[FFmpeg-devel] [PATCH v3 1/2] lavc/ccaption_dec: do not ignore repeated character commands
Aman Gupta
aman at tmm1.net
Tue Apr 19 19:04:48 CEST 2016
This is a tricky one.. I tried your sample in VLC, and it has the same
issue as the latest version of ffmpeg.
The previous behavior of ffmpeg can be restored with the following patch:
diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
index 3b15149..9eff843 100644
--- a/libavcodec/ccaption_dec.c
+++ b/libavcodec/ccaption_dec.c
@@ -712,7 +712,6 @@ static void process_cc608(CCaptionSubContext *ctx,
int64_t pts, uint8_t hi, uint
} else if (hi >= 0x20) {
/* Standard characters (always in pairs) */
handle_char(ctx, hi, lo, pts);
- ctx->prev_cmd[0] = ctx->prev_cmd[1] = 0;
} else {
/* Ignoring all other non data code */
ff_dlog(ctx, "Unknown command 0x%hhx 0x%hhx\n", hi, lo);
However, I've encountered a number of samples where the same character is
legitimately repeated and is not supposed to be skipped.
For instance, the samples on
http://hackipedia.org/ATSC/EIA-608%20samples/EIA-608%20character%20set%20test/
(https://www.youtube.com/watch?v=8TZLxPdC3hk) repeat the character "."
multiple times to show correct spacing.
Similarly, there are an endless number of words in the english language
with repeated characters, such as "ss" in endless and "rr" in correct.
It is unclear to me how the decoder is supposed to distinguish between
characters that are meant to be displayed twice, vs streams that repeat
every ascii character unconditionally.
Further, in your sample it appears that every command is repeated not twice
(as is common in many streams for special character sets and other command,
see
http://hackipedia.org/ATSC/EIA-608%20samples/EIA-608%20character%20set%20test/README.TXT),
but three times.
Aman
On Mon, Apr 18, 2016 at 1:01 PM, Aman Gupta <aman at tmm1.net> wrote:
> Please send me the sample and I will try to fix the issue.
>
> Aman
>
> On Mon, Apr 18, 2016 at 1:22 PM Thierry Foucu <tfoucu at gmail.com> wrote:
>
>> Hi all
>>
>> On Sun, Feb 14, 2016 at 6:11 PM, Aman Gupta <ffmpeg at tmm1.net> wrote:
>>
>>> From: Aman Gupta <aman at tmm1.net>
>>>
>>> control codes in a cc stream can be repeated, and must be ignored.
>>> however, repeated characters must not be ignored. the code attempted to
>>> wipe prev_cmd in handle_char to allow repeated characters to be
>>> processed, but prev_cmd would previously get reset _after_ handle_char()
>>>
>>> i also moved the prev_cmd reset out from handle_char() so it can be
>>> re-used for special character sets, which _must_ be ignored when
>>> repeated.
>>> ---
>>> libavcodec/ccaption_dec.c | 19 ++++++++++---------
>>> 1 file changed, 10 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
>>> index 790f071..5fb2ec6 100644
>>> --- a/libavcodec/ccaption_dec.c
>>> +++ b/libavcodec/ccaption_dec.c
>>> @@ -484,9 +484,6 @@ static void handle_char(CCaptionSubContext *ctx,
>>> char hi, char lo, int64_t pts)
>>> if (ctx->mode != CCMODE_POPON)
>>> ctx->screen_touched = 1;
>>>
>>> - /* reset prev command since character can repeat */
>>> - ctx->prev_cmd[0] = 0;
>>> - ctx->prev_cmd[1] = 0;
>>> if (lo)
>>> ff_dlog(ctx, "(%c,%c)\n", hi, lo);
>>> else
>>> @@ -497,8 +494,15 @@ static void process_cc608(CCaptionSubContext *ctx,
>>> int64_t pts, uint8_t hi, uint
>>> {
>>> if (hi == ctx->prev_cmd[0] && lo == ctx->prev_cmd[1]) {
>>> /* ignore redundant command */
>>> - } else if ( (hi == 0x10 && (lo >= 0x40 && lo <= 0x5f)) ||
>>> - ( (hi >= 0x11 && hi <= 0x17) && (lo >= 0x40 && lo <=
>>> 0x7f) ) ) {
>>> + return;
>>> + }
>>> +
>>> + /* set prev command */
>>> + ctx->prev_cmd[0] = hi;
>>> + ctx->prev_cmd[1] = lo;
>>> +
>>> + if ( (hi == 0x10 && (lo >= 0x40 && lo <= 0x5f)) ||
>>> + ( (hi >= 0x11 && hi <= 0x17) && (lo >= 0x40 && lo <= 0x7f) ) ) {
>>> handle_pac(ctx, hi, lo);
>>> } else if ( ( hi == 0x11 && lo >= 0x20 && lo <= 0x2f ) ||
>>> ( hi == 0x17 && lo >= 0x2e && lo <= 0x2f) ) {
>>> @@ -559,14 +563,11 @@ static void process_cc608(CCaptionSubContext *ctx,
>>> int64_t pts, uint8_t hi, uint
>>> } else if (hi >= 0x20) {
>>> /* Standard characters (always in pairs) */
>>> handle_char(ctx, hi, lo, pts);
>>> + ctx->prev_cmd[0] = ctx->prev_cmd[1] = 0;
>>> } else {
>>> /* Ignoring all other non data code */
>>> ff_dlog(ctx, "Unknown command 0x%hhx 0x%hhx\n", hi, lo);
>>> }
>>> -
>>> - /* set prev command */
>>> - ctx->prev_cmd[0] = hi;
>>> - ctx->prev_cmd[1] = lo;
>>> }
>>>
>>> static int decode(AVCodecContext *avctx, void *data, int *got_sub,
>>> AVPacket *avpkt)
>>> --
>>> 2.5.3
>>>
>>>
>> This commit seems to break some US broadcast CC decoding. (I can provide
>> a 15MB sample file if needed)
>>
>> Before this commit:
>> ffmpeg -f lavfi -i "movie=IhedxzUUxNo.ts[out0+subcc]" -map s "ts.srt"
>> cat ts.srt
>> 1
>> 00:00:01,035 --> 00:00:02,035
>> <font face="Monospace">FAR-RANGING IMPACT PLACES IN THE</font>
>>
>> 2
>> 00:00:02,036 --> 00:00:04,466
>> <font face="Monospace">FAR-RANGING IMPACT PLACES IN THE
>> CHURCH AND AT THE LEVEL OF</font>
>>
>> 3
>> 00:00:04,471 --> 00:00:06,811
>> <font face="Monospace">CHURCH AND AT THE LEVEL OF
>> POLICY ALL ACROSS THE GLOBE.</font>
>>
>> 4
>> 00:00:06,807 --> 00:00:08,537
>> <font face="Monospace">POLICY ALL ACROSS THE GLOBE.
>> CERTAINLY IN THE AREA OF</font>
>>
>> 5
>> 00:00:08,542 --> 00:00:10,382
>> <font face="Monospace">CERTAINLY IN THE AREA OF
>> PASTORAL CARE, I HOPE THAT IT</font>
>>
>> 6
>> 00:00:10,377 --> 00:00:14,677
>> <font face="Monospace">PASTORAL CARE, I HOPE THAT IT
>> WILL LEAD TO LESS DOGMATICTI</font>
>>
>> 7
>> 00:00:14,682 --> 00:00:16,352
>> <font face="Monospace">WILL LEAD TO LESS DOGMATICTI
>> INTERACTION WITH PEOPLE ACROSS A</font>
>>
>> 8
>> 00:00:16,350 --> 00:00:16,920
>> <font face="Monospace">INTERACTION WITH PEOPLE ACROSS A
>> THE BOARD.</font>
>>
>> 9
>> 00:00:16,917 --> 00:00:18,287
>> <font face="Monospace">THE BOARD.
>> I HOPE THAT, YOU KNOW, THERE'S</font>
>>
>> 10
>> 00:00:18,285 --> 00:00:20,785
>> <font face="Monospace">I HOPE THAT, YOU KNOW, THERE'S
>> MORE OF A SENSE THAT THE CHURCH</font>
>>
>>
>>
>> After that commit,
>> cat ts.srt
>> 1
>> 00:00:01,035 --> 00:00:02,035
>> <font face="Monospace">FFFARARAR-R-R-RANANANGIGIGINGNGN</font>
>>
>> 2
>> 00:00:02,036 --> 00:00:04,466
>> <font face="Monospace">FFFARARAR-R-R-RANANANGIGIGINGNGN
>> CCCHUHUHURCRCRCHHH A A ANNND D D</font>
>>
>> 3
>> 00:00:04,471 --> 00:00:06,811
>> <font face="Monospace">CCCHUHUHURCRCRCHHH A A ANNND D D
>> POPOPOLILILICYCYCY A A ALLLL L L</font>
>>
>> 4
>> 00:00:06,807 --> 00:00:08,537
>> <font face="Monospace">POPOPOLILILICYCYCY A A ALLLL L L
>> CCCERERERTATATAINININLYLYLY I I </font>
>>
>> 5
>> 00:00:08,542 --> 00:00:10,382
>> <font face="Monospace">CCCERERERTATATAINININLYLYLY I I
>> PAPAPASSSTOTOTORARARALLL C C CAA</font>
>>
>> 6
>> 00:00:10,377 --> 00:00:14,677
>> <font face="Monospace">PAPAPASSSTOTOTORARARALLL C C CAA
>> WIWIWILLLLLL LELELEADADAD TO</font>
>>
>> 7
>> 00:00:14,682 --> 00:00:16,352
>> <font face="Monospace">WIWIWILLLLLL LELELEADADAD TO
>> INININTETETERARARACTCTCTIOIOION </font>
>>
>> 8
>> 00:00:16,350 --> 00:00:16,920
>> <font face="Monospace">INININTETETERARARACTCTCTIOIOION
>> THTHTHE E E BOBOBOAAARDRDRD...</font>
>>
>> 9
>> 00:00:16,917 --> 00:00:18,287
>> <font face="Monospace">THTHTHE E E BOBOBOAAARDRDRD...
>> I I I HHHOPOPOPEEE T T THHHATATA</font>
>>
>> 10
>> 00:00:18,285 --> 00:00:20,785
>> <font face="Monospace">I I I HHHOPOPOPEEE T T THHHATATA
>> MOMOMORRRE E E OFOFOF A A A SE</font>
>>
>>
>>
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>>
>>
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