Changing Audio Bitrate; Numerous Caution Messages!!

[meeshu]

Attempting to change the bitrates of quite a few audio sample encoded via vorbis; ie ogg audio files.

The source files don't have an extension (.ogg), but are .ogg files as confirmed by analysing file headers.

Via ffmpeg, just doing a simple bitrate change using the command -

ffmpeg -i input [ogg file with no extension] -codec:a libvorbis -b:a 128k [ogg file with no extension]_128k.ogg

ffmpeg then produces numerous caution messages like -


[Attachment 78466 - Click to enlarge]

But despite these messages, output ogg files are still being output.

I've checked the length (in time) of the source and output files and they seem to be the same length of the time, but not always (maybe out by a few milliseconds).

I've played back both the source and output files and they sound about the same.

Should I be concerned about these caution messages?

Here is a sample source extensionless ogg file

[davexnet]

Seems to be a valid file, sans the extension.
You could try adding this code before the output file name

-af "aresample=async=1:first_pts=0"

https://superuser.com/questions/1042988/ffmpeg-audio-out-of-sync-when-transcoding-demuxing-from-dv

[meeshu]

Thanks for the suggestion!

I added the above command and there is no longer any caution messages appearing! The output ogg file seems to be of the same length as the source, and when played back also seems to be the same as the source.

So this added command works.

But I don't quite understand what caused the initial caution messages to occur? Especially the "queue input is backward in time" message? What on earth does that mean?

[davexnet]

I don't know the technical reason, but it appears to occur when converting ogg > ogg.
Seems to be related to massaging the file to deal with timing problems. More info here:
http://underpop.online.fr/f/ffmpeg/help/aresample.htm.gz

Perhaps somebody else can explain further (then we'll both learn something!)