[FFmpeg-devel] [PATCH v6 1/6] ccfifo: Properly handle CEA-708 captions through framerate conversion

[Devin Heitmueller <devin.heitmueller@ltnglobal.com>]

When transcoding video that contains 708 closed captions, the
caption data is tied to the frames as side data.  Simply dropping
or adding frames to change the framerate will result in loss of
data, so the caption data needs to be preserved and reformatted.

For example, without this patch converting 720p59 to 1080i59
would result in loss of 50% of the caption bytes, resulting in
garbled 608 captions and 708 probably wouldn't render at all.
Further, the frames that are there will have an illegal
cc_count for the target framerate, so some decoders may ignore
the packets entirely.

Extract the 608 and 708 tuples and insert them onto queues.  Then
after dropping/adding frames, re-write the tuples back into the
resulting frames at the appropriate rate given the target
framerate.  This includes both having the correct cc_count as
well as clocking out the 608 pairs at the appropriate rate.

Thanks to Lance Wang <lance.lmwang@gmail.com>, Anton
Khirnov <anton@khirnov.net>, and Michael Niedermayer <michael@niedermayer.cc>
for providing review/feedback.

Signed-off-by: Devin Heitmueller <dheitmueller@ltnglobal.com>
---
 libavfilter/Makefile |   1 +
 libavfilter/ccfifo.c | 224 +++++++++++++++++++++++++++++++++++++++++++++++++++
 libavfilter/ccfifo.h | 110 +++++++++++++++++++++++++
 3 files changed, 335 insertions(+)
 create mode 100644 libavfilter/ccfifo.c
 create mode 100644 libavfilter/ccfifo.h

diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 482aeaf..68c8f14 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -14,6 +14,7 @@ OBJS = allfilters.o                                                     \
        buffersink.o                                                     \
        buffersrc.o                                                      \
        colorspace.o                                                     \
+       ccfifo.o                                                         \
        drawutils.o                                                      \
        fifo.o                                                           \
        formats.o                                                        \
diff --git a/libavfilter/ccfifo.c b/libavfilter/ccfifo.c
new file mode 100644
index 0000000..5fb68ce
--- /dev/null
+++ b/libavfilter/ccfifo.c
@@ -0,0 +1,224 @@
+/*
+ * CEA-708 Closed Captioning FIFO
+ * Copyright (c) 2023 LTN Global Communications
+ *
+ * Author: Devin Heitmueller <dheitmueller@ltnglobal.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "ccfifo.h"
+
+struct AVCCFifo {
+    AVFifo *cc_608_fifo;
+    AVFifo *cc_708_fifo;
+    AVRational framerate;
+    int expected_cc_count;
+    int expected_608;
+    int cc_detected;
+    int passthrough;
+    int passthrough_warning;
+    void *log_ctx;
+};
+
+#define MAX_CC_ELEMENTS 128
+#define CC_BYTES_PER_ENTRY 3
+
+struct cc_lookup {
+    int num;
+    int den;
+    int cc_count;
+    int num_608;
+};
+
+const static struct cc_lookup cc_lookup_vals[] = {
+    { 15, 1, 40, 4 },
+    { 24, 1, 25, 3 },
+    { 24000, 1001, 25, 3 },
+    { 30, 1, 20, 2 },
+    { 30000, 1001, 20, 2},
+    { 60, 1, 10, 1 },
+    { 60000, 1001, 10, 1},
+};
+
+void ff_ccfifo_freep(AVCCFifo **ccf)
+{
+    AVCCFifo *tmp = *ccf;
+    if (tmp) {
+        av_fifo_freep2(&tmp->cc_608_fifo);
+        av_fifo_freep2(&tmp->cc_708_fifo);
+    }
+    av_freep(ccf);
+}
+
+AVCCFifo *ff_ccfifo_alloc(AVRational framerate, void *log_ctx)
+{
+    AVCCFifo *ccf;
+    int i;
+
+    ccf = av_mallocz(sizeof(*ccf));
+    if (!ccf)
+        return NULL;
+
+    ccf->log_ctx = log_ctx;
+    ccf->framerate = framerate;
+
+    if (!(ccf->cc_708_fifo = av_fifo_alloc2(MAX_CC_ELEMENTS, CC_BYTES_PER_ENTRY, 0)))
+        goto error;
+
+    if (!(ccf->cc_608_fifo = av_fifo_alloc2(MAX_CC_ELEMENTS, CC_BYTES_PER_ENTRY, 0)))
+        goto error;
+
+    /* Based on the target FPS, figure out the expected cc_count and number of
+       608 tuples per packet.  See ANSI/CTA-708-E Sec 4.3.6.1. */
+    for (i = 0; i < FF_ARRAY_ELEMS(cc_lookup_vals); i++) {
+        if (framerate.num == cc_lookup_vals[i].num &&
+            framerate.den == cc_lookup_vals[i].den) {
+            ccf->expected_cc_count = cc_lookup_vals[i].cc_count;
+            ccf->expected_608 = cc_lookup_vals[i].num_608;
+            break;
+        }
+    }
+
+    if (ccf->expected_608 == 0) {
+        /* We didn't find an output frame we support.  We'll let the call succeed
+           and the FIFO to be allocated, but the extract/inject functions will simply
+           leave everything the way it is */
+        ccf->passthrough = 1;
+    }
+
+    return ccf;
+
+error:
+    ff_ccfifo_freep(&ccf);
+    return NULL;
+}
+
+int ff_ccfifo_getoutputsize(AVCCFifo *ccf)
+{
+    return ccf->expected_cc_count * CC_BYTES_PER_ENTRY;
+}
+
+int ff_ccfifo_ccdetected(AVCCFifo *ccf)
+{
+    return ccf->cc_detected;
+}
+
+int ff_ccfifo_injectbytes(AVCCFifo *ccf, uint8_t *cc_data, size_t len)
+{
+    int cc_608_tuples = 0;
+    int cc_708_tuples = 0;
+    int cc_filled = 0;
+
+    if (ccf->passthrough) {
+        return 0;
+    }
+
+    if (len < ff_ccfifo_getoutputsize(ccf)) {
+        return AVERROR(EINVAL);
+    }
+
+    /* Insert any available data from the 608 FIFO */
+    if (ccf->expected_608 <= av_fifo_can_read(ccf->cc_608_fifo))
+        cc_608_tuples = ccf->expected_608;
+    else
+        cc_608_tuples = av_fifo_can_read(ccf->cc_608_fifo);
+    av_fifo_read(ccf->cc_608_fifo, cc_data, cc_608_tuples);
+    cc_filled += cc_608_tuples;
+
+    /* Insert any available data from the 708 FIFO */
+    if ((ccf->expected_cc_count - cc_filled) <= av_fifo_can_read(ccf->cc_708_fifo))
+        cc_708_tuples = ccf->expected_cc_count - cc_filled;
+    else
+        cc_708_tuples = av_fifo_can_read(ccf->cc_708_fifo);
+    av_fifo_read(ccf->cc_708_fifo, &cc_data[cc_filled * CC_BYTES_PER_ENTRY], cc_708_tuples);
+    cc_filled += cc_708_tuples;
+
+    /* Insert 708 padding into any remaining fields */
+    while (cc_filled < ccf->expected_cc_count) {
+        cc_data[cc_filled * CC_BYTES_PER_ENTRY]     = 0xfa;
+        cc_data[cc_filled * CC_BYTES_PER_ENTRY + 1] = 0x00;
+        cc_data[cc_filled * CC_BYTES_PER_ENTRY + 2] = 0x00;
+        cc_filled++;
+    }
+
+    return 0;
+}
+
+int ff_ccfifo_inject(AVCCFifo *ccf, AVFrame *frame)
+{
+    AVFrameSideData *sd;
+    int ret;
+
+    if (ccf->passthrough == 1 || ccf->cc_detected == 0)
+        return 0;
+
+    sd = av_frame_new_side_data(frame, AV_FRAME_DATA_A53_CC,
+                                ff_ccfifo_getoutputsize(ccf));
+    if (sd) {
+        ret = ff_ccfifo_injectbytes(ccf, sd->data, sd->size);
+        if (ret < 0) {
+            av_frame_remove_side_data(frame, AV_FRAME_DATA_A53_CC);
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
+int ff_ccfifo_extractbytes(AVCCFifo *ccf, uint8_t *cc_bytes, size_t len)
+{
+    int cc_count = len / CC_BYTES_PER_ENTRY;
+
+    if (ccf->passthrough == 1) {
+        av_log_once(ccf->log_ctx, AV_LOG_WARNING, AV_LOG_DEBUG, &ccf->passthrough_warning,
+                    "cc_fifo cannot transcode captions fps=%d/%d\n",
+                    ccf->framerate.num, ccf->framerate.den);
+        return 0;
+    }
+
+    ccf->cc_detected = 1;
+
+    for (int i = 0; i < cc_count; i++) {
+        /* See ANSI/CTA-708-E Sec 4.3, Table 3 */
+        uint8_t cc_valid = (cc_bytes[CC_BYTES_PER_ENTRY*i] & 0x04) >> 2;
+        uint8_t cc_type = cc_bytes[CC_BYTES_PER_ENTRY*i] & 0x03;
+        if (cc_type == 0x00 || cc_type == 0x01) {
+            av_fifo_write(ccf->cc_608_fifo, &cc_bytes[CC_BYTES_PER_ENTRY*i], 1);
+        } else if (cc_valid && (cc_type == 0x02 || cc_type == 0x03)) {
+            av_fifo_write(ccf->cc_708_fifo, &cc_bytes[CC_BYTES_PER_ENTRY*i], 1);
+        }
+    }
+    return 0;
+}
+
+/* Read the A53 side data, discard padding, and put 608/708 into
+   queues so we can ensure they get into the output frames at
+   the correct rate... */
+int ff_ccfifo_extract(AVCCFifo *ccf, AVFrame *frame)
+{
+    AVFrameSideData *side_data = av_frame_get_side_data(frame, AV_FRAME_DATA_A53_CC);
+    if (side_data) {
+        ff_ccfifo_extractbytes(ccf, side_data->data, side_data->size);
+
+        /* Remove the side data, as we will re-create it on the
+           output as needed */
+        if (!ccf->passthrough)
+            av_frame_remove_side_data(frame, AV_FRAME_DATA_A53_CC);
+    }
+    return 0;
+}
diff --git a/libavfilter/ccfifo.h b/libavfilter/ccfifo.h
new file mode 100644
index 0000000..44c9245
--- /dev/null
+++ b/libavfilter/ccfifo.h
@@ -0,0 +1,110 @@
+/*
+ * CEA-708 Closed Captioning FIFO
+ * Copyright (c) 2023 LTN Global Communications
+ *
+ * Author: Devin Heitmueller <dheitmueller@ltnglobal.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * CC FIFO Buffer
+ */
+
+#ifndef AVFILTER_CCFIFO_H
+#define AVFILTER_CCFIFO_H
+
+#include "libavutil/avutil.h"
+#include "libavutil/frame.h"
+#include "libavutil/fifo.h"
+
+typedef struct AVCCFifo AVCCFifo;
+
+/**
+ * Allocate an AVCCFifo.
+ *
+ * @param framerate   output framerate
+ * @param log_ctx     used for any av_log() calls
+ * @return            newly allocated AVCCFifo, or NULL on error
+ */
+AVCCFifo *ff_ccfifo_alloc(AVRational framerate, void *log_ctx);
+
+/**
+ * Free an AVCCFifo
+ *
+ * @param ccf Pointer to the pointer to the AVCCFifo which should be freed
+ * @note `*ptr = NULL` is safe and leads to no action.
+ */
+void ff_ccfifo_freep(AVCCFifo **ccf);
+
+
+/**
+ * Extract CC data from an AVFrame
+ *
+ * Extract CC bytes from the AVFrame, insert them into our queue, and
+ * remove the side data from the AVFrame.  The side data is removed
+ * as it will be re-inserted at the appropriate rate later in the
+ * filter.
+ *
+ * @param af          AVCCFifo to write to
+ * @param frame       AVFrame with the video frame to operate on
+ * @return            Zero on success, or negative AVERROR
+ *                    code on failure.
+ */
+int ff_ccfifo_extract(AVCCFifo *ccf, AVFrame *frame);
+
+/**
+ *Just like ff_ccfifo_extract(), but takes the raw bytes instead of an AVFrame
+ */
+int ff_ccfifo_extractbytes(AVCCFifo *ccf, uint8_t *data, size_t len);
+
+/**
+ * Provide the size in bytes of an output buffer to allocate
+ *
+ * Ask for how many bytes the output will contain, so the caller can allocate
+ * an appropriately sized buffer and pass it to ff_ccfifo_injectbytes()
+ *
+ */
+int ff_ccfifo_getoutputsize(AVCCFifo *ccf);
+
+/**
+ * Insert CC data from the FIFO into an AVFrame (as side data)
+ *
+ * Dequeue the appropriate number of CC tuples based on the
+ * frame rate, and insert them into the AVFrame
+ *
+ * @param af          AVCCFifo to read from
+ * @param frame       AVFrame with the video frame to operate on
+ * @return            Zero on success, or negative AVERROR
+ *                    code on failure.
+ */
+int ff_ccfifo_inject(AVCCFifo *ccf, AVFrame *frame);
+
+/**
+ * Just like ff_ccfifo_inject(), but takes the raw bytes to insert the CC data
+ * int rather than an AVFrame
+ */
+int ff_ccfifo_injectbytes(AVCCFifo *ccf, uint8_t *data, size_t len);
+
+/**
+ * Returns 1 if captions have been found as a prior call
+ * to ff_ccfifo_extract() or ff_ccfifo_extractbytes()
+ */
+int ff_ccfifo_ccdetected(AVCCFifo *ccf);
+
+#endif /* AVFILTER_CCFIFO_H */
-- 
1.8.3.1

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