The for-loop and the warning are copied from somewhere else in the decoder. I'm
also quite sure that it cannot really happen.
One cannot set the option to discard old frames and also try to seek. I did not
manage to create an example with calls to switch_root while reading from a
file. But if it is possible somehow and the option is set, there are no old
fragments to seek in. Therefore I think, seek should be forbidden if the option
is set.
Cheers,
Jörg
-----Ursprüngliche Nachricht-----
Von: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> Im Auftrag von Carl Eugen
Hoyos
Gesendet: Montag, 2. Dezember 2019 10:15
An: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Betreff: [SCISYS Possible Spam] Re: [FFmpeg-devel] [PATCH] Patch for memory
optimization with QuickTime/MP4
Am Mo., 2. Dez. 2019 um 10:05 Uhr schrieb Jörg Beckmann
<joerg.beckm...@scisys.com>:
>
> Hi,
>
> this patch invents a new option "discard_fragments" for the MP4/Quicktime/MOV
> decoder. If the option is not set, nothing changes at all. If it is set, old
> fragments are discarded as far as possible on each call to switch_root. For
> pure audio streams, the memory usage is now constant. For video streams, the
> memory usage is reduced. I've tested it with audio streams received from a
> professional DAB+ receiver and with video streams created on my own with
> "ffmpeg -i <video>.m4v -c:a:0 copy -c:v copy -c:s copy -f ismv -movflags
> frag_keyframe -movflags faststart tcp://localhost:1234?listen" and "ffmpeg -i
> tcp://localhost:1234 -c:a copy -c:v copy -c:s copy -y <output>". Does someone
> know sources for MP4 video streams? I could not find any with more than a few
> minutes. That's not sufficient to test memory usage.
>
> Cheers,
> Jörg
> ---
> libavformat/isom.h | 1 +
> libavformat/mov.c | 52 +++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/isom.h b/libavformat/isom.h index
> 4943b80ccf..9b4753f4d7 100644
> --- a/libavformat/isom.h
> +++ b/libavformat/isom.h
> @@ -268,6 +268,7 @@ typedef struct MOVContext {
> int advanced_editlist;
> int ignore_chapters;
> int seek_individually;
> + int discard_fragments;
> int64_t next_root_atom; ///< offset of the next root atom
> int export_all;
> int export_xmp;
> diff --git a/libavformat/mov.c b/libavformat/mov.c index
> 7553a7fdfc..3a5cfa23f8 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -7698,8 +7698,11 @@ static int should_retry(AVIOContext *pb, int
> error_code) { static int mov_switch_root(AVFormatContext *s, int64_t
> target, int index) {
> - int ret;
> + int ret, i;
> MOVContext *mov = s->priv_data;
> + AVStream *st = NULL;
> + MOVStreamContext *sc;
> + MOVFragment *frag;
> if (index >= 0 && index < mov->frag_index.nb_items)
> target = mov->frag_index.item[index].moof_offset;
> @@ -7721,6 +7724,46 @@ static int mov_switch_root(AVFormatContext *s, int64_t
> target, int index)
> mov->found_mdat = 0;
> + if (mov->discard_fragments) {
> + frag = &mov->fragment;
> +
> + for (i = 0; i < mov->fc->nb_streams; i++) {
> + if (mov->fc->streams[i]->id == frag->track_id) {
> + st = mov->fc->streams[i];
> + break;
> + }
> + }
> +
> + if (!st) {
> + av_log(mov->fc, AV_LOG_WARNING, "could not find
> + corresponding track id %u\n", frag->track_id);
How can this happen?
> + } else {
> + sc = st->priv_data;
> +
> + switch (st->codecpar->codec_type) {
> + case AVMEDIA_TYPE_AUDIO:
> + case AVMEDIA_TYPE_SUBTITLE:
> + /* Freeing VIDEO tables leads to corrupted video when
> writing to eg. MKV */
> + av_freep(&st->index_entries);
> + st->nb_index_entries = 0;
> + st->index_entries_allocated_size = 0;
> +
> + sc->current_index = 0;
> + sc->current_sample = 0;
> +
> + av_freep(&sc->ctts_data);
> + sc->ctts_data = NULL;
> + sc->ctts_allocated_size = 0;
> + sc->ctts_count = 0;
> + break;
> + }
> +
> + av_free(mov->frag_index.item->stream_info);
> + av_freep(&mov->frag_index.item);
> + mov->frag_index.allocated_size = 0;
> + mov->frag_index.nb_items = 0;
> + }
> + }
> +
> ret = mov_read_default(mov, s->pb, (MOVAtom){ AV_RL32("root"), INT64_MAX
> });
> if (ret < 0)
> return ret;
> @@ -7975,6 +8018,9 @@ static int mov_read_seek(AVFormatContext *s, int
> stream_index, int64_t sample_ti
> int sample;
> int i;
> + if (mc->discard_fragments) // Seeking is not possible if fragments are
> discarded.
> + return AVERROR(ENOTSUP);
I guess this is only true if the stream actually is fragmented.
> +
> if (stream_index >= s->nb_streams)
> return AVERROR_INVALIDDATA;
> @@ -8063,6 +8109,10 @@ static const AVOption mov_options[] = {
> { "decryption_key", "The media decryption key (hex)",
> OFFSET(decryption_key), AV_OPT_TYPE_BINARY, .flags =
> AV_OPT_FLAG_DECODING_PARAM },
> { "enable_drefs", "Enable external track support.",
> OFFSET(enable_drefs), AV_OPT_TYPE_BOOL,
> {.i64 = 0}, 0, 1, FLAGS },
> + {"discard_fragments",
> + "Discards fragments after they have been read to support live
> streams.",
> + OFFSET(discard_fragments), AV_OPT_TYPE_BOOL, { .i64 = 0 },
> + 0, 1, FLAGS },
Carl Eugen
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