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Old 10-05-2010, 01:40 PM
Celejar
 
Default transcoding flv to mp4

Hi,

I'm dabbling in transcoding flvs (e.g., from YouTube) to mp4s (for
uploading to a service (Snapfish) which doesn't support flv. I'm doing
something like this:

ffmpeg -i example.flv example.mp4

I find that the above command line reduces the size of the video to
about a third of the original, but at the cost of egregious degradation
of the video quality. If I use the 'sameq' option:

ffmpeg -sameq -i example.flv example.mp4

the resulting video seems to retain the quality, but now the file size
is increased by a factor of four (I've only tested one file so far -
the original flv was about 20MB, the first mp4 was about 8MB, and the
second about 80MB).

Why is this, and is there a happy medium, i.e., a way to keep the size
roughly constant, but to retain quality?

Celejar
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Old 10-05-2010, 01:59 PM
Timo Juhani Lindfors
 
Default transcoding flv to mp4

Celejar <celejar@gmail.com> writes:
> ffmpeg -i example.flv example.mp4

I just get

Unsupported codec for output stream #0.1

on debian unstable with ffmpeg 4:0.5.2-4.


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Old 10-05-2010, 02:13 PM
Camaleón
 
Default transcoding flv to mp4

On Tue, 05 Oct 2010 09:40:46 -0400, Celejar wrote:

(...)

> Why is this, and is there a happy medium, i.e., a way to keep the size
> roughly constant, but to retain quality?

Play with "-qscale n" (n=1 better quality/bigger file, n=31 lower
quality, smaller file)

Greetings,

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Old 10-05-2010, 02:27 PM
Celejar
 
Default transcoding flv to mp4

[Please reply only to the list, as per the CoC.]

On Tue, 05 Oct 2010 16:59:04 +0300
Timo Juhani Lindfors <timo.lindfors@iki.fi> wrote:

> Celejar <celejar@gmail.com> writes:
> > ffmpeg -i example.flv example.mp4
>
> I just get
>
> Unsupported codec for output stream #0.1
>
> on debian unstable with ffmpeg 4:0.5.2-4.

I'm using 5:0.6~svn20100726-0.1 , from Marillat's repo.

Celejar
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Old 10-05-2010, 02:48 PM
Ron Johnson
 
Default transcoding flv to mp4

On 10/05/2010 08:40 AM, Celejar wrote:

Hi,

I'm dabbling in transcoding flvs (e.g., from YouTube) to mp4s (for
uploading to a service (Snapfish) which doesn't support flv. I'm doing
something like this:

ffmpeg -i example.flv example.mp4



Have you tried Handbrake? It's got a CLI mode, too.

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Old 10-05-2010, 03:11 PM
Celejar
 
Default transcoding flv to mp4

On Tue, 5 Oct 2010 14:13:07 +0000 (UTC)
Camaleón <noelamac@gmail.com> wrote:

> On Tue, 05 Oct 2010 09:40:46 -0400, Celejar wrote:
>
> (...)
>
> > Why is this, and is there a happy medium, i.e., a way to keep the size
> > roughly constant, but to retain quality?
>
> Play with "-qscale n" (n=1 better quality/bigger file, n=31 lower
> quality, smaller file)

Thanks - looks interesting. I've tried n=1 and n=10; the former seems
to give the identical file to -sameq, and the latter yields a file
slightly smaller than the flv, and of perhaps slightly worse quality.
I'll have to experiment more when I get a chance.

Celejar
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Old 10-05-2010, 03:12 PM
Celejar
 
Default transcoding flv to mp4

On Tue, 05 Oct 2010 09:48:49 -0500
Ron Johnson <ron.l.johnson@cox.net> wrote:

> On 10/05/2010 08:40 AM, Celejar wrote:
> > Hi,
> >
> > I'm dabbling in transcoding flvs (e.g., from YouTube) to mp4s (for
> > uploading to a service (Snapfish) which doesn't support flv. I'm doing
> > something like this:
> >
> > ffmpeg -i example.flv example.mp4
> >
>
> Have you tried Handbrake? It's got a CLI mode, too.

Thanks - I'll have to look into it.

Celejar
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Old 10-05-2010, 04:58 PM
Jochen Schulz
 
Default transcoding flv to mp4

Celejar:
>
> ffmpeg -i example.flv example.mp4
>
> I find that the above command line reduces the size of the video to
> about a third of the original, but at the cost of egregious degradation
> of the video quality. If I use the 'sameq' option:

ffmpeg uses a fixed default for geometry (-s) and quality (-sameq,
-qscale, -vb etc.). You have to set both explicitly if you need anything
else (which you usually do).

J.
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Old 10-05-2010, 05:15 PM
Celejar
 
Default transcoding flv to mp4

On Tue, 5 Oct 2010 18:58:05 +0200
Jochen Schulz <ml@well-adjusted.de> wrote:

> Celejar:
> >
> > ffmpeg -i example.flv example.mp4
> >
> > I find that the above command line reduces the size of the video to
> > about a third of the original, but at the cost of egregious degradation
> > of the video quality. If I use the 'sameq' option:
>
> ffmpeg uses a fixed default for geometry (-s) and quality (-sameq,
> -qscale, -vb etc.). You have to set both explicitly if you need anything
> else (which you usually do).

Thanks. Is there a tutorial for simple transcoding that you can
recommend? I don't have the time or interest for anything fancy, just
basic transcoding between formats, preserving as much of the quality of
the original as possible.

And shouldn't there be a simple switch or option that does pretty much
that, i.e., "change the format, but keep the size and quality as close
as possible to the original"?

And why on earth is the default behavior to multiply the size by a
factor of four just to retain the same quality? Is mp4 really such an
inferior format to flv that this is required to retain the level of
quality?

Apologies in advance if these are naive questions, but I know little
about this, and transcoding seems to be a sufficiently complex and
arcane subject that simple web searching will only take one so far.

Celejar
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Old 10-05-2010, 08:11 PM
Jochen Schulz
 
Default transcoding flv to mp4

Celejar:
> On Tue, 5 Oct 2010 18:58:05 +0200
> Jochen Schulz <ml@well-adjusted.de> wrote:
>>
>> ffmpeg uses a fixed default for geometry (-s) and quality (-sameq,
>> -qscale, -vb etc.). You have to set both explicitly if you need anything
>> else (which you usually do).
>
> Thanks. Is there a tutorial for simple transcoding that you can
> recommend?

Unfortunately, no. My experience (limited to transcoding DVD material)
is that there is no single command line that delivers a good
quality/time trade-off for all input files.

> I don't have the time or interest for anything fancy, just
> basic transcoding between formats, preserving as much of the quality of
> the original as possible.

Check out Handbrake. It lets you choose from sensible presets, IIRC.

> And shouldn't there be a simple switch or option that does pretty much
> that, i.e., "change the format, but keep the size and quality as close
> as possible to the original"?
>
> And why on earth is the default behavior to multiply the size by a
> factor of four just to retain the same quality? Is mp4 really such an
> inferior format to flv that this is required to retain the level of
> quality?

No, but encoding from one lossy format to another with as little loss as
possible is a task quite hard. In my opinion, -sameq has little or no
use for real-life usage. Use qscale or something like that and see what
you get.

> Apologies in advance if these are naive questions, but I know little
> about this, and transcoding seems to be a sufficiently complex and
> arcane subject that simple web searching will only take one so far.

Your impression matches mine.

J.
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