ffmpeg: insert bitmap subtitles as video in filters.

With this feature, it becomes possible to perform commonly
requested tasks, such as hardcoding bitmap subtitles.

This will be reverted once libavfilter has proper support
for subtitles. All the changes have the string "sub2video"
in them, it makes it easy to spot the parts.

Changelog

@@ -39,6 +39,7 @@ version next:
 - concat filter
 - flite filter
 - Canopus Lossless Codec decoder
+- bitmap subtitles in filters (experimental and temporary)
 
 
 version 0.11:

doc/ffmpeg.texi

@@ -989,6 +989,22 @@ ffmpeg -i video.mkv -i image.png -filter_complex 'overlay' out.mkv
 @end example
 @end table
 
+As a special exception, you can use a bitmap subtitle stream as input: it
+will be converted into a video with the same size as the largest video in
+the file, or 720×576 if no video is present. Note that this is an
+experimental and temporary solution. It will be removed once libavfilter has
+proper support for subtitles.
+
+For example, to hardcode subtitles on top of a DVB-T recording stored in
+MPEG-TS format, delaying the subtitles by 1 second:
+@example
+ffmpeg -i input.ts -filter_complex \
+  '[#0x2ef] setpts=PTS+1/TB [sub] ; [#0x2d0] [sub] overlay' \
+  -sn -map '#0x2dc' output.mkv
+@end example
+(0x2d0, 0x2dc and 0x2ef are the MPEG-TS PIDs of respectively the video,
+audio and subtitles streams; 0:0, 0:3 and 0:7 would have worked too)
+
 @section Preset files
 A preset file contains a sequence of @var{option}=@var{value} pairs,
 one for each line, specifying a sequence of options which would be

ffmpeg.c

@@ -249,6 +249,12 @@ typedef struct InputStream {
     int      resample_channels;
     uint64_t resample_channel_layout;
 
+    struct sub2video {
+        int64_t last_pts;
+        AVFilterBufferRef *ref;
+        int w, h;
+    } sub2video;
+
     /* a pool of free buffers for decoded data */
     FrameBuffer *buffer_pool;
     int dr1;
@@ -504,6 +510,155 @@ static void update_benchmark(const char *fmt, ...)
     }
 }
 
+/* sub2video hack:
+   Convert subtitles to video with alpha to insert them in filter graphs.
+   This is a temporary solution until libavfilter gets real subtitles support.
+ */
+
+
+static int sub2video_prepare(InputStream *ist)
+{
+    AVFormatContext *avf = input_files[ist->file_index]->ctx;
+    int i, ret, w, h;
+    uint8_t *image[4];
+    int linesize[4];
+
+    /* Compute the size of the canvas for the subtitles stream.
+       If the subtitles codec has set a size, use it. Otherwise use the
+       maximum dimensions of the video streams in the same file. */
+    w = ist->st->codec->width;
+    h = ist->st->codec->height;
+    if (!(w && h)) {
+        for (i = 0; i < avf->nb_streams; i++) {
+            if (avf->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
+                w = FFMAX(w, avf->streams[i]->codec->width);
+                h = FFMAX(h, avf->streams[i]->codec->height);
+            }
+        }
+        if (!(w && h)) {
+            w = FFMAX(w, 720);
+            h = FFMAX(h, 576);
+        }
+        av_log(avf, AV_LOG_INFO, "sub2video: using %dx%d canvas\n", w, h);
+    }
+    ist->sub2video.w = ist->st->codec->width  = w;
+    ist->sub2video.h = ist->st->codec->height = h;
+
+    /* rectangles are PIX_FMT_PAL8, but we have no guarantee that the
+       palettes for all rectangles are identical or compatible */
+    ist->st->codec->pix_fmt = PIX_FMT_RGB32;
+
+    ret = av_image_alloc(image, linesize, w, h, PIX_FMT_RGB32, 32);
+    if (ret < 0)
+        return ret;
+    memset(image[0], 0, h * linesize[0]);
+    ist->sub2video.ref = avfilter_get_video_buffer_ref_from_arrays(
+            image, linesize, AV_PERM_READ | AV_PERM_PRESERVE,
+            w, h, PIX_FMT_RGB32);
+    if (!ist->sub2video.ref) {
+        av_free(image[0]);
+        return AVERROR(ENOMEM);
+    }
+    return 0;
+}
+
+static void sub2video_copy_rect(uint8_t *dst, int dst_linesize, int w, int h,
+                                AVSubtitleRect *r)
+{
+    uint32_t *pal, *dst2;
+    uint8_t *src, *src2;
+    int x, y;
+
+    if (r->type != SUBTITLE_BITMAP) {
+        av_log(NULL, AV_LOG_WARNING, "sub2video: non-bitmap subtitle\n");
+        return;
+    }
+    if (r->x < 0 || r->x + r->w > w || r->y < 0 || r->y + r->h > h) {
+        av_log(NULL, AV_LOG_WARNING, "sub2video: rectangle overflowing\n");
+        return;
+    }
+
+    dst += r->y * dst_linesize + r->x * 4;
+    src = r->pict.data[0];
+    pal = (uint32_t *)r->pict.data[1];
+    for (y = 0; y < r->h; y++) {
+        dst2 = (uint32_t *)dst;
+        src2 = src;
+        for (x = 0; x < r->w; x++)
+            *(dst2++) = pal[*(src2++)];
+        dst += dst_linesize;
+        src += r->pict.linesize[0];
+    }
+}
+
+static void sub2video_push_ref(InputStream *ist, int64_t pts)
+{
+    AVFilterBufferRef *ref = ist->sub2video.ref;
+    int i;
+
+    ist->sub2video.last_pts = ref->pts = pts;
+    for (i = 0; i < ist->nb_filters; i++)
+        av_buffersrc_add_ref(ist->filters[i]->filter,
+                             avfilter_ref_buffer(ref, ~0),
+                             AV_BUFFERSRC_FLAG_NO_CHECK_FORMAT |
+                             AV_BUFFERSRC_FLAG_NO_COPY);
+}
+
+static void sub2video_update(InputStream *ist, AVSubtitle *sub, int64_t pts)
+{
+    int w = ist->sub2video.w, h = ist->sub2video.h;
+    AVFilterBufferRef *ref = ist->sub2video.ref;
+    int8_t *dst;
+    int     dst_linesize;
+    int i;
+
+    if (!ref)
+        return;
+    dst          = ref->data    [0];
+    dst_linesize = ref->linesize[0];
+    memset(dst, 0, h * dst_linesize);
+    for (i = 0; i < sub->num_rects; i++)
+        sub2video_copy_rect(dst, dst_linesize, w, h, sub->rects[i]);
+    sub2video_push_ref(ist, pts);
+}
+
+static void sub2video_heartbeat(InputStream *ist, int64_t pts)
+{
+    InputFile *infile = input_files[ist->file_index];
+    int i, j, nb_reqs;
+    int64_t pts2;
+
+    /* When a frame is read from a file, examine all sub2video streams in
+       the same file and send the sub2video frame again. Otherwise, decoded
+       video frames could be accumulating in the filter graph while a filter
+       (possibly overlay) is desperately waiting for a subtitle frame. */
+    for (i = 0; i < infile->nb_streams; i++) {
+        InputStream *ist2 = input_streams[infile->ist_index + i];
+        if (!ist2->sub2video.ref)
+            continue;
+        /* subtitles seem to be usually muxed ahead of other streams;
+           if not, substracting a larger time here is necessary */
+        pts2 = av_rescale_q(pts, ist->st->time_base, ist2->st->time_base) - 1;
+        /* do not send the heartbeat frame if the subtitle is already ahead */
+        if (pts2 <= ist2->sub2video.last_pts)
+            continue;
+        for (j = 0, nb_reqs = 0; j < ist2->nb_filters; j++)
+            nb_reqs += av_buffersrc_get_nb_failed_requests(ist2->filters[j]->filter);
+        if (nb_reqs)
+            sub2video_push_ref(ist2, pts2);
+    }
+}
+
+static void sub2video_flush(InputStream *ist)
+{
+    int i;
+
+    for (i = 0; i < ist->nb_filters; i++)
+        av_buffersrc_add_ref(ist->filters[i]->filter, NULL, 0);
+}
+
+/* end of sub2video hack */
+
 static void reset_options(OptionsContext *o, int is_input)
 {
     const OptionDef *po = options;
@@ -745,7 +900,10 @@ static void init_input_filter(FilterGraph *fg, AVFilterInOut *in)
         s = input_files[file_idx]->ctx;
 
         for (i = 0; i < s->nb_streams; i++) {
-            if (s->streams[i]->codec->codec_type != type)
+            enum AVMediaType stream_type = s->streams[i]->codec->codec_type;
+            if (stream_type != type &&
+                !(stream_type == AVMEDIA_TYPE_SUBTITLE &&
+                  type == AVMEDIA_TYPE_VIDEO /* sub2video hack */))
                 continue;
             if (check_stream_specifier(s, s->streams[i], *p == ':' ? p + 1 : p) == 1) {
                 st = s->streams[i];
@@ -1025,6 +1183,12 @@ static int configure_input_video_filter(FilterGraph *fg, InputFilter *ifilter,
     int pad_idx = in->pad_idx;
     int ret;
 
+    if (ist->st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
+        ret = sub2video_prepare(ist);
+        if (ret < 0)
+            return ret;
+    }
+
     sar = ist->st->sample_aspect_ratio.num ?
           ist->st->sample_aspect_ratio :
           ist->st->codec->sample_aspect_ratio;
@@ -1413,6 +1577,7 @@ void av_noreturn exit_program(int ret)
         av_freep(&input_streams[i]->decoded_frame);
         av_dict_free(&input_streams[i]->opts);
         free_buffer_pool(&input_streams[i]->buffer_pool);
+        avfilter_unref_bufferp(&input_streams[i]->sub2video.ref);
         av_freep(&input_streams[i]->filters);
         av_freep(&input_streams[i]);
     }
@@ -2636,13 +2801,16 @@ static int transcode_subtitles(InputStream *ist, AVPacket *pkt, int *got_output)
     AVSubtitle subtitle;
     int i, ret = avcodec_decode_subtitle2(ist->st->codec,
                                           &subtitle, got_output, pkt);
-    if (ret < 0)
-        return ret;
-    if (!*got_output)
+    if (ret < 0 || !*got_output) {
+        if (!pkt->size)
+            sub2video_flush(ist);
         return ret;
+    }
 
     rate_emu_sleep(ist);
 
+    sub2video_update(ist, &subtitle, pkt->pts);
+
     for (i = 0; i < nb_output_streams; i++) {
         OutputStream *ost = output_streams[i];
 
@@ -3847,6 +4015,8 @@ static int transcode(void)
             }
         }
 
+        sub2video_heartbeat(ist, pkt.pts);
+
         // fprintf(stderr,"read #%d.%d size=%d\n", ist->file_index, ist->st->index, pkt.size);
         if ((ret = output_packet(ist, &pkt)) < 0 ||
             ((ret = poll_filters()) < 0 && ret != AVERROR_EOF)) {