[FFmpeg-devel] [PATCH] Add A53 Closed Captions to MPEG header if they are available.
John P Poet
jppoet at gmail.com
Thu Jun 8 00:46:32 EEST 2017
On Tue, Jun 6, 2017 at 4:48 PM John P Poet <jppoet at gmail.com> wrote:
> On Tue, Jun 6, 2017 at 4:40 PM Kieran Kunhya <kierank at obe.tv> wrote:
>> > The cc_count is only 5 bits, which mean that only 31 3-byte "closed
>> > constructs" will fit in a "block". Testing this with 1080i60
>> material, I
>> > found that 2 or 3 blocks was often necessary to hold all of the CC data.
>> > I tried ignoring that limit of 31 "constructs" per block, and ended up
>> > corrupt captions. By preserving the 2 or 3 separate blocks I observed
>> > from the original source, the captions are perfect.
>> Odd, ATSC specifies specific bitrate requirements in this area. Are you
>> sure your insertion process isn't bursting?
> The source is SDI with embedded 708 captions. I supposed there may be an
> issue there. I have not tried this with any other source.
>From my SDI source, most frames have cc_count=20. Then there can be two or
three frames without any CC packets, which are often followed by a single
frame with with two or three VBI lines of CC packets: e.g. two or three
groups of cc_count=20 in a single frame.
When you asked if it is "bursting", I assume this is what you mean? If so,
what would you suggest I do about it?
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