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

[Ian Evans]

On Sun, Sep 22, 2013 at 9:41 AM, Jim Stichnoth <stichnot at gmail.com> wrote:

> 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.
> :)  )
>

That made me laugh.


>
> 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".
>

>From a quick glimpse, I couldn't see anything. I'm not married to
Handbrake, so if ffmpeg can do the same task and not use NAL units, I'm
game to try. (Basically the handbrake job vertically/horizontally crops SD
shows broadcast on HD channels, saving a few gigs a show until I can get a
new drive.)


>
> 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.
>

I copied it over to Mythvideo and was able to seek/fast forward.

Thanks for your detective work.
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