[FFmpeg-devel] [PATCH v2] avcodec/libjxldec: emit proper PTS to decoded AVFrame

[Leo Izen <leo.izen@gmail.com>]

If a sequence of JXL images is encapsulated in a container that has PTS
information, we should use the PTS information from the container. At
this time there is no container that does this, but if JPEG XL support
is ever added to NUT, AVTransport, or some other container, this commit
should allow the PTS information those containers provide to work as
expected.

Signed-off-by: Leo Izen <leo.izen@gmail.com>
---
 libavcodec/libjxldec.c | 57 +++++++++++++++++++++---------------------
 1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/libavcodec/libjxldec.c b/libavcodec/libjxldec.c
index 002740d9c1..6e630fb1b0 100644
--- a/libavcodec/libjxldec.c
+++ b/libavcodec/libjxldec.c
@@ -54,10 +54,10 @@ typedef struct LibJxlDecodeContext {
     JxlDecoderStatus events;
     AVBufferRef *iccp;
     AVPacket *avpkt;
-    int64_t pts;
+    int64_t accumulated_pts;
     int64_t frame_duration;
     int prev_is_last;
-    AVRational timebase;
+    AVRational anim_timebase;
     AVFrame *frame;
 } LibJxlDecodeContext;
 
@@ -80,7 +80,6 @@ static int libjxl_init_jxl_decoder(AVCodecContext *avctx)
     memset(&ctx->basic_info, 0, sizeof(JxlBasicInfo));
     memset(&ctx->jxl_pixfmt, 0, sizeof(JxlPixelFormat));
     ctx->prev_is_last = 1;
-    ctx->frame_duration = 1;
 
     return 0;
 }
@@ -104,7 +103,6 @@ static av_cold int libjxl_decode_init(AVCodecContext *avctx)
     }
 
     ctx->avpkt = avctx->internal->in_pkt;
-    ctx->pts = 0;
     ctx->frame = av_frame_alloc();
     if (!ctx->frame)
         return AVERROR(ENOMEM);
@@ -370,12 +368,15 @@ static int libjxl_receive_frame(AVCodecContext *avctx, AVFrame *frame)
 
     while (1) {
         size_t remaining;
+        JxlFrameHeader header;
 
         if (!pkt->size) {
             av_packet_unref(pkt);
             ret = ff_decode_get_packet(avctx, pkt);
             if (ret < 0 && ret != AVERROR_EOF)
                 return ret;
+            ctx->accumulated_pts = 0;
+            ctx->frame_duration = 0;
             if (!pkt->size) {
                 /* jret set by the last iteration of the loop */
                 if (jret == JXL_DEC_NEED_MORE_INPUT) {
@@ -429,12 +430,8 @@ static int libjxl_receive_frame(AVCodecContext *avctx, AVFrame *frame)
             if ((ret = ff_set_dimensions(avctx, ctx->basic_info.xsize, ctx->basic_info.ysize)) < 0)
                 return ret;
             if (ctx->basic_info.have_animation)
-                ctx->timebase = av_make_q(ctx->basic_info.animation.tps_denominator,
-                                          ctx->basic_info.animation.tps_numerator);
-            else if (avctx->pkt_timebase.num)
-                ctx->timebase = avctx->pkt_timebase;
-            else
-                ctx->timebase = AV_TIME_BASE_Q;
+                ctx->anim_timebase = av_make_q(ctx->basic_info.animation.tps_denominator,
+                                               ctx->basic_info.animation.tps_numerator);
             continue;
         case JXL_DEC_COLOR_ENCODING:
             av_log(avctx, AV_LOG_DEBUG, "COLOR_ENCODING event emitted\n");
@@ -462,23 +459,24 @@ static int libjxl_receive_frame(AVCodecContext *avctx, AVFrame *frame)
 #endif
             continue;
         case JXL_DEC_FRAME:
+            /* Frame here refers to the Frame bundle, not a decoded picture */
             av_log(avctx, AV_LOG_DEBUG, "FRAME event emitted\n");
-            if (!ctx->basic_info.have_animation || ctx->prev_is_last) {
+            if (ctx->prev_is_last) {
+                /*
+                 * The last frame sent was tagged as "is_last" which
+                 * means this is a new image file altogether.
+                 */
                 ctx->frame->pict_type = AV_PICTURE_TYPE_I;
                 ctx->frame->flags |= AV_FRAME_FLAG_KEY;
             }
-            if (ctx->basic_info.have_animation) {
-                JxlFrameHeader header;
-                if (JxlDecoderGetFrameHeader(ctx->decoder, &header) != JXL_DEC_SUCCESS) {
-                    av_log(avctx, AV_LOG_ERROR, "Bad libjxl dec frame event\n");
-                    return AVERROR_EXTERNAL;
-                }
-                ctx->prev_is_last = header.is_last;
-                ctx->frame_duration = header.duration;
-            } else {
-                ctx->prev_is_last = 1;
-                ctx->frame_duration = 1;
+            if (JxlDecoderGetFrameHeader(ctx->decoder, &header) != JXL_DEC_SUCCESS) {
+                av_log(avctx, AV_LOG_ERROR, "Bad libjxl dec frame event\n");
+                return AVERROR_EXTERNAL;
             }
+            ctx->prev_is_last = header.is_last;
+            /* zero duration for animation means the frame is not presented */
+            if (ctx->basic_info.have_animation && header.duration)
+                ctx->frame_duration = header.duration;
             continue;
         case JXL_DEC_FULL_IMAGE:
             /* full image is one frame, even if animated */
@@ -490,14 +488,17 @@ static int libjxl_receive_frame(AVCodecContext *avctx, AVFrame *frame)
                 /* ownership is transfered, and it is not ref-ed */
                 ctx->iccp = NULL;
             }
-            if (avctx->pkt_timebase.num) {
-                ctx->frame->pts = av_rescale_q(ctx->pts, ctx->timebase, avctx->pkt_timebase);
-                ctx->frame->duration = av_rescale_q(ctx->frame_duration, ctx->timebase, avctx->pkt_timebase);
+            if (ctx->basic_info.have_animation) {
+                ctx->frame->pts = av_rescale_q(ctx->accumulated_pts, ctx->anim_timebase, avctx->pkt_timebase);
+                ctx->frame->duration = av_rescale_q(ctx->frame_duration, ctx->anim_timebase, avctx->pkt_timebase);
             } else {
-                ctx->frame->pts = ctx->pts;
-                ctx->frame->duration = ctx->frame_duration;
+                ctx->frame->pts = 0;
+                ctx->frame->duration = pkt->duration;
             }
-            ctx->pts += ctx->frame_duration;
+            if (pkt->pts != AV_NOPTS_VALUE)
+                ctx->frame->pts += pkt->pts;
+            ctx->accumulated_pts += ctx->frame_duration;
+            ctx->frame->pkt_dts = pkt->dts;
             av_frame_move_ref(frame, ctx->frame);
             return 0;
         case JXL_DEC_SUCCESS:
-- 
2.43.0

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