Mailing List Archive

Preview image is only 1 pixel
I'm having trouble getting good PNG preview images for NTSC recordings.
The preview PNG images that I get for ATSC recordings are good but the
NTSC previews are on 1 pixel in size. The first problem seemed to be
that mythtv was looking for ImageMagick to create the PNG files. I
installed ImageMagick on my mythbuntu backend but that didn't seem to help.

Any suggestions on how to fix this?

John
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Re: Preview image is only 1 pixel [ In reply to ]
On 01/13/2009 08:41 PM, John Finlay wrote:
> I'm having trouble getting good PNG preview images for NTSC recordings.
> The preview PNG images that I get for ATSC recordings are good but the
> NTSC previews are on 1 pixel in size.

Are you using a frame grabber/software encoder? Are the affected
recordings NUV's (versus MPEG files)?

> The first problem seemed to be
> that mythtv was looking for ImageMagick to create the PNG files.

Shouldn't be. Something else, perhaps? I think the only part of Myth
that uses ImageMagic is the mythcommflag analyze testing tool (that only
a dev is likely to ever use).

Mike
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Re: Preview image is only 1 pixel [ In reply to ]
Michael T. Dean wrote:
> On 01/13/2009 08:41 PM, John Finlay wrote:
>
>> I'm having trouble getting good PNG preview images for NTSC recordings.
>> The preview PNG images that I get for ATSC recordings are good but the
>> NTSC previews are on 1 pixel in size.
>>
>
> Are you using a frame grabber/software encoder? Are the affected
> recordings NUV's (versus MPEG files)?
>
>
Yes I'm using a pchdtv hd-5500 which uses a software encoder for ntsc.
The ntsc recordings are stored as NUV files.

John
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Re: Preview image is only 1 pixel [ In reply to ]
On 01/13/2009 09:28 PM, John Finlay wrote:
> Michael T. Dean wrote:
>
>> On 01/13/2009 08:41 PM, John Finlay wrote:
>>
>>> I'm having trouble getting good PNG preview images for NTSC recordings.
>>> The preview PNG images that I get for ATSC recordings are good but the
>>> NTSC previews are on 1 pixel in size.
>> Are you using a frame grabber/software encoder? Are the affected
>> recordings NUV's (versus MPEG files)?
> Yes I'm using a pchdtv hd-5500 which uses a software encoder for ntsc.
> The ntsc recordings are stored as NUV files.

There was (is?) a bug that causes previews from NUV files (at least
those created when recording--don't know if it affects NUV files created
from transcoding) to be solid color/a single pixel from the upper left
corner of the screen. I can't remember any search terms right now, so I
haven't found the discussion (which, IIRC, included a picture of MythWeb
showing the solid-color previews) about it.

Mike
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Re: Preview image is only 1 pixel [ In reply to ]
On 01/13/2009 09:53 PM, Michael T. Dean wrote:
> On 01/13/2009 09:28 PM, John Finlay wrote:
>
>> Michael T. Dean wrote:
>>
>>> On 01/13/2009 08:41 PM, John Finlay wrote:
>>>
>>>> I'm having trouble getting good PNG preview images for NTSC recordings.
>>>> The preview PNG images that I get for ATSC recordings are good but the
>>>> NTSC previews are on 1 pixel in size.
>>>>
>>> Are you using a frame grabber/software encoder? Are the affected
>>> recordings NUV's (versus MPEG files)?
>>>
>> Yes I'm using a pchdtv hd-5500 which uses a software encoder for ntsc.
>> The ntsc recordings are stored as NUV files.
>>
> There was (is?) a bug that causes previews from NUV files (at least
> those created when recording--don't know if it affects NUV files created
> from transcoding) to be solid color/a single pixel from the upper left
> corner of the screen. I can't remember any search terms right now, so I
> haven't found the discussion (which, IIRC, included a picture of MythWeb
> showing the solid-color previews) about it.

Heh... Turns out that "preview" and "MythWeb" were the search terms I
needed. Here are all the threads, but the disappointing thing is that
there was no resolution:
http://www.gossamer-threads.com/lists/engine?list=mythtv&do=search_results&search_forum=all&search_string=Preview+Images+all+blank+in+MythTV+v0.21+&search_type=AND&search_fields=sb&search_time=&search_user_username=&sb=score&mh=25

Mike
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Re: Preview image is only 1 pixel [ In reply to ]
Michael T. Dean wrote:
> On 01/13/2009 09:53 PM, Michael T. Dean wrote:
>
>> On 01/13/2009 09:28 PM, John Finlay wrote:
>>
>>
>>> Michael T. Dean wrote:
>>>
>>>
>>>> On 01/13/2009 08:41 PM, John Finlay wrote:
>>>>
>>>>
>>>>> I'm having trouble getting good PNG preview images for NTSC recordings.
>>>>> The preview PNG images that I get for ATSC recordings are good but the
>>>>> NTSC previews are on 1 pixel in size.
>>>>>
>>>>>
>>>> Are you using a frame grabber/software encoder? Are the affected
>>>> recordings NUV's (versus MPEG files)?
>>>>
>>>>
>>> Yes I'm using a pchdtv hd-5500 which uses a software encoder for ntsc.
>>> The ntsc recordings are stored as NUV files.
>>>
>>>
>> There was (is?) a bug that causes previews from NUV files (at least
>> those created when recording--don't know if it affects NUV files created
>> from transcoding) to be solid color/a single pixel from the upper left
>> corner of the screen. I can't remember any search terms right now, so I
>> haven't found the discussion (which, IIRC, included a picture of MythWeb
>> showing the solid-color previews) about it.
>>
>
> Heh... Turns out that "preview" and "MythWeb" were the search terms I
> needed. Here are all the threads, but the disappointing thing is that
> there was no resolution:
> http://www.gossamer-threads.com/lists/engine?list=mythtv&do=search_results&search_forum=all&search_string=Preview+Images+all+blank+in+MythTV+v0.21+&search_type=AND&search_fields=sb&search_time=&search_user_username=&sb=score&mh=25
>
> Mike
>
I found a thread in the ubuntu forums that discusses the same problem I
have - unusable 1x1 pixel preview image created for RTjpeg NUV files but
usaable preview image after transcoding to MPEG4 NUV file.

http://ubuntuforums.org/archive/index.php/t-954500.html

John
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Re: Preview image is only 1 pixel [ In reply to ]
On 01/14/2009 04:15 AM, John Finlay wrote:
> I found a thread in the ubuntu forums that discusses the same problem I
> have - unusable 1x1 pixel preview image created for RTjpeg NUV files but
> usaable preview image after transcoding to MPEG4 NUV file.
>
> http://ubuntuforums.org/archive/index.php/t-954500.html

If you're able to track down the bug, we'd love a patch. Not too many
people are using RTJPEG/NUV these days, so it's been very low priority.

Mike
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Re: Preview image is only 1 pixel [ In reply to ]
Michael T. Dean wrote:
> On 01/14/2009 04:15 AM, John Finlay wrote:
>
>> I found a thread in the ubuntu forums that discusses the same problem I
>> have - unusable 1x1 pixel preview image created for RTjpeg NUV files but
>> usaable preview image after transcoding to MPEG4 NUV file.
>>
>> http://ubuntuforums.org/archive/index.php/t-954500.html
>>
>
> If you're able to track down the bug, we'd love a patch. Not too many
> people are using RTJPEG/NUV these days, so it's been very low priority.
>
It's surprising that it is the default encoding in the recording
profiles. I only recently started recording analog so haven't checked
all the nooks and crannies yet. Does MPEG4 require a lot more processing
power from a software encoder? I don't want to overload my BE.

John
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Re: Preview image is only 1 pixel [ In reply to ]
2009/1/14 John Finlay <finlay@moeraki.com>:
> Michael T. Dean wrote:
>> On 01/14/2009 04:15 AM, John Finlay wrote:
>>
>>> I found a thread in the ubuntu forums that discusses the same problem I
>>> have - unusable 1x1 pixel preview image created for RTjpeg NUV files but
>>> usaable preview image after transcoding to MPEG4 NUV file.
>>>
>>> http://ubuntuforums.org/archive/index.php/t-954500.html
>>>
>>
>> If you're able to track down the bug, we'd love a patch. Not too many
>> people are using RTJPEG/NUV these days, so it's been very low priority.
>>
> It's surprising that it is the default encoding in the recording
> profiles. I only recently started recording analog so haven't checked
> all the nooks and crannies yet. Does MPEG4 require a lot more processing
> power from a software encoder? I don't want to overload my BE.

RTJPEG is very lean in terms of CPU usage, whereas MPEG4 is very
heavy. In some cases it is possible to realtime encode MPEG4, but in
most cases it would tie up almost 100% CPU usage on a single stream.

I believe the suggested method was to record in RTJPEG, then
auto-transcode to MPEG4 (at a nice, high nice number to make it a low
priority).

Both are so rarely used these days as most preferred input methods
(HDHomeRun, DVB, ATSC, ClearQAM, IVTV, IPTV) all use either hardware
encoding, or pre-encoded streams, meaning the compression that has to
be done by the backend is essentially zero.

I believe the best way to describe analog capture in Myth is
"Deprecated, but supported".
--
Robert "Anaerin" Johnston
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