[FFmpeg-user] Opus : difference between .opus and .ogg file extension

[Kieran O Leary]

Hi

On Thu, Nov 30, 2017 at 10:24 AM,  <nerbrume at free.fr> wrote:
> Hello all,
>
> I'm encoding my audio files to opus, with the following command:
>> ffmpeg -i test.mp3 -acodec libopus -b:a 64000 -vbr on test.opus
> (Debian squeeze, ffmpeg version 3.3.5)
>
> According to wikipedia, the "opus" container should just be an ogg container (https://en.wikipedia.org/wiki/Opus_%28audio_format%29).
> However, encoding my file with an ogg extension :
>> ffmpeg -i test.mp3 -acodec libopus -b:a 64000 -vbr on test.ogg
> produces a different file from the previous one (md5 are mismatched).
>

I know nothing about these formats really, but using md5 for this kind
of comparison is sometimes flawed. With some formats, pieces of
metadata like 'encoded date', or perhaps a unique ID can be written.
So each time you run the same ffmpeg command, you will get a different
whole file MD5 value as a few small bits will indeed be different.

I mimicked your command and produced opus and ogg outputs from the
same input. Using mediainfo's trace feature, it looks to me like both
are pretty much identical, they just have different values for 'stream
serial number' and 'page checksum'. It looks to me as though both
files are pretty much identical otherwise. Here's the output of both
trace reports:
https://gist.github.com/kieranjol/45edc4871270ce6110d256590e71e229

I used
mediainfo --Details=1 test.ogg
mediainfo --Details=1 test.opus

to get those outputs.

Best,

Kieran.