I have saved a few downloaded video files as MP4 files to play on my
Roku player, using Wonderhare UniConverter. Sometimes I am getting an
error message 'Excessive AV skew'.

Is this a fault in the original video? Could it be overcome by using
the Video Converter option in UniConverter rather than the Merger
option? I am wondering if Merger is more likely to perpetuate errors.

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On Mon, 16 Jan 2023 12:21:14 +0000, Vir Campestris <vir.campestris@invalid.invalid> wrote:

On 16/01/2023 09:52, Scott wrote:

I have saved a few downloaded video files as MP4 files to play on my
Roku player, using Wonderhare UniConverter. Sometimes I am getting an
error message 'Excessive AV skew'.

Is this a fault in the original video? Could it be overcome by using
the Video Converter option in UniConverter rather than the Merger
option? I am wondering if Merger is more likely to perpetuate errors.

It would be interesting to know what the AV skew is.

I use ffmpeg to do this kind of thing, and I've had no problems. It is >available for Windows (I assume you are using Windows?)

There's a corresponding program ffprobe which allows you to look at the
file and find out things like timestamps on the frames.

Or you could try

https://support.roku.com/en-gb/

Thanks. I have looked at the Roku site and tried various suggestions
there. However, I would like to get to the bottom of why the file is
corrupted in the first place, as other files do not present the same difficulty. Hence my question here.

--- SoupGate-Win32 v1.05
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On 16/01/2023 09:52, Scott wrote:

I have saved a few downloaded video files as MP4 files to play on my
Roku player, using Wonderhare UniConverter. Sometimes I am getting an
error message 'Excessive AV skew'.

Is this a fault in the original video? Could it be overcome by using
the Video Converter option in UniConverter rather than the Merger
option? I am wondering if Merger is more likely to perpetuate errors.

It would be interesting to know what the AV skew is.

I use ffmpeg to do this kind of thing, and I've had no problems. It is available for Windows (I assume you are using Windows?)

There's a corresponding program ffprobe which allows you to look at the
file and find out things like timestamps on the frames.

Or you could try

https://support.roku.com/en-gb/

Andy

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On 16/01/2023 12:53, Scott wrote:

On Mon, 16 Jan 2023 12:21:14 +0000, Vir Campestris <vir.campestris@invalid.invalid> wrote:

On 16/01/2023 09:52, Scott wrote:

I have saved a few downloaded video files as MP4 files to play on my
Roku player, using Wonderhare UniConverter. Sometimes I am getting an
error message 'Excessive AV skew'.

Is this a fault in the original video? Could it be overcome by using
the Video Converter option in UniConverter rather than the Merger
option? I am wondering if Merger is more likely to perpetuate errors.

It would be interesting to know what the AV skew is.

I use ffmpeg to do this kind of thing, and I've had no problems. It is
available for Windows (I assume you are using Windows?)

There's a corresponding program ffprobe which allows you to look at the
file and find out things like timestamps on the frames.

Or you could try

https://support.roku.com/en-gb/

Thanks. I have looked at the Roku site and tried various suggestions
there. However, I would like to get to the bottom of why the file is corrupted in the first place, as other files do not present the same difficulty. Hence my question here.

In that case ffprobe is probably your best bet. Run it on the file with -show_frames, and look to see if there is much discrepancy between the timestamps on the audio and video streams.

ffmpeg will allow you to rewrite the file without re-encoding it
(-acodec copy -vcodec copy) and might sort it out for you.

Andy

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On 16/01/2023 17:35, Vir Campestris wrote:

ffmpeg will allow you to rewrite the file without re-encoding it
(-acodec copy -vcodec copy) and might sort it out for you.

How does the command know which stream (audio or video) has the correct timestamps, and which has the wrong ones which need to be copied from
the right stream? Does it look for abnormal timestamps (ie not
increasing from one sample to the next in roughly equal intervals of
time), and flag a stream with rogue samples as being the incorrect one?
What happens if both streams contain rogue timestamps though not
necessarily for the same samples and/or at the same instant?

How common is it for off-air recordings to contain valid samples with
incorrect timestamps, as opposed to missing/corrupted samples which get
dropped altogether in the playback decoder?

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On 16/01/2023 23:31, NY wrote:

On 16/01/2023 17:35, Vir Campestris wrote:

ffmpeg will allow you to rewrite the file without re-encoding it
(-acodec copy -vcodec copy) and might sort it out for you.

How does the command know which stream (audio or video) has the correct timestamps, and which has the wrong ones which need to be copied from
the right stream? Does it look for abnormal timestamps (ie not
increasing from one sample to the next in roughly equal intervals of
time), and flag a stream with rogue samples as being the incorrect one?
What happens if both streams contain rogue timestamps though not
necessarily for the same samples and/or at the same instant?

How common is it for off-air recordings to contain valid samples with incorrect timestamps, as opposed to missing/corrupted samples which get dropped altogether in the playback decoder?

The timestamps ought to be correct. The Skew message _probably_ means
that the difference in the location in the file of the packets for audio
and video with the same timestamps is too much.

Pulling the two streams out, then writing them back with the
corresponding timestamps closer ought to work.

Imagine the file is something like this:
A0
V0
V1
V2
V3
V4
V5
V6
V7
A1
V8
A2
V9
A3
...

so that the audio and video with the same time are a long way from each
other in space then you can get a problem.

Andy

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On 20/01/2023 12:19, Vir Campestris wrote:

The timestamps ought to be correct. The Skew message _probably_ means
that the difference in the location in the file of the packets for audio
and video with the same timestamps is too much.

Pulling the two streams out, then writing them back with the
corresponding timestamps closer ought to work.

Imagine the file is something like this:
A0
V0
V1
V2
V3
V4
V5
V6
V7
A1
V8
A2
V9
A3
...

so that the audio and video with the same time are a long way from each
other in space then you can get a problem.

Andy

I imagine that how much skew there can be before it causes a problem
depends on the player software.

Maybe the Roku is particularly fussy?

--
Brian Gregory (in England).

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On Monday, 16 January 2023 at 17:35:20 UTC, Vir Campestris wrote:

ffmpeg will allow you to rewrite the file without re-encoding it
(-acodec copy -vcodec copy) and might sort it out for you.

Andy

JOOI can this be used to put a movie in a different container, e.g. from avi to mp4?
What about removing certain audio tracks, leaving just the one I want?

Thanks.

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On 31/01/2023 22:14, David Paste wrote:

On Monday, 16 January 2023 at 17:35:20 UTC, Vir Campestris wrote:

ffmpeg will allow you to rewrite the file without re-encoding it
(-acodec copy -vcodec copy) and might sort it out for you.

Andy

JOOI can this be used to put a movie in a different container, e.g. from avi to mp4?
What about removing certain audio tracks, leaving just the one I want?

Yes. I've seen this done.

--
Brian Gregory (in England).

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On Wednesday, 1 February 2023 at 21:00:53 UTC, Brian Gregory wrote:

Yes. I've seen this done.
--
Brian Gregory (in England).

Cheers!

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On 01/02/2023 23:01, David Paste wrote:

On Wednesday, 1 February 2023 at 21:00:53 UTC, Brian Gregory wrote:

Yes. I've seen this done.
--
Brian Gregory (in England).

Cheers!

I run get_iplayer, and store the files in raw. Lately some things have
been coming in two files, audio and video separately. ffmpeg lets me
glue them back together into an mp4 file. There's even a switch to tell
it not to transcode.

Andy

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On 31/01/2023 22:14, David Paste wrote:

On Monday, 16 January 2023 at 17:35:20 UTC, Vir Campestris wrote:

ffmpeg will allow you to rewrite the file without re-encoding it
(-acodec copy -vcodec copy) and might sort it out for you.

Andy

JOOI can this be used to put a movie in a different container, e.g. from avi to mp4?
What about removing certain audio tracks, leaving just the one I want?

Thanks.

This seems to be an example of how to do it, in a simple case:

ffmpeg -i oldfile.avi -c copy newfile.mkv

That should repackage oldfile.avi as newfile.mkv without any recoding.

--
Brian Gregory (in England).

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On 05/02/2023 21:45, Brian Gregory wrote:

This seems to be an example of how to do it, in a simple case:

ffmpeg -i oldfile.avi -c copy newfile.mkv

That should repackage oldfile.avi as newfile.mkv without any recoding.

And adding the -ignore_unknown option would make it more robust for, for instance, packaging a .TS recording from a PVR into a MP4 or MKV by
telling it not to complain about the TV related stuff that isn't allowed
in an MP4 or MKV.

--
Brian Gregory (in England).

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On Sunday, 5 February 2023 at 21:45:22 UTC, Brian Gregory wrote:

This seems to be an example of how to do it, in a simple case:

ffmpeg -i oldfile.avi -c copy newfile.mkv

That should repackage oldfile.avi as newfile.mkv without any recoding.

You're a gent, thank you!

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