[FFmpeg-devel] [PATCH 1/3] doc/examples/transcode: set packet timebase for decoding

[FFmpeg-devel] [PATCH 1/3] doc/examples/transcode: set packet timebase for decoding

[Anton Khirnov]

It is recommended for callers to set it, though not required.
---
 doc/examples/transcode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/doc/examples/transcode.c b/doc/examples/transcode.c
index 805a028ed7..7110816fe6 100644
--- a/doc/examples/transcode.c
+++ b/doc/examples/transcode.c
@@ -97,6 +97,9 @@ static int open_input_file(const char *filename)
                    "for stream #%u\n", i);
             return ret;
         }
+
+        codec_ctx->pkt_timebase = stream->time_base;
+
         /* Reencode video & audio and remux subtitles etc. */
         if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO
                 || codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
-- 
2.40.1

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[FFmpeg-devel] [PATCH 2/3] doc/examples/transcode: stop using decoder's AVCodecContext.time_base

[Anton Khirnov]

The contents of this field are not defined for decoding. Use
pkt_timebase, which is the timebase of demuxed packets.

Drop a tautological av_packet_rescale_ts() call, as the stream and
decoder timebases are the same.
---
 doc/examples/transcode.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/doc/examples/transcode.c b/doc/examples/transcode.c
index 7110816fe6..2e1491f432 100644
--- a/doc/examples/transcode.c
+++ b/doc/examples/transcode.c
@@ -269,7 +269,7 @@ static int init_filter(FilteringContext* fctx, AVCodecContext *dec_ctx,
         snprintf(args, sizeof(args),
                 "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
                 dec_ctx->width, dec_ctx->height, dec_ctx->pix_fmt,
-                dec_ctx->time_base.num, dec_ctx->time_base.den,
+                dec_ctx->pkt_timebase.num, dec_ctx->pkt_timebase.den,
                 dec_ctx->sample_aspect_ratio.num,
                 dec_ctx->sample_aspect_ratio.den);
 
@@ -309,7 +309,7 @@ static int init_filter(FilteringContext* fctx, AVCodecContext *dec_ctx,
         av_channel_layout_describe(&dec_ctx->ch_layout, buf, sizeof(buf));
         snprintf(args, sizeof(args),
                 "time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=%s",
-                dec_ctx->time_base.num, dec_ctx->time_base.den, dec_ctx->sample_rate,
+                dec_ctx->pkt_timebase.num, dec_ctx->pkt_timebase.den, dec_ctx->sample_rate,
                 av_get_sample_fmt_name(dec_ctx->sample_fmt),
                 buf);
         ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
@@ -547,9 +547,6 @@ int main(int argc, char **argv)
 
             av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the frame\n");
 
-            av_packet_rescale_ts(packet,
-                                 ifmt_ctx->streams[stream_index]->time_base,
-                                 stream->dec_ctx->time_base);
             ret = avcodec_send_packet(stream->dec_ctx, packet);
             if (ret < 0) {
                 av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
-- 
2.40.1

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Re: [FFmpeg-devel] [PATCH 2/3] doc/examples/transcode: stop using decoder's AVCodecContext.time_base

[Paul B Mahol]

LGTM
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[FFmpeg-devel] [PATCH 3/3] doc/examples/transcode: convert timestamps between filtering and encoding

[Anton Khirnov]

The timebases do not have to match.
---
 doc/examples/transcode.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/doc/examples/transcode.c b/doc/examples/transcode.c
index 2e1491f432..ebe5ad2a42 100644
--- a/doc/examples/transcode.c
+++ b/doc/examples/transcode.c
@@ -439,6 +439,10 @@ static int encode_write_frame(unsigned int stream_index, int flush)
     /* encode filtered frame */
     av_packet_unref(enc_pkt);
 
+    if (filt_frame && filt_frame->pts != AV_NOPTS_VALUE)
+        filt_frame->pts = av_rescale_q(filt_frame->pts, filt_frame->time_base,
+                                       stream->enc_ctx->time_base);
+
     ret = avcodec_send_frame(stream->enc_ctx, filt_frame);
 
     if (ret < 0)
@@ -493,6 +497,7 @@ static int filter_encode_write_frame(AVFrame *frame, unsigned int stream_index)
             break;
         }
 
+        filter->filtered_frame->time_base = av_buffersink_get_time_base(filter->buffersink_ctx);;
         filter->filtered_frame->pict_type = AV_PICTURE_TYPE_NONE;
         ret = encode_write_frame(stream_index, 0);
         av_frame_unref(filter->filtered_frame);
-- 
2.40.1

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Re: [FFmpeg-devel] [PATCH 3/3] doc/examples/transcode: convert timestamps between filtering and encoding

[Paul B Mahol]

LGTM
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Re: [FFmpeg-devel] [PATCH 1/3] doc/examples/transcode: set packet timebase for decoding

[Paul B Mahol]

LGTM
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Re: [FFmpeg-devel] [PATCH 1/3] doc/examples/transcode: set packet timebase for decoding

[James Almer]

On 5/31/2023 12:32 PM, Anton Khirnov wrote:
> It is recommended for callers to set it, though not required.

Add this comment to the file. It's meant to be an example for library 
users to refer to for their implementations, after all.

> ---
>   doc/examples/transcode.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/doc/examples/transcode.c b/doc/examples/transcode.c
> index 805a028ed7..7110816fe6 100644
> --- a/doc/examples/transcode.c
> +++ b/doc/examples/transcode.c
> @@ -97,6 +97,9 @@ static int open_input_file(const char *filename)
>                      "for stream #%u\n", i);
>               return ret;
>           }
> +
> +        codec_ctx->pkt_timebase = stream->time_base;
> +
>           /* Reencode video & audio and remux subtitles etc. */
>           if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO
>                   || codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
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Re: [FFmpeg-devel] [PATCH 1/3] doc/examples/transcode: set packet timebase for decoding

[Stefano Sabatini]

On date Wednesday 2023-05-31 16:02:13 -0300, James Almer wrote:
> On 5/31/2023 12:32 PM, Anton Khirnov wrote:
> > It is recommended for callers to set it, though not required.

> Add this comment to the file. It's meant to be an example for library users
> to refer to for their implementations, after all.

I think we should clarify the expectations (I had a similar local
patch to fix this, but I was unsatisfied with the current status quo
and I was exploring if it would be possible to fix this at the library
level - then I was sidetracked).
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