> , the output with flacdec
present is:

     Channels: 2
     Sample rate: 192000
     Depth: 24
     Bitrate: 0
     Max bitrate: 0

but with flacdec missing (so only avdec_flac is available) it is:

     Channels: 2
     Sample rate: 192000
     Depth: 32
     Bitrate: 0
     Max bitrate: 0

So, the correct way to do this is to get the caps that *flacparse*
outputs, and not the decoder's. However, I have no clue how to do that,
or even how to communicate such information to the application properly.
There is no tag that can hold a GstCaps instance.

Any ideas?
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[Arun Raghavan-4]

On Wed, 13 Jul 2016, at 07:08 PM, Carlos Rafael Giani wrote:

> Hello,
>
> there is a problem with displaying file type information. Suppose I want
> to show a file's bit depth on screen. The intuitive solution is to use
> the caps that come out of a uridecodebin for example, and look at its
> format value. But this can be misleading.
>
> For example, if in a system, avdec_flac is used instead of flacdec, then
> the format value will be S32LE even if the actual internal FLAC data
> format is S24_32LE. So now all of a sudden the display shows "32 bit",
> even though "24 bit" is more correct.
>
> This is even visible with gst-discoverer. If you have a 24-bit FLAC
> file, and run gst-discoverer-1.0 -v <flacfile> , the output with flacdec
> present is:
>
>      Channels: 2
>      Sample rate: 192000
>      Depth: 24
>      Bitrate: 0
>      Max bitrate: 0
>
> but with flacdec missing (so only avdec_flac is available) it is:
>
>      Channels: 2
>      Sample rate: 192000
>      Depth: 32
>      Bitrate: 0
>      Max bitrate: 0
>
> So, the correct way to do this is to get the caps that *flacparse*
> outputs, and not the decoder's. However, I have no clue how to do that,
> or even how to communicate such information to the application properly.
> There is no tag that can hold a GstCaps instance.
>
> Any ideas?

At one point we had toyed with the idea of having a "shallow" mode in
GstDiscoverer -- basically get it to stop at the point of plugging a
parser. Perhaps this is worth resurrecting?

-- Arun
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[Jonathan Miles]

Hi

I recently came across the same problem and got round it by adding a meta-data tag 'bits-per-sample' and setting it in the wav, flac, alac and aiff parsers.

The patches are attached. bits-per-sample applies to gstreamer1.0, aiff-bits-per-sample-tag applies to gstreamer1.0-plugins-bad, alac-flac-wav-bits-per-sample-tag applies to gstreamer1.0-plugins-good.

Hope that helps,

Jonathan

---

From: gstreamer-devel <[hidden email]> on behalf of Arun Raghavan <[hidden email]>
Sent: 14 July 2016 07:49
To: Discussion of the development of and with GStreamer
Subject: Re: Bit depth in the container format vs. in the output

 

On Wed, 13 Jul 2016, at 07:08 PM, Carlos Rafael Giani wrote:
> Hello,
>
> there is a problem with displaying file type information. Suppose I want
> to show a file's bit depth on screen. The intuitive solution is to use
> the caps that come out of a uridecodebin for example, and look at its
> format value. But this can be misleading.
>
> For example, if in a system, avdec_flac is used instead of flacdec, then
> the format value will be S32LE even if the actual internal FLAC data
> format is S24_32LE. So now all of a sudden the display shows "32 bit",
> even though "24 bit" is more correct.
>
> This is even visible with gst-discoverer. If you have a 24-bit FLAC
> file, and run gst-discoverer-1.0 -v <flacfile> , the output with flacdec
> present is:
>
>      Channels: 2
>      Sample rate: 192000
>      Depth: 24
>      Bitrate: 0
>      Max bitrate: 0
>
> but with flacdec missing (so only avdec_flac is available) it is:
>
>      Channels: 2
>      Sample rate: 192000
>      Depth: 32
>      Bitrate: 0
>      Max bitrate: 0
>
> So, the correct way to do this is to get the caps that *flacparse*
> outputs, and not the decoder's. However, I have no clue how to do that,
> or even how to communicate such information to the application properly.
> There is no tag that can hold a GstCaps instance.
>
> Any ideas?

At one point we had toyed with the idea of having a "shallow" mode in
GstDiscoverer -- basically get it to stop at the point of plugging a
parser. Perhaps this is worth resurrecting?

-- Arun
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