======= GSOC 2015 Documentation =======
Technical Documentation
Transport Stream
Data structure in Transport Stream made for Multiprogram.
Decoder
In CCextractor we have single Decoder Initialization function,
struct lib_cc_decode* init_cc_decode (struct ccx_decoders_common_settings_t *setting)
where settings of decoder are passed in its parameter
struct ccx_decoders_common_settings_t {
LLONG subs_delay; // ms to delay (or advance) subsenum ccx_output_format output_format; // What kind of output format should be used?int fix_padding; // Replace 0000 with 8080 in HDTV (needed for some cards)struct ccx_boundary_time extraction_start, extraction_end; // Segment we actually processint cc_to_stdout;int extract; // Extract 1st, 2nd or both fieldsint fullbin; // Disable pruning of padding cc blocksstruct ccx_decoder_608_settings *settings_608; // Contains the settings for the 608 decoder.ccx_decoder_dtvcc_settings_t *settings_dtvcc; //Same for cea 708 captions decoder (dtvcc)int cc_channel; // Channel we want to dump in srt modeunsigned send_to_srv;unsigned int hauppauge_mode; // If 1, use PID=1003, process specially and so onint program_number;enum ccx_code_type codec;void *private_data;
};
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In settings subs\_delay is deprecated and should not be used further,
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subs\_delay parameter was added for transition period and need to be
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removed. same thing for send\_to\_srv, output\_format.
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If Demuxer has already initialized deocder like in case of teletext and
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dvbsub at the time of demuxing then private\_data can be filled with
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context of specific format decoder and initialize value enum
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ccx\_code\_type codec.
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### How to use multiprogram extraction using CCExtractor?
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For Command line user its simply passing -multiprogram argument to
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ccextractor `cextractor -multiprogram `
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### How to use OCR for extracting bitmap subtitle in text format?
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For doing OCR on bitmap image of subtitles, compile code after enabling
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OCR in source code. While compiling ccextractor, follow OCR.txt in doc
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folder of ccextractor source code.
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### Link list data structure in CCextractor
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Background
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----------
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Link List implemented in CCextractor is taken from Linux Source Code.
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Please note ccextractor Link list does not have same syntax as it is in
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linux source code but its similar and only changes that you will in
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CCextractor link list would be adaptation of Windows environment.
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Implementation
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--------------
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For implementing link list you need head of link list using which you
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can always traverse update or delete the complete link list. Keep head
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of link List in safe location, most common mistake developer do is
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keeping head inside node structure and do memory leakage if loosing Head
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of link list.
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for example we need multiple decoders to extract different Subtitles
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from different programs. so as discussed above Head of link list should
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not be kept in Decoder Context. It must be in its parent which cant die
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or deleted before its child. We will keep head of decoder link list in
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CCextractor library Context which contain all demuxer, decoder and
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encoder. Following would be syntax for keeping decoder List in Library
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Context.
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struct lib\_ccx\_ctx {
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` struct list_head dec_ctx_head;`
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}; ~~~
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now next thing to do is initialize the head of link list, for decoder
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link list we would initialize it in initialization part of library
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void init\_libraries(void) {
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` INIT_LIST_HEAD(&ctx->dec_ctx_head);`
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} ~~~
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Now in your decoder context put connector of link list, which will
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actually make your dec\_ctx as node `struct lib_cc_decode` `{`
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`struct list_head list;` `};`
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Put your decoder node back in link list, in below code I have assumed
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that you allocated decoder Context and saved in variable dec\_ctx and
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your library with head of your link list is saved in ctx variable.
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`list_add_tail( &(dec_ctx->list), &(ctx->dec_ctx_head) );`
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One of the reason that people prefer Array because traversing,
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searching, updating and deleting them is very easy, now that excuse wont
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work, Now only reason to use Array would be contiguous memory
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allocation.
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Traversing Link List for searching and updating some parameter
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list\_for\_each\_entry(dec\_ctx, &ctx-\>dec\_ctx\_head, list, struct
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lib\_cc\_decode) {
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` //Access your parameter here`\
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` print(dec_ctx->program_number);`
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} ~~~
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there is different code for traversing link list when you might delete
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complete node of link list while traversing. also mind that delete link
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of node from link list first after then delete or free your memory
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allocated for node list\_for\_each\_entry\_safe(dec\_ctx,
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dec\_ctx1, &lctx-\>dec\_ctx\_head, list, struct lib\_cc\_decode) {
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` list_del(&dec_ctx->list);`\
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` free(dec_ctx);`
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} ~~~
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##### How to evaluate?
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Clone my repository from git hub in **any** directory of gsoc server
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`git clone --depth `[`https://github.com/anshul1912/ccextractor.git`](https://github.com/anshul1912/ccextractor.git)
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Run CCextractor with multiprogram in argument
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -multiprogram -o a.srt`
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In file specified in above command there are 6 program with closed
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caption. but ccextractor tries to extract Closed caption from all 8
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programs therefore it makes 2 empty files. you would have following file
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in directory where command was executed.
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`[anshul@gsocdev linux]$ ls a_*`
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`a_1.srt a_2.srt a_3.srt a_4.srt a_5.srt a_6.srt a_7.srt a_8.srt`
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From same file extract subtitles individually using -pn argument. you
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can use following command to extract each program.
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -pn 1 -o pn_1.srt`
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -pn 2 -o pn_2.srt`
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -pn 3 -o pn_3.srt`
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -pn 4 -o pn_4.srt`
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -pn 5 -o pn_5.srt`
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`ccextractor /repository/newRepository/TestFiles/General/Closedcaption_atsc_multiprog.ts -pn 6 -o pn_6.srt`
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Now check the difference between files generated by ccextractor with
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multiprogram and pn. for example you can use command line tool like
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following. `diff a_1.srt pn_1.srt`
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##### Contribution for blog
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Now CCextractor have feature to extract Closed Caption from all channels
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simultaneously. Its not just about extracting Closed caption from all
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channel but also converting them to desirable format.
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Now there is no need of multiple Capture Device to capture single live
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closed caption. Use this wonderful openSource software and save your
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hard earn money to donate in technology and make this software more
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wonderful.
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This Multiprogram Closed caption Extraction works for DVBSub, Teletext
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and Closed Caption. which means whichever is your country Multi programs
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Extraction would work.
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If in some peoples country multiprogram subtitles extraction is still
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not working, we would say invest here and help this newer
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`generation to do more wonderful and innovative work instead of discovering or inventing Wheel`
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##### Addendum
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= My Graduation would be completed this year, so I would seek the
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opportunity to be mentor or co-mentor in CCExtractor. CCExtractor is
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great tool which can be used for various multimedia application, so my
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development would continue in this project at least till C has its
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charm. Since the part of work that I have done in CCextractor was done
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with atmost care according to my knowledge, therefore I would try to
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remove any bug in part of my code reported by someone else or
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encountered by me.
not set