Correct visual bugs for video transcoding (preview) and video image snapshoting

[hdsdi3g]

• [x] Inject correct resize for aspect ratio.
• [x] Detect & deinterlace if needed. Do it only for valid broadcast resolution. Add interlace type in summary informations.
• [x] Detect & crop VBI if needed.
• [x] Adjust the time position of the first image relative to the duration of the media.
• [x] Replace in code "snapshoot" word by "snapshot".

[hdsdi3g]

Method for set correct width

 -vf scale=w=in_w*sar:h=in_h

Method for get interlacing (analysing):

 ffmpeg -i $inputfile -filter:v idet -frames:v 1000 -an -f rawvideo -y /dev/null

It return:

[lot of garbage]
[Parsed_idet_0 @ 0x7f8509500000] Single frame detection: TFF:769 BFF:0 Progressive:20 Undetermined:184
[Parsed_idet_0 @ 0x7f8509500000] Multi frame detection: TFF:973 BFF:0 Progressive:0 Undetermined:0

for top field first interlacing, or

[lot of garbage]
[Parsed_idet_0 @ 0x7f9b6af02840] Single frame detection: TFF:163 BFF:77 Progressive:574 Undetermined:167
[Parsed_idet_0 @ 0x7f9b6af02840] Multi frame detection: TFF:175 BFF:126 Progressive:680 Undetermined:0

for an mix with interlacing and progressive, or

[lot of garbage]
[Parsed_idet_0 @ 0x7f84b2e00380] Single frame detection: TFF:36 BFF:53 Progressive:114 Undetermined:798
[Parsed_idet_0 @ 0x7f84b2e00380] Multi frame detection: TFF:0 BFF:382 Progressive:619 Undetermined:0

for a strong mix.