[mythtv-users] slightly OT: Can dd not be used on mp4?

[Jim Stichnoth]

On Fri, Sep 20, 2013 at 8:58 PM, Ian Evans <dheianevans at gmail.com> wrote:

> On Fri, Sep 20, 2013 at 9:45 PM, Jean-Yves Avenard <jyavenard at gmail.com>wrote:
>
>> On 21 September 2013 11:41, Ian Evans <dheianevans at gmail.com> wrote:
>>
>> >
>> > Worked like a charm.
>> >
>>
>> but now, that's not the same file, mythcommflag may have no issue with
>> that one
>
>
> That's true. Is there any way then to debug why mythcommflag doesn't work
> on the original mp4?
>
> I've looked at the sample you sent me.  (And BTW, if I ask you for the
full recording, it's only because I want to learn more about cassowaries.
:)  )

For reasons beyond my understanding, the MythTV player (which is used for
mythcommflag) doesn't try to deal with "NAL units" in keyframe detection
(see
https://github.com/MythTV/mythtv/blob/master/mythtv/libs/libmythtv/avformatdecoder.cpp#L3126),
so for videos encoded this way, it will fail to find any keyframes.  I'm
not familiar with Handbrake, but perhaps there's a setting that would steer
it away from "NAL unit" and toward "Annex B".

With that said, this kind of file should not require a seektable for
seeking or for duration display.  Your 3-minute sample plays and seeks
perfectly on my system.  So I'm thinking that maybe you have extra markup
in the database from the original recording file.

Try copying the file from that 3-minute sample, or from the original
recording, into your Video Gallery directory, then do a rescan from the
Video Gallery, and see if the file plays correctly.  If it does, this
suggests incorrect markup for the recording.  "mythutil --clearseektable
--chanid xxx --starttime yyy" doesn't currently clear this particularly
markup, so to continue testing, one would need to directly execute a DB
query to clear the extra markup.

Jim
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